So you want to build your own biodome?

I do and have tried scheming up a way to. A multiple layered system starting with a sunken 20' 30ft diameter 700 ft2 earth bag that’s the substructure for larger domes going from layer 1 to layer 4. I used deep research to string these ideas together for cheap, doable, and nice.

Below is a comprehensive DIY kit guide outlining a prototype build of a 20′-tall biodome with an integrated internal tower. This prototype serves as the foundation for Layer 1 (a sunken, terraced garden with a central pond/gazebo) and describes how to transition from Layer 1 to Layer 2 (the enclosing dome superstructure). The guide includes dimensions, materials estimates, parts lists, and a logical scope of work.

I. Overview & Design Concept

• Prototype Scale: A 20′-tall dome with an overall footprint of approximately 30′ in diameter.
• Layer 1 (Substructure):
• A sunken circular pit with a spiraling, terraced retaining wall constructed using earthbags.
• A central pond (approx. 6′ diameter, 2–3′ deep) with a small internal tower/gazebo built on a concrete pad.
• Integrated utility conduits (electrical, water, drainage) are run through the earthbag walls.
• Layer 2 (Superstructure):
• An enclosing geodesic dome (using modular or pre-fabricated panels) that mounts onto a bond beam along the top of Layer 1.
• Extended utility networks, venting, and solar integration are added as part of this phase.

The design is modular and sustainable — with earthbag construction for natural thermal mass, a well-drained foundation, and planned conduits for future automation.

II. Detailed Dimensions & Materials Estimates

A. Layer 1 — Sunken Terraced Garden & Foundation

1. Excavation & Foundation:

• Pit Dimensions:
• Footprint: 30′ diameter circle (area ≈ 706 ft²).
• Depth: Center excavation reaches 4–6′ deep; terraces step up gradually.
• Foundation Base:
• Gravel Layer: 6″ thick covering 706 ft² → ≈ 353 ft³ (approx. 18 tons).
• Sand: A similar volume for leveling and as a cap for utility conduits.
• Waterproofing:
• 20-mil heavy-duty polyethylene vapor barrier covering ≈800 ft² (~$800–$1,600).

2. Earthbag Wall Construction:

• Earthbag Walls (Retaining/Spiral):
• Circumference: ≈ 94′ (π × 30′).
• Wall Height: 4′ (about 8 courses, assuming 6″ per course).
• Bags Required: ≈ 94 bags per course × 8 courses = ~752 bags (round up to 800 for waste).
• Fill Material:
• First course: gravel-filled; subsequent courses: stabilized subsoil.
• Reinforcement:
• Two strands of 4-point barbed wire per course (approx. 1,600 ft total).
• Bond Beam:
• A continuous 4″×8″ reinforced concrete ring around the 94′ circumference (~21 ft³ of concrete, plus rebar), estimated at $5,000 total.

3. Central Pond & Internal Tower (Gazebo):

• Pond:
• Dimensions: 6′ diameter, 2–3′ deep.
• Liner: EPDM or heavy-duty pond liner for ≈30 ft² area (~$150).
• Central Tower/Gazebo:
• Footprint: Approximately 4′ diameter.
• Height: Initially 8′ tall; built on a small concrete pad (or reinforced earthbag island) anchored in the pond.

4. Utility Components (Layer 1):

• Electrical Conduits:
• 1″ PVC conduit — approximately 100 ft total (~$200 including fittings).
• Water Pipes:
• 1–2″ PVC pipes — approximately 50 ft total (~$100 total).
• Basic Solar & Pump Test Kit:
• 100W solar panel ($150) plus a small water pump ($100).

5. Finishing Materials:

• Plaster & Mesh:
• Wire mesh (chicken wire or stucco mesh) to cover walls, plus earthen plaster materials — estimated $200.
• Miscellaneous Tools/Supplies:
• Shovels, tampers, buckets, stakes, etc. — roughly $500.

B. Layer 2 — Dome Superstructure

1. Dome Frame & Cover:

• Dome Dimensions:
• Base: 30′ diameter; Height: 20′.
• Dome Frame Materials:
• Aluminum/steel struts: approximately 300 ft total (~$1,500).
• Connectors/hubs: ~$500.
• Dome Covering Panels:
• Polycarbonate panels covering ≈706 ft²; estimated cost: $10–$15 per ft² → approximately $8,000–$10,500.
• Fasteners & Sealants:
• Weatherproof connectors, sealants, bolts: $1,000–$2,000.

2. Utility Extensions & Integration:

• Extended Conduits & Wiring:
• Additional PVC conduit, wiring, and junction boxes: $500.
• Additional Solar Panels (for dome integration):
• Extra panels: ~$1,000.
• HVAC & Ventilation Components:
• Pop-open vent panels, extended ducting, and air tubes: $500–$1,000.

3. Bond Beam Interface Enhancements:

• Sealing & Waterproofing:
• Extra waterproof membrane and patching at the junction: $500–$1,000.

4. Interior Finishes & Access:

• Spiral Staircase/Ramp:
• Pre-fabricated steps or wooden decking for a continuous ramp from dome entry to Layer 1 — approx. $1,000.
• Additional Insulation/Lighting (Optional):
• LED grow lights and extra insulation panels: $1,000–$2,000.

III. Scope of Work: Transition from Layer 1 to Layer 2

Phase 1: Finalizing Layer 1

1. Excavation & Foundation:

• Mark and excavate a 30′-diameter pit, deepening gradually to 4–6′ in the center.
• Create a spiraled terrace layout with level steps and install a French drain in a rubble trench.
• Cover the pit floor with a 6″ gravel layer and a vapor barrier (polyethylene sheet).

1. Constructing Earthbag Retaining Walls:

• Lay ~800 earthbags in staggered courses along the spiral perimeter.
• Fill the first course with gravel, subsequent courses with stabilized soil.
• Place two strands of barbed wire between courses and embed rebar for added stability.
• Complete a continuous bond beam at the top with reinforced concrete.

1. Pond & Internal Tower (Gazebo):

• Excavate and form a 6′-diameter central pond; install an EPDM liner and edge treatment.
• Construct a central concrete pad/island in the pond; erect a basic 8′-tall gazebo structure on it.

1. Utility Installation:

• Run electrical conduit and water pipes through planned channels.
• Install basic solar and pump test units.

1. Finishing & Landscaping:

• Plaster the interior side of the earthbag walls with a lime or earthen plaster and affix mesh.
• Backfill terraces, create a spiral path with pavers or wooden steps, and plant an early garden.

Phase 2: Transitioning to Layer 2

1. Preparing the Bond Beam Interface:

• Verify and level the top of Layer 1; install or patch the bond beam with waterproof membranes.
• Embed anchor bolts in the final earthbag course.

1. Dome Frame Assembly:

• Erect the geodesic dome frame (30′ diameter, 20′ tall) on scaffolding.
• Secure the dome frame to the bond beam via pre-embedded anchors.
• Install aluminum/steel struts, connectors, and assemble the dome according to kit instructions.

1. Installing Dome Covering:

• Mount polycarbonate panels to the frame using weatherproof fasteners and sealants.
• Ensure all seams are sealed for a weather-tight enclosure.

1. Utility & HVAC Integration:

• Extend the existing electrical and water conduits into the new dome structure.
• Install additional vent panels and extend earth tubes for passive ventilation.
• Integrate extra solar panels on the dome’s exterior if desired.

1. Interior Finishing & Access:

• Install a spiral staircase or ramp connecting the dome’s entrance with the Layer 1 terrace.
• Complete interior finishes (wall treatments, additional insulation, and lighting).

1. Commissioning:

• Test all systems: monitor temperature, humidity, airflow, and water drainage.
• Adjust automated controls and verify that utilities extend properly into the new layer.
• Initiate a trial production cycle (grow a few test plants, run a water circulation test, etc.).

IV. Estimated Total DIY Budget (Prototype Scale)

• Layer 1 (Substructure) Costs: $20k–$30k
• Layer 2 (Dome Superstructure) Costs: $30k–$50k
• Additional Tools/Contingencies: $5k–$10k
• Total Estimate: Approximately $55k–$90k (subject to regional material costs and labor availability).

