The Regenerative BioDome: fire-resistant homes built from invasive eucalyptus
Part One: Universal Principles
Chapter 1: Why This Matters
Picture this: You're standing in what should be a diverse Mediterranean oak forest in Central Portugal—home to cork oaks, stone pines, wild olive, and strawberry trees humming with life. Instead, you're surrounded by a silent eucalyptus monoculture. The ground is bare. Nothing grows beneath these Australian invaders.
This is the reality across 26% of Portuguese forests—over 800,000 hectares conquered by Eucalyptus globulus, the Tasmanian blue gum.
- Drinks 20-30 liters of water per day (stolen from the watershed)
- Releases allelopathic chemicals that poison other plants
- Drops volatile oil-rich bark that turns landscapes into tinderboxes
- Acidifies soil and destroys beneficial microbes
- Creates biological deserts where rich ecosystems once thrived
The Radical Idea
What if the act of removing eucalyptus could produce something valuable? What if ecological restoration could be economically viable? What if "waste" biomass became functional architecture?
Enter the Regenerative BioDome—a permanent, fire-resistant home built from the very trees poisoning your land.
90% ecological restoration, 10% building project. You're not just constructing a home. You're healing a watershed, preventing wildfires, enabling native forest regeneration, and demonstrating that restoration can create real value.
How This Design Was Born
The BioDome concept emerged from a surprisingly humble beginning: a wattle fence. During a visit from family, we learned the traditional technique of weaving young eucalyptus poles into a fence to keep wild boars from our garden. As the weaving progressed, an experiment began—angling the poles at 45 degrees instead of the traditional 90. The structure became stronger, more dynamic.
From there, it was a small conceptual leap to imagine this trellis wrapping back on itself, forming a giant inverted wicker basket. This is biomimetic engineering: working with the material's nature rather than against it.
The Da Vinci Bridge: Understanding Reciprocal Framing
But wattle weaving is only half the story. The BioDome's roof uses a different structural principle—one that Leonardo da Vinci sketched over 500 years ago.
Around 1480, Leonardo designed a portable military bridge for rapid deployment. The genius was in what it didn't need: no nails, no rope, no fasteners of any kind. The structure holds itself together through reciprocal framing—each beam rests on the next, and the geometry locks them in place under load. The more weight you add, the stronger it becomes.
This principle—where each element both supports and is supported by its neighbors—is what makes the BioDome's roof possible. A spiral of rafters, each resting on the one before it, creates a self-supporting dome with no central post. The technique appears in 12th-century Buddhist temples (Todai-ji in Nara, Japan) and traditional roundhouses across cultures, but Leonardo's bridge remains the clearest demonstration of why it works.
Friends built this da Vinci bridge over our stream using eucalyptus poles. Standing on it, you can feel how the structure responds—how your weight presses the beams more firmly into their interlocking positions rather than pulling them apart. This is the same principle that holds the BioDome's reciprocal roof together, scaled up and arranged in a spiral.
Traditional roof construction requires either a central post (blocking your floor space) or heavy ridge beams and complex joinery. Reciprocal framing eliminates both. The roof supports itself, leaving the interior completely open—and it can be built with round poles that would be difficult to use in conventional construction. Perfect for eucalyptus.
The eucalyptus invasion presented itself not just as a problem to be solved, but as a building material waiting to be harvested. If fire is inevitable in Mediterranean landscapes, the wisdom of indigenous peoples who lived harmoniously with fire becomes relevant: build structures that are quick, cheap, and fire-resistant—from the very fuel that feeds the flames.
While eucalyptus is ideal for structural framing (posts, wattle poles, rafters, purlins), its tendency to warp and twist as it dries makes it unsuitable for precision millwork. Window frames, door frames, and mullions require dimensional stability for tight weatherseals and smooth operation. For these applications, use chestnut (Castanea sativa)—a native Mediterranean hardwood with excellent stability, natural rot resistance from high tannin content, and a long tradition of use in Portuguese building.
