Greenhouse BioDome

A 6-metre dome greenhouse built from eucalyptus poles and greenhouse plastic. Two people with hand tools can raise one in a long weekend for under €300. It’s the easiest way to start building with eucalyptus — and the frame you build here can later become a permanent insulated dwelling if you choose to take it further.

6mDiameter

28m²Floor Area

2–3 daysBuild Time

€150–300Budget

How It Works

The dome is made from 14 long, flexible eucalyptus poles — each one spanning the full 6-metre diameter. They’re paired into 7 arches that cross at the top, forming a shape called a catenary curve (the natural shape of a hanging chain, flipped upside down). You don’t need to force the poles into a precise mathematical shape. You bend each pole by hand during installation, and gravity does the rest — the poles find their own curve and the structure stays in compression, which is what timber does best.

Five horizontal wattle rings woven between the arches lock the frame together. Then greenhouse plastic drapes over the whole thing, lashed down with battens and rope. That’s it — poles, rings, plastic.

What you need:

• Site: A roughly level clearing, 7m across minimum (6m dome + workspace)
• People: 2 (one to hold, one to lash — the poles are long)
• Tools: Drawknife or machete, shovel, wire cutters, tape measure, spirit level, scissors or utility knife
• Time: 1 week of pole prep, then 2–3 days of building

Before the Build Weekend

Start pole preparation at least one week before you plan to build. The borax soak takes a minimum of 72 hours.

1. Harvest poles

   You need 16 arch poles (14 + 2 spares), about 30 ring poles, and 3 door frame posts. Select young, straight eucalyptus trees — 5–8 years old gives the best flexibility for bending. If you’re clearing eucalyptus from your land, see the Harvesting Guide for details on selecting trees and treating stumps to prevent regrowth.

   • Arch poles: 8–10cm butt diameter, ~11.6m length, E. globulus (blue gum)
   • Ring poles: 5–7cm diameter, 2–4m length
   • Door posts: 8–10cm diameter, ~2m length

   Green Poles Only

   Eucalyptus must be green — harvested within 2 weeks of use. Dry eucalyptus is brittle and will snap during bending. Select the youngest, straightest trees at 5–8 years old. If poles have been cut more than a few days ago, soak them in water for 48–72 hours before use to restore flexibility.

2. Debark within 48 hours

   Strip all bark with a drawknife or flat-blade scraper. Work from butt to thin end, following the grain. Bark left on traps moisture and accelerates rot — debarked poles last years longer.

3. Borax soak — 72 hours minimum

   Submerge all poles in a borax solution to protect against termites, wood-boring beetles, and fungal rot — the three things that kill untreated eucalyptus in Portugal within 5–10 years.

   Recipe: Mix 12.5kg borax + 8.3kg boric acid per 1,000 litres of water (~2% solution). A simple soaking trough can be made from two sawhorses with U-shaped sheet-metal channels lined with heavy-duty plastic sheeting, held together with ratchet straps. See the Treatment Guide for the full trough design and recipe.

   Weight the poles below the surface with concrete blocks or heavy stones. Soak for a minimum of 72 hours — longer is better.

4. Score arch poles for bending

   Using a drawknife or machete, score shallow cuts (1–2mm deep) every 15cm along the outer face — the face that will be on the outside of the curve when bent. Concentrate scoring on the middle third of the pole, where the bend will be tightest. This relieves tension in the outer wood fibres so the pole bends smoothly rather than cracking.

   

   Pole scoring detail: shallow cuts every 15cm on the outer face, concentrated in the middle third where the bend is tightest

5. Sort and pair

   Sort all 16 arch poles by butt diameter. Pair them so each arch has two poles of similar size. Number each pair 1–7 (plus 2 spares). Within each pair, mark the poles so butt ends go on opposite sides of the dome — this balances the taper across each arch (the thick end of one pole sits beside the thin end of the other at each foundation point).

Day 1 — Foundation

Gravel-filled postholes keep the pole bases out of standing water and allow drainage — the simplest foundation that works. Each posthole takes about 15 minutes.

1. Mark the circle

   Drive a stake at centre. Tie a 3m string to it and scribe a 6m diameter circle on the ground. Walk the circle and clear any rocks, roots, or debris.