V. Conclusion

This DIY kit guide presents a detailed, scalable plan to build a 20′-tall prototype biodome that integrates a sunken, terraced earthbag garden (Layer 1) with a modular, enclosed geodesic dome (Layer 2). With precise dimensions, materials estimates, parts lists, and a step-by-step scope of work, the guide lays out a clear path from excavation and foundation through to full enclosure and system integration. Once successfully commissioned, this prototype will serve as a robust, climate-proof foundation for future expansion into a full-scale, self-sustaining biodome.

Would you like additional diagrams, further material specifications, or more detailed cost breakdowns on any specific component?

DIY Prototype Dome (20′ Tall) with Internal Tower – Construction Guide

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Introduction: This guide outlines how to build a ~20-foot-tall prototype dome (Layer 1 of a full biodome) with an internal tower/gazebo. The prototype is essentially a sunken ground floor that will support later layers. We’ll cover the required materials, step-by-step construction (from excavation through interior landscaping), key structural and environmental considerations (drainage, ventilation, etc.), and how to plan for future expansion. The goal is a stable, waterproof earthbag foundation that functions as a garden-filled dome base, ready to be expanded into a full-scale biodome.

1. Materials List

• Earthbags and Fill Material: A large supply of woven polypropylene bags (e.g. feed or sandbags) and soil to fill them. Use subsoil (high clay content) or a stabilized earth mix (soil with a bit of cement or lime) for the bags​
• instructables.com
• ​
• commons.wikimedia.org
• . Also gather gravel and coarse sand – gravel is used to fill the lower courses of bags and for drainage layers​
• instructables.com
• ​
• en.wikipedia.org
• . Sand is useful for leveling and as part of earthen plasters later. Tip: Double-bag the first few courses with gravel to create a robust, moisture-resistant foundation​
• instructables.com
• .
• Aircrete (Optional): If available, lightweight aircrete (foamed concrete) can be used for added insulation or structural elements. Aircrete blocks or panels might line parts of the interior or form a thin inner wall. In one underground earthbag build, 2″ thick aircrete walls were poured against the earthbags for insulation and moisture protection​
• reddit.com
• – this is optional but can help keep the space dry and temperate.
• Structural Reinforcements: Barbed wire – critical for earthbag construction – to lay between courses of bags for tensile strength and to prevent slipping​
• instructables.com
• ​
• en.wikipedia.org
• . You’ll need two strands of 4-point barbed wire per layer of bags. Also acquire some steel rebar rods (e.g. 3–4 foot lengths of #4 rebar): these can be hammered through courses or used as anchors for the tower and future layers. Mesh (such as chicken wire or stucco mesh) is useful to wrap curved walls and the outside of bags before plastering, adding stability and helping plaster adhere. If your design includes a gazebo or small tower structure inside, have lumber or metal hardware for that (e.g. pressure-treated posts, brackets, and fasteners).
• Utility Conduits: Durable pipes and conduit for running utilities through or under the structure. Plan for electrical conduit (PVC or metal) to carry wiring – it’s wise to embed these during construction to avoid retrofitting later​
• earthbagbuilding.wordpress.com
• . Include some 1″ or 2″ PVC pipes for water lines (to feed the pond or future plumbing fixtures) and drainage pipes. A perforated drain pipe (French drain) will be needed for groundwater drainage around the dome’s base. Also gather any vent piping for air – for instance, 4–6″ pipes if you plan to install passive air tubes for ventilation. Having these conduits on hand allows you to integrate utilities into the walls and floor as you build, rather than digging later.
• Waterproofing & Vapor Barriers: Materials to keep moisture out of your earthbag structure. Thick plastic sheeting (e.g. 20-mil polyethylene) or EPDM rubber liner will serve as a waterproof barrier around the exterior of the bags and under the floor. (In one earthbag “hobbit house” build, 20-mil plastic wrap was used to encase the bag walls as a moisture barrier​
• reddit.com
• .) For the pond, you’ll need a dedicated pond liner (EPDM or heavy pond plastic). Include geotextile fabric or landscaping fabric to separate soil from gravel in drainage systems. Additionally, gather tarps or roofing felt to protect areas during construction and some insulating foam board (optional) if you plan to insulate behind retaining walls or under the floor.
• Miscellaneous: Other handy items include: buckets, shovels, tampers, water source (for moistening fill or mixing aircrete), twine or stringlines and stakes (for layout and level guides), a sturdy ladder (for climbing in/out of the pit), and basic tools (utility knife, wire cutters, sewing needle or fencing needle for stitching bags, etc.)​
• instructables.com
• ​
• instructables.com
• . Also stockpile plaster ingredients (clay, sand, fiber, or cement and lime) to finish surfaces later, and landscaping supplies (good topsoil, compost, seeds/plants) for the interior garden.

2. Step-by-Step Construction

Step 1: Excavation and Foundation

1. Mark the Layout: Begin by marking out the dome’s footprint on the ground. Plan a diameter sufficient for a ~20′ height dome (e.g. roughly 30′ diameter circular area for a hemisphere dome of ~20′ height). Include the outline of any spiral ramp or steps you want descending into the pit. Mark the center (where the pond and internal tower will go) and radiate out a spiral path if design calls for it.
2. Excavate a Spiraled Pit: Dig the pit to form the sunken Layer-1 interior. The design calls for a spiral descent – imagine a gentle ramp or terraced steps wrapping around the interior, going down to the central pond area. Start digging at the perimeter where an entrance could be, and slope downward as you go around. The excavation should resemble a bowl or amphitheater: deeper in the center (where the pond will be) and higher along the edges. Plan for the deepest point (pond center) to be several feet below grade (exact depth can be 4–6 feet, or deeper if you want more headroom). Carve out rough terraces along the spiral where the retaining walls will sit – each terrace step might be 2–3 feet of vertical drop. Ensure the pit’s sides are not vertical banks of loose soil; cut them at a stable angle or support them soon with bags to prevent collapse.
3. Prepare the Subsoil Base: At the bottom of your pit (and on each terrace level), compact the native soil. Remove any organic topsoil and reach stable subsoil​
4. instructables.com
5. . If the soil is clayey and impermeable, consider adding a “sump” or lowest point drain. Now install a rubble trench foundation at the base of all walls: dig a narrow trench (about 12″ wide and 12″ deep) following the path of the planned earthbag walls (e.g. a spiral ring in plan view) down to undisturbed ground​
6. en.wikipedia.org
7. . Fill this trench with crushed stone or gravel. This rubble trench will act as a French drain to carry away moisture and also as a stable footing for the first course of bags. Make sure the trench has a slight slope toward a desired drainage exit or “weep point” – ideally daylighting somewhere lower than your floor, or to a dry well. Lay drainage pipe: At the lowest point of the trench, lay a perforated drain pipe that leads out of the pit (or to a dry well). Encase it in gravel. This will ensure water doesn’t accumulate under your floor (a French drain system is “a must” for underground structures​
8. reddit.com
9. ).
10. Gravel and Sand Lining: Cover the entire pit floor with a layer of coarse gravel (~4″ thick) and tamp it down. This creates a capillary break for moisture and a level base. Over the gravel, you can add a layer of sand to help with leveling the first bags and to protect any plastic liner if you choose to lay one. At this stage, if you plan a floor vapor barrier, lay heavy plastic sheeting across the pit floor (perhaps even running it up the sides of the pit a couple feet). This plastic can go under the first bag courses to further stop ground moisture. Many builders omit a full floor liner if drainage is good, but in wetter climates it’s wise to include one.
11. Start the First Earthbag Course: Fill the first row of bags with gravel (this is sometimes called the gravel bag foundation). Using gravel in the bottom course instead of soil prevents wicking of moisture into the walls​
12. instructables.com
13. . Double-bag these or use two layers of bags for extra strength​
14. instructables.com
15. . Place the bags end to end along your trench outline (e.g. following the spiral curve). Tamp them flat and level as you go. The gravel bags will form the base of the terraced retaining walls. If your spiral has multiple levels, start at the lowest level and work outwards/upwards; you may end up with a few “steps” of bag foundations at different heights corresponding to terrace levels. After completing one continuous course (or each section of a terraced level), lay two strands of barbed wire on top of the bags (about 4–6 inches in from the bag edges)​
16. instructables.com
17. . Pin the wire in place with small rocks or U-shaped staples pressed into the bags​
18. instructables.com
19. .
20. Build Up Foundation Courses: Continue laying courses of earthbags for the retaining walls. After the initial gravel bag layer(s), you can switch to soil-filled earthbags for subsequent courses (the gravel foundation under them will keep moisture at bay)​
21. instructables.com
22. ​
23. instructables.com
24. . Each new course should be offset (staggered) from the one below, like laying bricks in a running bond​
25. en.wikipedia.org
26. . Because you are creating terraced walls, the upper courses will be set back slightly from the edge of the one below, matching the slope of the excavation. Keep following the spiral layout – you’re essentially building a spiral earthbag retaining wall that will hold back the earth of each terrace. Embed vertical rebar at intervals for extra strength: for example, every 3–4 feet along the wall, hammer a rebar rod down through the bags (this pins multiple courses together). Where the wall curves sharply or at corners of terraces, rebar and careful tamping help maintain strength. By the end of this step, you should have the pit lined with sturdy earthbag walls, stepping down in a spiral to the center.