Chapter 2: Eucalyptus Harvesting & Eradication (EXPANDED)
This is an eradication project. The goal is to permanently kill the eucalyptus trees and enable native forest recovery. Every stump must be treated to prevent regrowth.
Cut-Stump Treatment (95-98% Success) — RECOMMENDED METHOD
This is the gold standard for eucalyptus eradication and is what we recommend for most builds:
Cut at Ground Level
Fell the tree as close to ground as possible using a chainsaw. Make the cut clean and horizontal.
Treat Stump Immediately
Within 15 minutes: Paint the entire cut surface with 25-50% glyphosate solution or 15-25% triclopyr solution. This is critical—eucalyptus tissue seals quickly, so you must apply herbicide before the stump begins to callus over. Use a brush and coat thoroughly.
Harvest Poles While Fresh
During the 1-2 week window while the wood is still workable, harvest poles from the freshly fallen tree. Young poles (2-7 year growth) are ideal for building.
Monitor for Resprouting
Check all treated stumps monthly for 12-18 months. Immediately cut and treat any resprouting shoots.
Success rate: 95-98%. Cost per tree: €0.50-2. Time commitment: One intensive harvest period, then monitoring.
Comparison Table of All Methods
| Method | Success Rate | Cost/Tree | Pros | Cons |
|---|---|---|---|---|
| Cut + Glyphosate Stump | 95-98% | €0.50-2 | Highest success, fast, uses tree for building | Requires immediate herbicide application |
| Cut + Triclopyr Stump | 95-98% | €1-3 | Works in wet conditions, excellent success | More expensive than glyphosate |
| Physical Removal | 100% | €20+ | Complete removal, no regrowth possible | Labor-intensive, expensive, requires machinery |
| Cut Only (No Treatment) | 5-10% | €0 | Cheap, fast | High regrowth, builds denser stump sprouts |
Herbicide Details
Glyphosate (Non-selective, most common)
- Active ingredient: Glyphosate isopropylamine
- Concentration for stump treatment: 25-50% (concentrated formulations, NOT lawn herbicide)
- How it works: Absorbed through freshly cut wood, translocates to roots, kills the whole plant
- Cost: €3-8 per liter (concentrated)
- Weathering: Rain-resistant after 1-2 hours
- Toxicity: Low mammalian toxicity, EPA approved, widely used
Triclopyr (Selective for woody plants)
- Active ingredient: Triclopyr butoxyethyl ester
- Concentration for stump treatment: 15-25%
- How it works: Absorbed through wood, acts like plant hormone causing uncontrolled growth, plant dies
- Cost: €8-15 per liter (concentrated)
- Weathering: Works even in wet conditions
- Toxicity: Moderate, more expensive but highly effective
Safety Protocols (Non-Negotiable)
- Gloves: Nitrile or latex (herbicides absorb through skin)
- Eye protection: Safety glasses or goggles
- Skin coverage: Long sleeves, long pants (prevent accidental exposure)
- Footwear: Closed-toe boots (protect feet from splashes)
- Respiratory protection: Not typically needed for stump treatment (low volatility)
Timing and Weather Conditions
- Best season: Late spring through autumn (trees are actively growing)
- Avoid: Heavy rain within 2 hours (wash off herbicide), extreme heat (speeds evaporation)
- Application time: Early morning or evening (cooler, minimizes volatility)
- Dry period needed: At least 1-2 hours after application before rain
Environmental Justification for Herbicide Use
Some builders resist herbicides on principle, preferring "organic" methods. However, for eucalyptus eradication at landscape scale, herbicides are the most environmentally responsible choice:
- Landscape health: Without herbicide treatment, eucalyptus resprouting creates denser, harder-to-remove thickets. Multiple years of cutting (without treatment) causes more disturbance than one chemical application.
- Herbicide impact: Glyphosate and triclopyr are broad-spectrum (kill most plants) but break down rapidly in soil. Concentrations used for stump treatment are highly localized (applied to stumps, not broadcast).