2. Mark posthole positions

   You need 15 postholes evenly spaced around the circle (every ~1.26m). The easiest way: mark north, then every 24 degrees around (use a protractor or the 15-peg string method — tie 15 equal-length strings from the centre and space them by eye, then adjust until the gaps look even). Skip one position for the door — choose the side that faces your access path or prevailing sun.

   

   Foundation plan view: 15 postholes at ~1.26m spacing, door opening, and ground stake positions

3. Dig postholes

   Each hole: 30cm deep, 20cm wide. If your soil is very clay-heavy or waterlogged, go 40cm deep and add an extra 10cm of gravel at the bottom.

4. Fill with gravel

   Drop a flat stone at the bottom of each hole (this is the bearing surface — keeps the pole end off raw earth). Fill with 15cm of gravel or crushed stone. The pole butt will sit on this gravel bed, with more gravel packed around it after the frame goes up.

5. Install door frame

   At the door opening, set two vertical posts (8–10cm diameter, ~2m above ground + 40cm buried) into postholes on each side of the gap. Pack firmly with gravel. Lash a horizontal crosspiece at ~2m height between them with galvanized wire. This is your door frame.

6. Drive ground stakes

   At each posthole position, drive a 60cm rebar stake or hardwood stake vertically into the ground, 20cm from the hole on the outside of the circle. These stakes will anchor the pole bases against wind uplift once the frame is up.

Posthole cross-section: flat stone bearing, gravel packing, pole with optional plastic wrap, and ground stake for uplift resistance

Level Ground

The dome frame is forgiving of slightly uneven ground — the catenary curve adjusts naturally. But if your site slopes more than ~20cm across the 6m diameter, terrace the uphill side with a shallow cut so the postholes are roughly level.

Day 2 — Frame and Wattle

This is the most physical day. Two people can raise all 7 arches and install the wattle rings in a full day of work.

Raising the Arches

Each arch is made from two poles that span the full diameter of the dome, crossing at the top. You bend them by hand during installation — no bending forms, no jigs. The poles are green and scored, so they flex into a smooth curve and hold that shape as they dry in place.

Raising the arches: first pair forms a self-supporting arch, second pair at 90° makes it freestanding, all 7 pairs wire-wrapped at the crown

1. First pair

   Take the first pole of Pair 1. Set its butt end into a posthole. Two people walk the pole up from the other end, bending it live into an arc as they go — the pole curves naturally under its own weight. One person holds the pole at the apex while the other sets the thin end into the opposing posthole across the diameter.

   Now install the second pole of Pair 1 from the opposite side — its butt end goes into the posthole next to where the first pole’s thin end landed, and its thin end reaches the posthole next to the first pole’s butt end. This way the thick and thin ends alternate around the perimeter.

   Lash both poles together at the crown with galvanized wire, wrapping tightly. The completed arch is self-supporting.

2. Second pair (perpendicular)

   Install the second pair at 90 degrees to the first, using exactly the same technique. Where the four poles cross at the apex, lash them together with galvanized wire. The two arches now stabilise each other — the structure is freestanding.

3. Remaining five pairs

   Install five more pairs at even spacing around the circle, skipping the door position. Each new pair is walked up, bent live, and lashed to the existing poles where they cross at the crown. The structure gets more rigid with each pair added.

4. Secure the crown

   Once all 7 pairs are up (14 poles total), wrap the entire crown crossing with galvanized wire in a tight spiral. This zone — roughly 30cm across, where all 14 poles overlap — is the structural keystone of the dome. Wrap it well.

5. Lock pole bases

   Pack more gravel tightly around each pole butt in its posthole. Then wire-lash each pole to its adjacent ground stake for wind uplift resistance. Optionally, wrap the bottom 30cm of each pole in a plastic bag before packing the final gravel — a cheap moisture barrier that adds years of life.

Check the Shape

Before adding wattle, stand back and look at the dome from all sides. It should be roughly symmetrical. Measure the height at centre — it should be close to 4m. Adjust pole positions in their postholes if needed. Once wattle rings go on, adjustments become difficult.

Wattle Rings

Wattle is one of the oldest building techniques — horizontal poles woven alternately inside and outside of vertical supports. Here the arch poles are the verticals, and you weave horizontal ring poles between them to create a lattice. Five rings are enough to support greenhouse plastic and prevent billowing in wind.