Step 2: Structural Build – Terraced Earthbag Walls

Stacking earthbags in courses creates a stable, load-bearing wall for the dome’s base. In this prototype, the bags form spiraling terraced retaining walls that define the sunken interior. Each bag is filled (~90% full) with either gravel or subsoil, then tightly sealed (folded or sewn shut) and tamped in place. Barbed wire between every course locks the bags together, preventing slippage and adding tensile strength​

instructables.com

​

en.wikipedia.org

. As the image shows, polypropylene bags filled with earth are very adaptable – they can be curved and stepped to follow our spiral design.

1. Raise the Earthbag Walls: Continue laying earthbag courses to reach the desired height for each terrace. Typically, an earthbag wall can be built straight up or in an inward curve (for domes). Here, our retaining walls are partly against earth, so we build against the excavated slope – this gives natural back support. Aim for each terrace wall to be roughly 2–3 feet high (or whatever your step height is) so that you have multiple “steps” climbing out of the pit. Ensure that the top of each earthbag wall is level and well-tamped. You might embed wooden deadmen or anchors in some courses if later you want to attach flooring, railings, or the gazebo posts – for example, placing short pieces of 2×4 or pipe in a joint between bag courses where a future anchor is needed​
2. earthbagbuilding.wordpress.com
3. ​
4. earthbagbuilding.wordpress.com
5. . Always add the two lines of barbed wire on each course before the next one is laid, and pull bags tight to each other to eliminate gaps.
6. Shape the Spiral Ramp: As you build the walls, shape the earthen ramp or steps that spiral up alongside them. You can use earthbag steps too – for instance, if the spiral has a gentle slope, the tamped earthbag courses themselves create a walkable path. If the slope is steeper, you might build stairs by turning bags perpendicular to make steps, or use wooden treads anchored into the bags. At this stage, decide where the entrance to Layer 1 will be (if this layer will be accessible now). Leave a gap in the bag wall for a doorway if needed, or plan to use the spiral ramp itself as the entry path from ground level.
7. Integrate the Internal Tower Base: The internal tower or gazebo will likely sit at the center (perhaps spanning the pond or adjacent to it). Prepare a foundation for this tower. One approach is to use earthbags to create a small central pillar or island. For example, you could lay a ring of bags (or even bricks or stones) in the middle of the pond area as a footing for the gazebo posts. Alternatively, pour a small concrete pad or set concrete pier blocks in the center before you construct the pond. Ensure this mini-foundation is level and stable – it should reach high enough (or be built up later) so that when the pond is excavated around it, it stands as a central island. Reinforce this spot with extra gravel beneath and perhaps a circle of rebar driven in for stability. (If the internal tower will eventually support upper structures, you might even cast a concrete core or set a metal pipe that can later be extended upward.)
8. Bond Beam or Top Plate (Optional): Once the earthbag walls reach the desired height (likely near ground level at the outer perimeter of Layer 1), consider installing a bond beam on top. This could be a reinforced concrete beam or a timber ring that caps the earthbag wall. Its purpose is to tie the wall together and provide a solid base for the next layer or any roof you might temporarily add​
9. en.wikipedia.org
10. . For a circular dome, a common technique is to embed a circle of rebar or a wire rope in the final course of bags as a tension ring. In our case, since this is a foundation for future expansion, you might set anchor bolts or rebar stubs in the top course that can later attach to the structure above. (For example, if the next layer is an above-ground dome, those anchors will secure it to these walls.)
11. Plastering the Earthbag Walls: At the prototype stage, you should stabilize the exposed earthbags so they aren’t damaged by UV or rain. Apply an earthen plaster or cement stucco to any exposed part of the bags on the interior. Before plaster, attach your wire mesh over the bags for reinforcement. If this layer will remain exposed to weather for some time, add a waterproof plaster or lime plaster on the outside. However, since much of the bag wall is against earth (the terrace backfill), focus on plastering the interior faces for now. You may also place a waterproof membrane on the exterior side of the outermost bag wall (for example, wrapping the outside of the wall with 6-mil plastic before backfilling soil against it, to keep moisture out of the wall).
12. Backfill and Berm: After the walls are up and plastered on the inside, you can backfill soil behind them (on the terraces). Refill the excavated areas between the spiral walls with the soil you dug out, tamping gently to reduce settlement (don’t overly compact directly against the bag walls). This recreates the terraced ground on the outside of each wall. Slope this backfill soil so that any water will drain away from the bag wall. The top terrace (outer ground level) should be graded to direct rainwater away from the dome pit. Later you can landscape these berms with plants (perhaps succulents or grasses) to prevent erosion. For now, you might lay tarp or plastic over raw soil if heavy rains are expected, until vegetation is planted.

Step 3: Pond & Gazebo Setup

1. Dig the Pond Basin: At the center of the pit, excavate the pond if you haven’t already. Shape it as desired – possibly round or kidney-shaped, occupying the lowest part of Layer 1. Make it deep enough for aquatic plants or fish (common depths are 2–3 feet, with some shallow shelves on the edges for plants). Slope the sides gently if possible. Ensure the bottom of the pond is still above the level of your French drain so that any leakage will get carried away. Remove any sharp rocks from the basin.
2. Line with Sand or Underlayment: Cover the pond excavation with a layer of soft sand or an old carpet/underlayment to protect the liner. This prevents punctures. If your pond design includes the central island for the gazebo, shape the sand around that area accordingly (you can keep the island unlined if it’s made of concrete or bags, but ensure water can’t undermine it – you might encircle it with liner separately).
3. Install the Pond Liner: Lay out the EPDM or heavy-duty pond liner into the pond hole. Smooth it out, making sure it overlaps well beyond the edges. At the perimeter of the pond, secure the liner by weighing it with rocks or temporarily pinning it. If the pond touches any earthbag edges (for instance, if the inner retaining wall forms part of the pond edge), run the liner slightly up that wall to ensure a waterproof seal. Superadobe (earthbag) techniques have even been used to shape ponds and pools by lining them with waterproof membranes​
4. earthbagstore.com
5. – here the liner is what truly holds the water.
6. Edge Treatment: To make a natural-looking pond edge, you can place stones around the rim on top of the liner, or fold the liner under soil berms. Since this pond will eventually be inside the dome, you might create a low retaining edge with earth or bags to keep soil out. For now, consider adding a small ledge of sandbags around the pond lip to hold the liner in place (these could later be hidden by rocks or plants).
7. Gazebo / Tower Construction: With the pond in place, you can build the internal gazebo (the “tower”). If you prepared an island or footing, set your posts on that. For example, if using wood posts, you might have cast metal post anchors in a small concrete island at the pond center – now attach your vertical posts. A simple gazebo could be a four-post structure with cross-beams, perhaps 8–10 feet tall (tall enough to be an “internal tower” and eventually reach toward the next layer). Use rot-resistant wood or treat it against moisture, since it will be in a humid environment. If the gazebo is in the pond’s center, you might connect it to the edge with a little footbridge or stepping stones. Ensure everything is structurally sound – anchor the gazebo well so it can handle people or loads (consider braces between posts). This gazebo not only provides a shaded sitting area or vertical element now, but it can act as a support structure for the future (for example, it could later help hold up a upper-floor or be a frame to hang lights and planters).
8. Finishing Touches for Pond: Add gravel or rocks to the bottom of the pond liner to weigh it down and provide a natural substrate. Fill the pond with water (even if you don’t keep it full all the time now, a test fill checks for leaks). If desired, introduce some water plants (like water lilies or reeds) – they’ll start conditioning the water and controlling algae. Down the line, this pond will serve as thermal mass and possibly part of an aquaponics system, but even now it contributes humidity and a pleasing environment. Tip: Paint the interior of the pond liner a dark color or weigh down floating covers if it will be stagnant; dark water absorbs heat and also prevents algal blooms​
9. growingspaces.com
10. ​
11. growingspaces.com
12. .
13. Gazebo Decking and Features: If your gazebo is meant to be a relaxing spot, install a floor or platform. You can lay wooden decking on the posts, or create a little bridge across a section of the pond leading to a platform. Since this is a prototype, you might keep it simple – a small raised platform overlooking the pond, accessible via a stepping-stone path. This internal tower/gazebo will later be a highlight of the dome, so even at this stage, make it functional (a place to sit, meditate, or hang plants).