- Cost of alternatives: Physical removal (machinery, labor) causes massive soil compaction and erosion. Chemical spot treatment is gentler on soil.
- Permanence: 95-98% success with chemical treatment means native forest can establish. Repeated cutting without herbicide means eucalyptus keeps coming back for decades.
Chapter 3: Materials Overview
Combined Materials Table for All Three Designs
| Material | Standard (55m²) | Terraced (24m²) | Solar Pod (29m²) |
|---|---|---|---|
| Eucalyptus poles (trees) | 180-300 | 90-150 | 180-250 |
| Clay soil (m³) | ~15 | ~8-10 | ~12 |
| Sharp sand (m³) | ~10 | ~6-8 | ~8 |
| Straw (bales) | ~30 | ~20 | ~25 + insulation |
| Granite (m³) | 15-20 | 8-12 | 12-15 |
| Gabion mesh (linear m) | 60 | 40 (arc) | ~40 |
| EPDM liner (m²) | 80 | 50 | 50 |
| Budget Range | €5-8k | €3-5k | €8-18k |
Standard BioDome: Minimal €3-4k, Realistic €5-6.5k, Comfortable €7-8.5k
Terraced BioDome: Minimal €2.5-3.5k, Realistic €3.5-4.5k, Comfortable €5-6k
Solar Pod: Minimal €4.5-5.5k, Realistic €8-12k, Comfortable €14-18k (solar is 50-60% of cost)
Chapter 4: Pole Treatment Protocol
The 5-step process is identical across all three designs and is absolutely non-negotiable. Untreated eucalyptus fails in 5-10 years. Properly treated timber lasts 30-50+ years.
Skip pole treatment and your building will be colonized by carpenter ants within 3 years. Follow this protocol and your timber will last for generations.
Debark Within 48 Hours
Remove bark immediately after felling while wood is fresh. Use a drawknife or scraper. Bark traps moisture and prevents preservative penetration. Expose bare wood completely.
Borax Soak (72+ Hours)
Mix borax and boric acid in ratio 12:8:80 (borax:boric acid:water by weight). Submerge poles completely—they float, so weight them down. Minimum 72 hours; longer (up to 2 weeks) is better. This penetrates sapwood and creates a toxic barrier against insects and fungi.
Dry 2-3 Weeks Under Cover
Stack treated poles on raised supports in a shaded, well-ventilated area. Protect from rain. Air circulation is essential—poles will mold in a closed space. Stack with spacers between layers.
Char Bottom 50cm
Before installation, lightly torch the lower 50cm of each pole (embedding portion) to char the surface. This provides additional rot resistance where pole meets soil/moisture. Don't burn deeply—just darken the surface to 3-5mm depth.
Seal with Hot Linseed Oil
Heat linseed oil to 60-70°C (warm to touch but not steaming). Brush on all pole surfaces. The oil hardens over 2-3 days and waterproofs the wood while remaining breathable. Reapply every 5-10 years.
Chapter 5: Wall Infill: Light Straw-Clay
Why Light Straw-Clay?
Traditional cob (dense clay-sand-straw mixture) works well for monolithic walls, but presents challenges when used as infill between a wooden frame—especially with eucalyptus poles that shrink 5-8% as they dry over the first year.
Cob is rigid and heavy (~1,800 kg/m³). When eucalyptus poles shrink and shift during drying, cob cracks at the pole junctions—sometimes severely. Repairs are time-consuming and the cracks often return.
Light straw-clay solves this by reversing the ratio: instead of clay with straw reinforcement, it's straw with clay coating. The result is a lightweight (~400 kg/m³), flexible infill that:
- Absorbs frame movement internally rather than cracking
- Dries faster (4-6 weeks vs 2-3 months for cob)
- Easier to repair (stuff more straw into gaps)
- More forgiving to mix (less skill required for consistency)
- Reduces load on frame (1/4 the weight of cob)
The Recipe
| Ingredient | Description | Purpose |
|---|---|---|
| Straw | Loose, long-fiber (wheat, rye, or rice straw) | Bulk material—creates insulation and structure |
| Clay slip | Clay + water to thick cream/yogurt consistency | Coating—binds straw, provides fire resistance |
No sand. Unlike cob, light straw-clay uses pure clay slip without aggregate. The straw provides all the structure.