Wattle ring weaving: ring poles alternate inside and outside of each arch pole — basket-weaving at building scale

1. Harvest ring poles fresh

   Cut ~30 ring poles (5–7cm diameter, 2–4m length) the same morning you plan to weave them. Green eucalyptus becomes too stiff to weave within 24–48 hours in Portuguese summer sun.

2. Install 5 horizontal rings

   Starting at about 60cm above ground level, weave a ring pole horizontally around the dome, alternating inside and outside of each arch pole as you go. Where a ring pole runs out, overlap the next one by 30cm and wire-lash the join. Space the 5 rings roughly evenly — about 60cm apart vertically. The highest ring sits about 60cm below the crown.

3. Check ring tension

   Each ring should be snug against the arch poles, not loose. Push on the wattle between rings — it should flex slightly but not flap. If any section feels loose, add a short extra ring pole in that zone.

Day 3 — Plastic and Ventilation

The fastest day. Two people can cover the dome in greenhouse plastic, frame the door, and set up ventilation in half a day.

Materials

• Greenhouse plastic: 150μm (6mil) UV-stabilised polyethylene. Buy a single roll — standard sizes are 8m wide × 25–50m long. You need roughly 2 pieces, each about 8m × 8m, to cover the dome with overlap.
• Greenhouse repair tape: UV-resistant poly tape for joining sheets and patching.
• Twine or poly rope: ~100m for lashing battens.
• Split-pole battens: ~20 pieces of thin (2–3cm) eucalyptus or other wood, 1–1.5m long. Split from offcuts — these press the plastic against the wattle rings.

Covering the Dome

1. Cut two sheets

   Roll out the plastic on flat ground. Cut two pieces roughly 8m × 8m each (adjust if your roll is wider or narrower — you need enough to drape from the crown to ground level on each side, with 50cm extra at the base for anchoring).

2. Drape the first sheet

   Choose a calm day — wind is your enemy. Drape the first sheet over the dome from the crown, covering one half. Let the excess pool at the base. The sheet should extend past the crown by ~1m to overlap with the second sheet.

3. Drape the second sheet

   Drape the second sheet over the other half, overlapping the first sheet by at least 50cm at the ridge (the line running over the crown). Tape the overlap with greenhouse repair tape — run a continuous strip along the full length of the join.

   

   Two-sheet draping: sheets overlap by at least 50cm at the ridge, taped along the full join, excess weighted at the base

4. Lash to wattle rings (sandwich method)

   At each of the 5 wattle ring levels, lay a split-pole batten over the plastic on the outside, pressing it against the wattle ring underneath. Lash the batten to the ring with twine, threading through gaps in the plastic as little as possible. The batten sandwiches the plastic between itself and the ring — no staples or punctures needed. Work your way around the dome at each ring level.

   

   Sandwich lashing detail: batten presses plastic against the wattle ring, held by twine — no punctures needed

5. Anchor the base

   You have two options:

   • Trench method: Dig a shallow trench (15cm deep) around the base, lay the excess plastic into it, and backfill with soil. Permanent, secure, but harder to open for ventilation.
   • Weight method: Fold the excess plastic under and weight it with a continuous line of stones or sandbags. Easier to lift sections for ventilation. This is the recommended method.

6. Frame the door

   Cut the plastic at the door opening, leaving 30cm extra on each side. Fold the edges over and tape them to themselves for reinforcement (raw-cut plastic tears easily). Create a door flap: cut a piece of plastic 20cm wider than the opening and 20cm taller. Tape or lash it across the top of the door frame so it hangs down as a curtain. Weight the bottom edge with a thin pole sewn into a fold — this keeps it closed in wind but lets you push through.

Ventilation

A sealed plastic dome will overheat on any sunny day. You need cross-ventilation.

Ventilation airflow: cool air enters low through the roll-up vent, hot air rises and exits through the door and apex

• Roll-up base: On the side of the dome opposite the door (the leeward side in your prevailing wind), leave the base plastic unanchored for a 2–3m section. Roll it up to waist height on warm days and secure with clips or ties to the lowest wattle ring. This creates a low inlet; hot air rises and exits through the door or an apex vent.

• Apex vent (optional): At the crown, cut a 30cm diameter hole in the plastic. Tape the edges for reinforcement. Cover with a small cone of plastic on a short post (a pot lid on a stick) to shed rain while allowing hot air to escape around the edges. Not essential if you use the roll-up base + open door method, but it improves airflow significantly on still days.