Step 4: Conduit & Utility Integration

DIY Prototype Dome (20′ Tall) with Internal Tower — Construction Guide

Introduction: This guide outlines how to build a ~20-foot-tall prototype dome (Layer 1 of a full biodome) with an internal tower/gazebo. The prototype is essentially a sunken ground floor that will support later layers. We’ll cover the required materials, step-by-step construction (from excavation through interior landscaping), key structural and environmental considerations (drainage, ventilation, etc.), and how to plan for future expansion. The goal is a stable, waterproof earthbag foundation that functions as a garden-filled dome base, ready to be expanded into a full-scale biodome.

1. Materials List

• Earthbags and Fill Material: A large supply of woven polypropylene bags (e.g. feed or sandbags) and soil to fill them. Use subsoil (high clay content) or a stabilized earth mix (soil with a bit of cement or lime) for the bags​
• instructables.com
• ​
• commons.wikimedia.org
• . Also gather gravel and coarse sand — gravel is used to fill the lower courses of bags and for drainage layers​
• instructables.com
• ​
• en.wikipedia.org
• . Sand is useful for leveling and as part of earthen plasters later. Tip: Double-bag the first few courses with gravel to create a robust, moisture-resistant foundation​
• instructables.com
• .
• Aircrete (Optional): If available, lightweight aircrete (foamed concrete) can be used for added insulation or structural elements. Aircrete blocks or panels might line parts of the interior or form a thin inner wall. In one underground earthbag build, 2″ thick aircrete walls were poured against the earthbags for insulation and moisture protection​
• reddit.com
• – this is optional but can help keep the space dry and temperate.
• Structural Reinforcements: Barbed wire — critical for earthbag construction — to lay between courses of bags for tensile strength and to prevent slipping​
• instructables.com
• ​
• en.wikipedia.org
• . You’ll need two strands of 4-point barbed wire per layer of bags. Also acquire some steel rebar rods (e.g. 3–4 foot lengths of #4 rebar): these can be hammered through courses or used as anchors for the tower and future layers. Mesh (such as chicken wire or stucco mesh) is useful to wrap curved walls and the outside of bags before plastering, adding stability and helping plaster adhere. If your design includes a gazebo or small tower structure inside, have lumber or metal hardware for that (e.g. pressure-treated posts, brackets, and fasteners).
• Utility Conduits: Durable pipes and conduit for running utilities through or under the structure. Plan for electrical conduit (PVC or metal) to carry wiring — it’s wise to embed these during construction to avoid retrofitting later​
• earthbagbuilding.wordpress.com
• . Include some 1″ or 2″ PVC pipes for water lines (to feed the pond or future plumbing fixtures) and drainage pipes. A perforated drain pipe (French drain) will be needed for groundwater drainage around the dome’s base. Also gather any vent piping for air — for instance, 4–6″ pipes if you plan to install passive air tubes for ventilation. Having these conduits on hand allows you to integrate utilities into the walls and floor as you build, rather than digging later.
• Waterproofing & Vapor Barriers: Materials to keep moisture out of your earthbag structure. Thick plastic sheeting (e.g. 20-mil polyethylene) or EPDM rubber liner will serve as a waterproof barrier around the exterior of the bags and under the floor. (In one earthbag “hobbit house” build, 20-mil plastic wrap was used to encase the bag walls as a moisture barrier​
• reddit.com
• .) For the pond, you’ll need a dedicated pond liner (EPDM or heavy pond plastic). Include geotextile fabric or landscaping fabric to separate soil from gravel in drainage systems. Additionally, gather tarps or roofing felt to protect areas during construction and some insulating foam board (optional) if you plan to insulate behind retaining walls or under the floor.
• Miscellaneous: Other handy items include: buckets, shovels, tampers, water source (for moistening fill or mixing aircrete), twine or stringlines and stakes (for layout and level guides), a sturdy ladder (for climbing in/out of the pit), and basic tools (utility knife, wire cutters, sewing needle or fencing needle for stitching bags, etc.)​
• instructables.com
• ​
• instructables.com
• . Also stockpile plaster ingredients (clay, sand, fiber, or cement and lime) to finish surfaces later, and landscaping supplies (good topsoil, compost, seeds/plants) for the interior garden.

2. Step-by-Step Construction

Step 1: Excavation and Foundation

1. Mark the Layout: Begin by marking out the dome’s footprint on the ground. Plan a diameter sufficient for a ~20′ height dome (e.g. roughly 30′ diameter circular area for a hemisphere dome of ~20′ height). Include the outline of any spiral ramp or steps you want descending into the pit. Mark the center (where the pond and internal tower will go) and radiate out a spiral path if design calls for it.
2. Excavate a Spiraled Pit: Dig the pit to form the sunken Layer-1 interior. The design calls for a spiral descent — imagine a gentle ramp or terraced steps wrapping around the interior, going down to the central pond area. Start digging at the perimeter where an entrance could be, and slope downward as you go around. The excavation should resemble a bowl or amphitheater: deeper in the center (where the pond will be) and higher along the edges. Plan for the deepest point (pond center) to be several feet below grade (exact depth can be 4–6 feet, or deeper if you want more headroom). Carve out rough terraces along the spiral where the retaining walls will sit — each terrace step might be 2–3 feet of vertical drop. Ensure the pit’s sides are not vertical banks of loose soil; cut them at a stable angle or support them soon with bags to prevent collapse.
3. Prepare the Subsoil Base: At the bottom of your pit (and on each terrace level), compact the native soil. Remove any organic topsoil and reach stable subsoil​
4. instructables.com
5. . If the soil is clayey and impermeable, consider adding a “sump” or lowest point drain. Now install a rubble trench foundation at the base of all walls: dig a narrow trench (about 12″ wide and 12″ deep) following the path of the planned earthbag walls (e.g. a spiral ring in plan view) down to undisturbed ground​
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7. . Fill this trench with crushed stone or gravel. This rubble trench will act as a French drain to carry away moisture and also as a stable footing for the first course of bags. Make sure the trench has a slight slope toward a desired drainage exit or “weep point” — ideally daylighting somewhere lower than your floor, or to a dry well. Lay drainage pipe: At the lowest point of the trench, lay a perforated drain pipe that leads out of the pit (or to a dry well). Encase it in gravel. This will ensure water doesn’t accumulate under your floor (a French drain system is “a must” for underground structures​
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9. ).
10. Gravel and Sand Lining: Cover the entire pit floor with a layer of coarse gravel (~4″ thick) and tamp it down. This creates a capillary break for moisture and a level base. Over the gravel, you can add a layer of sand to help with leveling the first bags and to protect any plastic liner if you choose to lay one. At this stage, if you plan a floor vapor barrier, lay heavy plastic sheeting across the pit floor (perhaps even running it up the sides of the pit a couple feet). This plastic can go under the first bag courses to further stop ground moisture. Many builders omit a full floor liner if drainage is good, but in wetter climates it’s wise to include one.
11. Start the First Earthbag Course: Fill the first row of bags with gravel (this is sometimes called the gravel bag foundation). Using gravel in the bottom course instead of soil prevents wicking of moisture into the walls​
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13. . Double-bag these or use two layers of bags for extra strength​
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15. . Place the bags end to end along your trench outline (e.g. following the spiral curve). Tamp them flat and level as you go. The gravel bags will form the base of the terraced retaining walls. If your spiral has multiple levels, start at the lowest level and work outwards/upwards; you may end up with a few “steps” of bag foundations at different heights corresponding to terrace levels. After completing one continuous course (or each section of a terraced level), lay two strands of barbed wire on top of the bags (about 4–6 inches in from the bag edges)​
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17. . Pin the wire in place with small rocks or U-shaped staples pressed into the bags​
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19. .
20. Build Up Foundation Courses: Continue laying courses of earthbags for the retaining walls. After the initial gravel bag layer(s), you can switch to soil-filled earthbags for subsequent courses (the gravel foundation under them will keep moisture at bay)​
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24. . Each new course should be offset (staggered) from the one below, like laying bricks in a running bond​
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26. . Because you are creating terraced walls, the upper courses will be set back slightly from the edge of the one below, matching the slope of the excavation. Keep following the spiral layout — you’re essentially building a spiral earthbag retaining wall that will hold back the earth of each terrace. Embed vertical rebar at intervals for extra strength: for example, every 3–4 feet along the wall, hammer a rebar rod down through the bags (this pins multiple courses together). Where the wall curves sharply or at corners of terraces, rebar and careful tamping help maintain strength. By the end of this step, you should have the pit lined with sturdy earthbag walls, stepping down in a spiral to the center.

Step 2: Structural Build — Terraced Earthbag Walls

Stacking earthbags in courses creates a stable, load-bearing wall for the dome’s base. In this prototype, the bags form spiraling terraced retaining walls that define the sunken interior. Each bag is filled (~90% full) with either gravel or subsoil, then tightly sealed (folded or sewn shut) and tamped in place. Barbed wire between every course locks the bags together, preventing slippage and adding tensile strength​

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en.wikipedia.org

. As the image shows, polypropylene bags filled with earth are very adaptable — they can be curved and stepped to follow our spiral design.

1. Raise the Earthbag Walls: Continue laying earthbag courses to reach the desired height for each terrace. Typically, an earthbag wall can be built straight up or in an inward curve (for domes). Here, our retaining walls are partly against earth, so we build against the excavated slope — this gives natural back support. Aim for each terrace wall to be roughly 2–3 feet high (or whatever your step height is) so that you have multiple “steps” climbing out of the pit. Ensure that the top of each earthbag wall is level and well-tamped. You might embed wooden deadmen or anchors in some courses if later you want to attach flooring, railings, or the gazebo posts — for example, placing short pieces of 2×4 or pipe in a joint between bag courses where a future anchor is needed​
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5. . Always add the two lines of barbed wire on each course before the next one is laid, and pull bags tight to each other to eliminate gaps.
6. Shape the Spiral Ramp: As you build the walls, shape the earthen ramp or steps that spiral up alongside them. You can use earthbag steps too — for instance, if the spiral has a gentle slope, the tamped earthbag courses themselves create a walkable path. If the slope is steeper, you might build stairs by turning bags perpendicular to make steps, or use wooden treads anchored into the bags. At this stage, decide where the entrance to Layer 1 will be (if this layer will be accessible now). Leave a gap in the bag wall for a doorway if needed, or plan to use the spiral ramp itself as the entry path from ground level.
7. Integrate the Internal Tower Base: The internal tower or gazebo will likely sit at the center (perhaps spanning the pond or adjacent to it). Prepare a foundation for this tower. One approach is to use earthbags to create a small central pillar or island. For example, you could lay a ring of bags (or even bricks or stones) in the middle of the pond area as a footing for the gazebo posts. Alternatively, pour a small concrete pad or set concrete pier blocks in the center before you construct the pond. Ensure this mini-foundation is level and stable — it should reach high enough (or be built up later) so that when the pond is excavated around it, it stands as a central island. Reinforce this spot with extra gravel beneath and perhaps a circle of rebar driven in for stability. (If the internal tower will eventually support upper structures, you might even cast a concrete core or set a metal pipe that can later be extended upward.)
8. Bond Beam or Top Plate (Optional): Once the earthbag walls reach the desired height (likely near ground level at the outer perimeter of Layer 1), consider installing a bond beam on top. This could be a reinforced concrete beam or a timber ring that caps the earthbag wall. Its purpose is to tie the wall together and provide a solid base for the next layer or any roof you might temporarily add​
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10. . For a circular dome, a common technique is to embed a circle of rebar or a wire rope in the final course of bags as a tension ring. In our case, since this is a foundation for future expansion, you might set anchor bolts or rebar stubs in the top course that can later attach to the structure above. (For example, if the next layer is an above-ground dome, those anchors will secure it to these walls.)
11. Plastering the Earthbag Walls: At the prototype stage, you should stabilize the exposed earthbags so they aren’t damaged by UV or rain. Apply an earthen plaster or cement stucco to any exposed part of the bags on the interior. Before plaster, attach your wire mesh over the bags for reinforcement. If this layer will remain exposed to weather for some time, add a waterproof plaster or lime plaster on the outside. However, since much of the bag wall is against earth (the terrace backfill), focus on plastering the interior faces for now. You may also place a waterproof membrane on the exterior side of the outermost bag wall (for example, wrapping the outside of the wall with 6-mil plastic before backfilling soil against it, to keep moisture out of the wall).
12. Backfill and Berm: After the walls are up and plastered on the inside, you can backfill soil behind them (on the terraces). Refill the excavated areas between the spiral walls with the soil you dug out, tamping gently to reduce settlement (don’t overly compact directly against the bag walls). This recreates the terraced ground on the outside of each wall. Slope this backfill soil so that any water will drain away from the bag wall. The top terrace (outer ground level) should be graded to direct rainwater away from the dome pit. Later you can landscape these berms with plants (perhaps succulents or grasses) to prevent erosion. For now, you might lay tarp or plastic over raw soil if heavy rains are expected, until vegetation is planted.

Step 3: Pond & Gazebo Setup

1. Dig the Pond Basin: At the center of the pit, excavate the pond if you haven’t already. Shape it as desired — possibly round or kidney-shaped, occupying the lowest part of Layer 1. Make it deep enough for aquatic plants or fish (common depths are 2–3 feet, with some shallow shelves on the edges for plants). Slope the sides gently if possible. Ensure the bottom of the pond is still above the level of your French drain so that any leakage will get carried away. Remove any sharp rocks from the basin.
2. Line with Sand or Underlayment: Cover the pond excavation with a layer of soft sand or an old carpet/underlayment to protect the liner. This prevents punctures. If your pond design includes the central island for the gazebo, shape the sand around that area accordingly (you can keep the island unlined if it’s made of concrete or bags, but ensure water can’t undermine it — you might encircle it with liner separately).
3. Install the Pond Liner: Lay out the EPDM or heavy-duty pond liner into the pond hole. Smooth it out, making sure it overlaps well beyond the edges. At the perimeter of the pond, secure the liner by weighing it with rocks or temporarily pinning it. If the pond touches any earthbag edges (for instance, if the inner retaining wall forms part of the pond edge), run the liner slightly up that wall to ensure a waterproof seal. Superadobe (earthbag) techniques have even been used to shape ponds and pools by lining them with waterproof membranes​
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5. – here the liner is what truly holds the water.
6. Edge Treatment: To make a natural-looking pond edge, you can place stones around the rim on top of the liner, or fold the liner under soil berms. Since this pond will eventually be inside the dome, you might create a low retaining edge with earth or bags to keep soil out. For now, consider adding a small ledge of sandbags around the pond lip to hold the liner in place (these could later be hidden by rocks or plants).
7. Gazebo / Tower Construction: With the pond in place, you can build the internal gazebo (the “tower”). If you prepared an island or footing, set your posts on that. For example, if using wood posts, you might have cast metal post anchors in a small concrete island at the pond center — now attach your vertical posts. A simple gazebo could be a four-post structure with cross-beams, perhaps 8–10 feet tall (tall enough to be an “internal tower” and eventually reach toward the next layer). Use rot-resistant wood or treat it against moisture, since it will be in a humid environment. If the gazebo is in the pond’s center, you might connect it to the edge with a little footbridge or stepping stones. Ensure everything is structurally sound — anchor the gazebo well so it can handle people or loads (consider braces between posts). This gazebo not only provides a shaded sitting area or vertical element now, but it can act as a support structure for the future (for example, it could later help hold up a upper-floor or be a frame to hang lights and planters).
8. Finishing Touches for Pond: Add gravel or rocks to the bottom of the pond liner to weigh it down and provide a natural substrate. Fill the pond with water (even if you don’t keep it full all the time now, a test fill checks for leaks). If desired, introduce some water plants (like water lilies or reeds) — they’ll start conditioning the water and controlling algae. Down the line, this pond will serve as thermal mass and possibly part of an aquaponics system, but even now it contributes humidity and a pleasing environment. Tip: Paint the interior of the pond liner a dark color or weigh down floating covers if it will be stagnant; dark water absorbs heat and also prevents algal blooms​
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12. .
13. Gazebo Decking and Features: If your gazebo is meant to be a relaxing spot, install a floor or platform. You can lay wooden decking on the posts, or create a little bridge across a section of the pond leading to a platform. Since this is a prototype, you might keep it simple — a small raised platform overlooking the pond, accessible via a stepping-stone path. This internal tower/gazebo will later be a highlight of the dome, so even at this stage, make it functional (a place to sit, meditate, or hang plants).