• Door: On hot days, tie the door flap open. Combined with the roll-up base on the opposite side, this gives you through-ventilation across the full diameter.

Bill of Materials

Item	Qty	Specs	Est. Cost
Eucalyptus arch poles	16 (14 + 2 spares)	8–10cm dia, ~11.6m, green	€0–50
Eucalyptus ring poles	~30	5–7cm dia, 2–4m, green	€0–15
Door frame posts	3	8–10cm dia, ~2m, treated	€0–10
Borax + boric acid	10kg	Technical grade	€15–25
Gravel / crushed stone	0.3m³	For postholes	€10–20
Greenhouse plastic	~130m²	150μm UV-stabilised polyethylene	€40–80
Greenhouse repair tape	1 roll	UV-resistant poly tape	€10–15
Galvanized wire	50m	3mm diameter	€25–35
Twine / poly rope	100m	UV-resistant preferred	€10–15
Ground stakes	15	60cm rebar or hardwood	€15–25
Total			€125–290

Where to Buy in Portugal

• Greenhouse plastic: Agricultural supply stores (agro-pecuária) or Leroy Merlin/AKI. Ask for “plástico de estufa UV estabilizado, 150 microns.”
• Borax: Pharmacy or chemical supply. Ask for “bórax” or “borato de sódio” and “ácido bórico.”
• Galvanized wire: Any hardware store (ferragem). Ask for “arame galvanizado 3mm.”
• Gravel: Builders’ merchants or quarries (britagem). Ask for “brita” or “gravilha.”

Maintenance

Monthly: Walk the perimeter. Check that base anchoring is secure, no plastic has torn free from battens, and no wattle rings have come loose. Re-lash anything that’s shifted.

Seasonally: Before winter storms, check all wire lashings at the crown and pole bases. Tighten any that have loosened as poles dry and shrink (eucalyptus shrinks 4–8% radially in the first year).

Every 3–4 years: Replace the greenhouse plastic. UV-stabilised plastic lasts 3–4 years in Portuguese sun before it becomes brittle. Replacement is a two-person, half-day job — strip old plastic, drape new sheets, re-lash battens. Budget €40–80 each time.

What’s Next — Upgrading to a Permanent Dwelling

The Greenhouse BioDome is designed as the starting point of a larger journey. The arch frame, crown lashing, wattle rings, and door frame you’ve just built are the exact same skeleton used in the Standard BioDome — a fully insulated, weatherproof dwelling with a 25–35 year lifespan. When you’re ready to make that leap:

1. Remove the plastic

   Strip the greenhouse plastic. Reuse it as ground cover, pond liner, or on another structure.

2. Build the gabion ring foundation

   A gabion ring — stone-filled wire cages forming a 6m circle — replaces the gravel postholes with a proper foundation that includes integrated drainage. The existing postholes get absorbed into the gabion fill. This is the one component that doesn’t carry over directly, but you’re not demolishing anything.

3. Add vertical wattle infill

   Weave ~200 vertical infill poles between the existing horizontal rings to create a dense lattice. This provides the substrate for the insulating wall layers that follow. See the Wattle Weave guide.

4. Build up the insulated shell

   The Standard BioDome build guide picks up from here: light straw-clay insulation, a waterproof EPDM membrane, stone skirt exterior, lime plaster interior. The full conversion adds 4–5 weeks of work and €1,500–5,000 in materials — but you end up with a permanent home.

The best time to start the conversion is after 2–3 years, when the poles have fully dried and stopped moving. By then you’ll know the dome intimately — every quirk, every settling point — and the conversion will go smoothly.

Know the Limits

• Foundation: Gravel postholes give 10–15 years of pole protection. For a 30+ year dwelling, the gabion ring upgrade is essential.
• Treatment: The 3-step treatment (debark, borax, bend) is adequate for a 10–15 year greenhouse frame. Charring the pole bases and sealing with hot linseed oil — steps included in the full treatment protocol — extend the lifespan to 30–40 years.
• Plastic: Budget for replacement every 3–4 years (€40–80 per cycle).
• No thermal mass: This is a greenhouse, not a living space. Winter nights will be cold inside. Summer days will overheat without ventilation. Design your planting schedule accordingly.