Step 4: Conduit & Utility Integration

1. Electrical Wiring: Before you finalize the walls and backfill everything, run electrical conduit to any spots that will need power. For example, run a conduit from outside the dome (where you can later connect to the grid or solar panels) into the pit, terminating near the gazebo (for lights or a water pump) and perhaps around the perimeter (for future lighting or outlets). It’s much easier to embed this now: you can snake PVC conduit through the earthbag wall (between courses) — builders have successfully run conduit through earthbags​
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3. . Plan for a junction box near the gazebo or high on the wall where it will stay dry. If code requires, use outdoor-rated conduit; otherwise, some have used direct-burial cable in the earthbag courses​
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5. , but conduit is safer and allows future wiring changes. Also consider running a conduit up the internal tower if you want a light or fan at a higher point later.
6. Water Supply and Irrigation: Lay any plumbing now as well. For instance, a water inlet pipe can be run into the pond for easy filling or to feed an aquaponic system. If you plan a small waterfall or pump, include a path for that pipe and the pump’s electrical line. Likewise, stub in a water supply line that could later connect to a rainwater cistern or well — even if you don’t hook it up yet, having a pipe in place (capped for now) will make future installation easier. Run hoses or PVC under the floor or behind walls toward any place you anticipate needing water (like a future greenhouse irrigation line for the garden beds).
7. Drainage and Sump: Ensure there is a drain outlet for water in the dome. You might install a floor drain in the lowest point of the pond area (or an overflow from the pond) that ties into the French drain. For example, placing a vertical standpipe at the pond’s edge that goes down and connects to the gravel drain trench will let you empty the pond if needed or just handle overflow when it rains. Also, if you anticipate heavy rain flooding, you could incorporate a sump pit — a small gravel-filled hole with a perforated barrel in it and a sump pump — but in a well-designed rubble trench, passive drainage should suffice​
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11. .
12. Ventilation Ducts: Since this prototype will eventually be enclosed, plan for airflow now. One advanced feature is to bury a couple of earth tubes (lengths of 4–6 inch PVC pipe) that run from outside, through the ground, and open into the interior space. These earth tubes can provide natural cooling by drawing in cooler earth-tempered air​
13. earthship.com
14. . If you want to do this, trench out from the pit to somewhere 30–50 feet away and a few feet deep, lay the pipes with a slight slope (so condensation can drain), then run them into the Layer 1 space (perhaps emerging near the floor at one end of the spiral). Later, when the dome is up, you can ventilate by opening these tubes at one end and having a vent or chimney at the top of the dome (stack effect). For now, cap or screen them to prevent critters entry. Also consider leaving space for future fans or HVAC — e.g., you might cast a small hole in a wall that can hold a solar fan or just serve as an air inlet/outlet.
15. Lighting: If the prototype will be used immediately as a greenhouse/garden, think about temporary lighting. You can integrate low-voltage LED lights along the path or solar lights, using the conduits you placed. Even a simple solar fountain pump in the pond can keep water moving and add a nice touch. Running a string of lights on the gazebo is possible if you’ve run the wiring. Make sure any electrical connections in this phase are weatherproof, as the dome isn’t enclosed yet (use outdoor-rated junction boxes and GFCI outlets for safety).
16. Testing Utilities: Before finishing, test the utility lines. Pull some wires through the conduit to ensure there are no blockages (or at least a pull-cord left in the conduit). Check that water flows through any piping (no crushed segments). Verify the drainage by spraying water and seeing that it exits where intended. It’s much easier to fix any issues now, before everything is buried and landscaped.

Step 5: Interior Landscaping

1. Soil Preparation: With structural work done, focus on the interior ground of Layer 1. The terraces formed by the earthbag retaining walls create planting areas. Improve the soil on those terraces: add a layer of rich topsoil or compost on each level to create planting beds. Since the base is essentially a sunken garden, you might treat each terrace like a raised garden bed contained by earthbags. Ensure the soil is graded properly — slight slopes toward the pond for any excess water to collect there, but generally flat where plants will grow.
2. Planting: Start an early-stage garden to test the environment. Choose hardy plants that enjoy a semi-sheltered, moist environment. For example, on the lower terraces near the pond, plant water-loving species (like taro, watercress in a shallow water fringe, or wetland flowers). On higher terraces, you can plant herbs, vegetables, or small shrubs. This living layer will help stabilize the soil and also give you a head start on the biodome’s eventual ecosystem. If the dome won’t be covered for a while, select plants that can handle local weather or plan to cover them during harsh conditions. You could also incorporate a temporary greenhouse cover over the pit (e.g. a hoop house or tarp cover) to create a warm, humid microclimate for your garden — essentially using the pit as a partially subterranean greenhouse (similar to a walipini concept).
3. Pathways: Refine the spiral path for comfortable use. You can lay flat stones or pavers into the ramp to make a stable walking surface. Alternatively, use wooden steps or brick where needed. Because the earthbags form a firm edge, you can tamp earth between them for the path, or infill with gravel and then top with stepping stones. The goal is to have a clear route to walk from the entrance down to the center. Consider a small bridge or stepping stones across the pond if the spiral path doesn’t go fully around the water. Maybe a simple wooden plank bridge from the bottom of the ramp to the central gazebo. All of this makes the prototype functional as a meditative garden space.
4. Irrigation & Watering: With plants in place, set up a basic irrigation method. You might direct some pond water to plants (since pond water, enriched by fish or plant nutrients, can fertilize them). Using a bucket or a simple siphon hose can do for now. If you installed a pump in the pond, you could attach a garden hose to it. Otherwise, keep a rain barrel or water storage nearby and hand-water the terraces. The high humidity from the pond will also benefit the plants​
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6. , and as the pond “breathes” it adds moisture to the air which can condense on cool surfaces, passively watering some parts.
7. Finishing and Aesthetics: Finally, add aesthetic touches: place some stone or mosaic on exposed earthbag surfaces if you like (for example, the front of each terrace can be plastered and then decorated with tiles or bottles). Paint the interior of the gazebo or hang wind chimes. Since this prototype is also a proof-of-concept, you might set up sensors (thermometer, humidity gauge) in the space to record how stable the conditions are — this data can inform the full-scale design. The interior should now look like a sunken oasis: pond in the middle, a winding path around it, garden beds on terraces, and a small tower or gazebo structure as a focal point.

3. Structural & Environmental Considerations

Building a subterranean dome base comes with special structural and environmental factors to ensure it lasts long and remains comfortable. Key considerations include keeping water out, managing soil pressure, maintaining air quality, and planning for future loads.

Drainage and Moisture Control

Controlling water is paramount for an earthbag structure, especially one built partially underground. Drainage features should already be in place (gravel trench, drain pipes, etc.) but ongoing vigilance is needed. The surrounding soil should be contoured to channel rainwater away from the dome. If the pit is below grade, create swales or berms around the site to divert surface runoff. The French drain under and around the foundation will carry away moisture — ensure its outlet remains clear of debris. You might even add a dry well or soakaway pit at the drain outlet to dissipate water.

All earth contact surfaces need waterproofing. We wrapped the exterior of the earthbag walls in heavy plastic during construction​

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, and this will protect the bags from any seepage. If you notice damp spots inside after rain, address them: for example, add more drainage or apply additional waterproof coating on the outside. In humid or rain-heavy regions, it’s worth considering an external coating such as an elastomeric sealant or bitumen on the buried walls, but only after the earthbags have fully dried and cured. Remember, earthbags are extremely durable when kept dry, but prolonged exposure to moisture can weaken earthen fill or rot any natural fibers. Thus, multiple layers of moisture defense are wise — gravel drainage to relieve hydrostatic pressure, membranes to block water, and good site grading​

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Inside the dome, manage condensation. The pond will evaporate water into the air, which is great for plants but could cause condensation on cooler walls. A vapor barrier layer on the inside of the outer walls (under the plaster) can prevent moisture from penetrating the earthbags. Also, using lime in the interior plaster can help regulate humidity (lime plaster breathes and is mold-resistant). If condensation becomes an issue, you may need to increase ventilation or add a small dehumidifier when the space is closed off.

Erosion control is also part of moisture control. The landscaped terraces should be planted or protected so that heavy rain doesn’t wash soil into your beautiful interior. Until plants take root, lay jute netting or mulch over exposed soil. The greenery will eventually act as a living erosion control mat, and their roots will help suck up excess water.

In summary, keep water away from the structure as much as possible. With proper drainage and waterproofing, an earthbag dome can be essentially flood-proof and erosion-proof, as earthbag buildings have been used successfully even for underground houses and survived floods​

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. The effort put into french drains, gravel bags, and plastic liners will pay off in longevity.

Airflow and Ventilation

A below-grade dome can easily become stagnant or musty without planning for airflow. From the start, we’ve integrated ventilation ducts (earth tubes) and a gap for rising hot air. While the prototype is open or only partially covered, natural breezes and the open top will ventilate it. But once you add an upper dome or roof, you need to ensure fresh air exchange.

Passive ventilation techniques are ideal to minimize mechanical needs. We placed earth tubes which can cool and supply fresh air by convection. As warm air inside rises (especially when the full dome is added), it will create a slight vacuum that draws cool air in through those underground tubes​

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. To make this effective, design a high point in the dome (e.g. a vent at the apex or a vented cupola/tower) for hot air exhaust. In the final structure, the internal tower could act as a ventilation chimney if it’s designed with openings at the top. For now, you can simulate this by having a tall vent pipe that extends up from the interior to above ground level, allowing hot air to escape. Tip: Put screened openings near the top of the prototype (even if it’s a temporary cover) — in Owen Geiger’s earthbag buildings, small screened vents near the roof line let the hottest air out while keeping bugs out​

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Additionally, consider cross-ventilation. If there are multiple entry or window openings around Layer 1, ensure you can open them to get air flowing through. The spiral design is essentially one continuous space, but you could incorporate a short ventilation tunnel that connects the inner pit to the outside at a low level (besides the earth tubes). This could be as simple as a 8-inch PVC pipe running straight out from near the floor of the dome to daylight on a lower hillside — cool air will tend to come in low, while hot goes out high.

Cooling: The earth itself provides thermal cooling (and heating) thanks to its mass. The floor and walls, being mostly earth, even out temperature swings. We also added the pond as thermal mass — water is excellent at absorbing heat during the day and releasing it at night​

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. This will mitigate temperature extremes. For a 20′ tall dome, you have a lot of air volume, which helps prevent quick overheating. Still, in hot weather, the interior should be vented in early morning or late evening to expel heat. The earth tubes we installed can cool incoming air by 10–20 °F before it enters​

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, which is significant in summer. You might augment this by adding a small solar-powered fan to one of the tubes to actively pull more air in during very hot days, though in many cases the convection will work on its own.

Heating: In a cold climate, underground construction holds heat well. If you close off the top, the dome will retain warmth — perhaps too much humidity though. To avoid dampness in cold times, you might occasionally need to run a heater or dehumidifier, or simply open vents on dry winter days. In the finished biodome, the balance of humidity and temperature will likely be maintained by the greenhouse effect of the dome cover plus the thermal mass. The prototype lets you experiment with this. You could try a cold-night experiment: cover the pit with a tarp or temporary roof and see how the temperature and humidity behaves overnight, adjusting ventilation accordingly.

In essence, treat this layer like a big lung of the building — design it so it can inhale fresh air and exhale stale air with minimal energy. By combining the strategies above (earth tube intake, high exhaust vent, cross-breeze openings, water for humidity, earth for thermal mass), you create a passive climate control system. Many of these ideas derive from earthship design and subterranean greenhouse design, proven in various climates to maintain comfort naturally​

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Future Scalability and Adaptability

Since this prototype is the foundation of a larger biodome, we intentionally built it with future expansion in mind. Several features make it adaptable for the next phases:

• Structural Anchors: We embedded rebar and left attachment points at the top of the earthbag walls. These can be used to secure the next layer’s structure. For instance, if the next layer is an above-ground dome (perhaps an aircrete or wooden geodesic dome), you can bolt it to the bond beam or to those protruding rebars. The earthbag foundation is strong and can bear substantial load, but connecting the upper structure firmly is key. A continuous bond beam or ring at the top of Layer 1 ensures that it can handle any outward thrust from a dome on top​
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• . Essentially, Layer 1 acts as a ground-level retaining wall and foundation for whatever comes next.
• Internal Tower Extension: The gazebo/internal tower we built can be extended vertically. In the full-scale design, this might become a central column that goes all the way up, perhaps reaching the top of the biodome. Make sure the tower’s foundation is robust (if not, you can retrofit by pouring concrete around the base or adding more supports before building up). If it’s built strong enough, you could later frame a staircase around it connecting to an upper floor, or use it to support platforms. The prototype’s tower thus serves a dual purpose: it’s a nice feature now and a supporting spine for the future (it could carry part of the weight of a roof or upper stories, reducing the span for the dome cover).
• Modular Utilities: We routed conduits and pipes with extra capacity and accessible ends. When expanding, you won’t need to tear up Layer 1 to add wiring or plumbing — just pull new wires through the existing conduit to power new systems (lights, fans, sensors) in the upper dome. The water line stub can be hooked to a pump or an external source to feed irrigation in higher planters. The drainage we installed can handle additional water (like condensation or extra runoff from upper layers) by channeling it down to the pond or out the perimeter drain. By over-sizing pipes slightly and leaving pull cords in conduits, you’ve “future-proofed” the utilities. Even the earth tubes for ventilation can be extended or connected to upper vents easily, because their terminus is already in place inside this layer.
• Adaptable Interior: The way we’ve landscaped Layer 1 allows flexibility. The garden beds on terraces can remain as is for a lush ground floor, or they could be reconfigured into living spaces if needed (for example, one could pave a terrace to make a seating area or lab space in the future biodome). The pond, as built, can integrate into an aquaponic loop — you could add a small pump to circulate water to hydroponic grow beds that might be set up in the upper dome, then drain back to the pond. Knowing this, we placed it centrally. If plans change and you decide you need that area for something else, the pond could be converted (drained and filled) into a solid floor or foundation for a different feature — the liner can simply be removed and you already have a waterproof pit that can be used for storage or a basement. That’s the advantage of earthbags: they are non-toxic and flexible, so alterations later (like adding a doorway through a bag wall, or attaching a new wall) are feasible with some labor.
• Load-Bearing Capacity: Earthbag walls have a high compressive strength (they’ve been used to support roofs, even multiple stories)​
• instructables.com
• . Our terraced design distributes loads well into the ground. When adding upper layers, vertical load from those layers will bear down mostly at the perimeter. We should keep heavy new loads aligned over the existing walls or add supports accordingly. Fortunately, the circular/spiral layout is inherently strong (arches and circular forms naturally channel loads). The prototype can likely support a dome or second story as-is, but if an engineer’s review suggests more reinforcement, it’s easy to add: for example, you could hammer additional rebar down through all bag courses now or even pour a concrete bond beam with rebar that ties into the next layer. Think of Layer 1 as a basement; you can always line the inside with a masonry or concrete retaining wall later if extreme loads or code requirements demand, but in most cases the properly built earthbag walls will be more than sufficient.
• Openings and Connections: Plan where stairs or ladders will connect to go up to layer 2. Perhaps the spiral path continues upward as a ramp when you extend the dome — you might need to leave a segment of the upper wall unbuilt now (or lightly built) so you can break through later to make a passage. For instance, if the main entrance of the full biodome will be at ground level into Layer 2, you’ll need a way to get from that entrance down into Layer 1 (or vice versa). The prototype’s design should anticipate that: maybe the spiral ramp is aligned such that it will meet an entry door on the outer dome. It’s useful to sketch a section of the full dome to see how Layer 1 and Layer 2 connect (staircases, ladders, elevators?). With that in mind, leave placeholders: e.g., leave some rebar sticking out where a future concrete stair might anchor, or keep an area of the berm un-planted where you might dig an opening later. Since this is a DIY iterative build, having these little foresights will save time when transitioning to the next build phase.

In summary, Layer 1 is built as a permanent substructure of the future biodome. We aren’t doing anything temporary or throw-away — every element is serving a long-term purpose. The materials (earth, gravel, plastic, rebar) are all going to be encapsulated and used in the final design. When it’s time to expand, it should be seamless: you’ll build upon this foundation without needing to rebuild it. The prototype can be enjoyed on its own now and is essentially “phase one” of the full project.

4. Future Expansion Plan

With a successful prototype in place, the next steps involve integrating this Layer 1 foundation into the full-scale biodome structure. Here’s how to transition smoothly:

• Adding the Dome Superstructure (Layer 2): The full biodome likely includes a large dome or shell that encloses the environment. To expand, you will construct this dome on top of (or around) the existing pit. Many options are available — you could build a geodesic dome frame from metal or wood that sits on the perimeter of Layer 1, or create an aircrete or masonry dome that springs from the earthbag walls. Thanks to the bond beam and anchors we prepared, mounting a dome frame will be straightforward. For example, if using a geodesic kit, you can bolt its base connectors into the embedded bolts on the earthbag wall. If building an aircrete dome, you’ll pour it in place using the Layer 1 wall top as the form’s base. Remember the note from the Djibouti eco-dome: when finished it was 21 feet tall​
• commons.wikimedia.org
• – our 20′ target is right in line with such real-world examples. So proceed confidently knowing your base can handle it. As you build Layer 2, keep the weight distributed evenly and utilize the central tower if needed for support (you might temporarily or permanently brace the growing dome structure against that tower).
• Enclosure and Roofing: Once the above-ground dome (Layer 2) is up, Layer 1 becomes an enclosed ground floor. At that point, tie in the waterproofing between layers. For instance, if the new dome has a membrane or shell, overlap it with the waterproof barrier of Layer 1 so there’s continuous protection. Any gap between the earthbag wall and the dome frame should be sealed (using foam, mortar, or fabric) to prevent water or air leaks. Essentially, you create one unified envelope from the top of the new dome down to the base of Layer 1. If the full biodome has multiple layers (say Layer 3, a second floor or smaller dome on top), the process is similar: each subsequent layer builds on the previous, with appropriate structural support and moisture sealing.
• Access and Circulation: During expansion, you’ll establish formal entrances and exits. Possibly, you will create an entry tunnel or door at ground level that leads into Layer 1 or 2. If the main door is going to be in the new above-ground portion, then install a staircase or ramp from that entry down to the sunken garden (Layer 1). You might use the spiral ramp that already exists — continue it upward to meet the new entrance. Or build a new staircase attached to the inner wall. The internal tower can now be outfitted with a spiral staircase around it, reaching up to a mezzanine or the dome’s observation deck. Since the tower was built sturdy, you can extend its posts or add new sections to reach higher. Consider if you want a floor or loft at the top of Layer 1 (for example, a transparent floor to look down into the pond, or a solid floor to create rooms). The expansion allows you to put in these architectural features. The prototype garden might remain open through the height of the dome, or you may divide levels — the design is flexible.
• Systems Integration: In the full biodome, you’ll likely have more complex systems (solar power, automated ventilation, heating elements, etc.). Integrate them using the groundwork from Layer 1. The electrical conduit you placed can be extended into the new walls — pull wires through to add outlets and lighting in the new dome. You can install grow lights, climate sensors, or even a small climate-control computer, all drawing power through those conduits. The water pipes can connect to rainwater harvesting from the dome or to a pump that circulates water between the pond and higher hydroponic beds (creating an aquaponics system where fish in the pond fertilize plants and plants filter the water). The drainage we’ve set will continue to function — if the upper dome has condensation dripping down, the French drain or pond will catch it. You might add gutters at the base of the dome to channel water down to the pond or out to the drain as needed. Ventilation shafts from Layer 1 can connect to vents in Layer 2’s dome shell, promoting the stack effect for the whole structure.
• Gradual Transition: It’s possible you won’t build the entire biodome at once — maybe Layer 2 is added, then some time later an even larger Layer 3 or outer shell. Each addition should be designed to not disturb the previous work. Our prototype is robust enough to be left as-is until you’re ready for the next step. When working on Layer 2, protect Layer 1’s interior (cover the pond, perhaps put tarps over the garden beds) to avoid construction debris or weather harming them. Many builders sequence like this: finish the subterranean parts first (as we did), then erect the shell, then do finish work inside. We’ve essentially done the first two phases — interior finish of Layer 1 can either be done now or after the shell is up, depending on convenience. There is no need to tear anything down; the prototype is literally part of the final structure.
• Scalability: If the full biodome plan includes expanding horizontally (say adding more rooms or connecting to other domes), the Layer 1 prototype can act as a hub. You could leave a section of the perimeter earthbag wall un-planted and un-plastered where a future doorway could be knocked through to a tunnel or corridor. The earthbag wall can be cut (with some effort) for new openings — you’d remove bags and trim barbed wire, then frame the opening with a reinforced concrete or wooden frame. It’s done in earthbag construction for adding doors/windows. So even if your biodome design evolves, you can modify this base. The key point is that the adaptability is built-in: earthen construction is forgiving. Unlike a strict concrete bunker, you can carve, add, or adjust earthbag structures relatively easily with hand tools and additions.
• Long-Term Vision: Over time, the Layer 1 dome foundation might transition from an outdoor garden to an indoor one (once enclosed), perhaps becoming a tropical atrium at the center of your biodome. The pond could host fish year-round with the stable temperatures. The internal tower could eventually support solar panels or a small wind turbine if extended above the dome (conceivable as a sort of “power tower”). When designing the final additions, think of how Layer 1’s features can be optimized: e.g., the pond as a thermal battery to help heat the dome in winter​
• growingspaces.com
• , the earth walls as a natural temperature regulator (thermal mass), the plants as air purifiers. The prototype you built is not just a foundation of concrete — it’s a living foundation that will actively contribute to the biodome’s ecology and structure.

To conclude the expansion plan: as you build upward and outward, always connect back to this prototype. It’s your literal ground truth. Treat Layer 1 as the core of the biodome — structurally (it bears weight), functionally (it hosts the water and some agriculture), and as a reference for conditions (you’ll know from the prototype how humid or warm it tends to be, informing how you design ventilation and heating for the whole dome). By following this guide, your DIY prototype is clear, solid, and ready for the next chapter — the fusion into a full-scale, self-sustaining biodome that you can live in or grow in for years to come.

Sources:

instructables.com

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en.wikipedia.org

– Earthbag foundation preparation (trench to subsoil and gravel footing)

instructables.com

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en.wikipedia.org

– Gravel-filled earthbag courses and barbed wire reinforcement for sturdy walls

reddit.com

– Example of waterproofing earthbag walls with plastic, using aircrete and gravel for drainage, and running conduit through bags

growingspaces.com

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growingspaces.com

– Pond inside greenhouse acts as thermal mass, adding humidity and supporting aquatic life (Growing Spaces domes)

earthship.com

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earthship.com

– Earth tubes (in-ground ventilation pipes) provide passive cooling up to 10–20 °F, with no electricity needed (Earthship design)

earthbagbuilding.wordpress.com

– High ventilation openings in dome structures allow hot air to escape, aiding passive cooling

commons.wikimedia.org

– Real-world “eco-dome” (earthbag) example: 21-foot high earthbag dome structure (showing feasibility of height)

en.wikipedia.org

– Use of bond beam on earthbag walls to support traditional or additional structures above.