Making Clay Slip
Soak Clay Overnight
Put clay soil in a container, cover with water. Let sit 12-24 hours to fully hydrate and break down clumps.
Mix to Yogurt Consistency
Stir vigorously (a paint mixer on a drill works well). Add water until the slip coats your hand and drips off slowly—like thick yogurt or heavy cream.
Strain if Needed
If your clay soil has stones or debris, strain through a coarse screen. Pure clay slip coats straw evenly.
Coating the Straw
Toss Straw in Slip
Work in manageable batches. Toss loose straw into slip and turn it with your hands or a pitchfork until all fibers are lightly coated. The straw should glisten but not drip.
Don't Saturate
More slip is NOT better. Saturated straw takes longer to dry and loses insulation value. Every fiber should be coated, but the straw should still feel like straw—not like wet clay.
Packing the Wall Cavity
- Work between wattle poles in 15-20cm lifts
- Pack coated straw firmly into the cavity
- Tamp with a flat board or your fist—compress to remove large air pockets
- Don't over-compress (you want insulation value, not density)
- Continue until cavity is filled to the next wattle level
- Final wall thickness: 35-45cm (slightly thinner than cob is acceptable due to better insulation value)
Tamp firmly but not aggressively. You want the straw to hold together and fill gaps, but over-tamping crushes the straw fibers and reduces insulation. The packed wall should feel springy, not solid.
Drying Time
- Per 15cm depth: 1-2 weeks to dry through
- Total wall drying: 4-6 weeks (much faster than cob due to porosity)
- Test for dryness: Push a thin stick into the wall—if it comes out damp, keep waiting
- Good ventilation: Essential during drying. Keep windows open, use fans if available
Light straw-clay's porous structure allows moisture to escape from all surfaces simultaneously, unlike dense cob which dries slowly from outside to inside.
Thermal Properties
Light straw-clay is insulation, not thermal mass. It resists heat flow rather than storing heat. Your thermal mass comes from the earthen floor (already included in all designs) and the gabion stone foundation. For passive solar sites, consider adding an interior cob bench or feature wall if additional heat storage is desired.
Fire Resistance
Clay-coated straw is fire-resistant—the clay coating prevents the straw from igniting easily. In fire tests, light straw-clay chars on the surface but doesn't sustain flame. Combined with lime render, it provides excellent fire protection.
Repairs and Adjustments
One of light straw-clay's advantages is easy repair:
- Small gaps from settling: Stuff with more clay-coated straw
- Gaps at pole junctions: Pack additional straw around poles after they've finished shrinking (typically after first year)
- Cracks in render: Standard lime render repair (documented in Finishing section)
Unlike cob repairs which require matching the original mix and careful re-bonding, light straw-clay repairs are nearly invisible once rendered.
Chapter 6: Fire Safety & Native Restoration
Structure Fire Resistance
All BioDome designs have exceptional fire resistance due to their construction materials:
- Gabion stone foundation: Rock in wire mesh—completely non-combustible
- Light straw-clay walls: Clay-coated straw chars but doesn't sustain flame—the clay coating prevents ignition
- Living roof: Growing plants hold moisture. Soil and vegetation absorb heat without igniting
The only combustible elements are window/door frames and structural poles, but these are fully enclosed within the fire-resistant envelope. Fire would need to breach stone, clay-coated straw walls, and living roof before reaching any wood.
Optional: Stone Apron for Enhanced Fire Protection
In high-risk fire zones, consider adding a stone apron to the lower portion of walls. This creates a non-combustible barrier at ground level—where embers accumulate and ground fires make first contact.
Design
- Height: 50-100cm from foundation top
- Materials: Local stone (same granite used in gabions), dry-stacked or lime-mortared
- Thickness: 10-15cm facing, tied into wall with galvanized wire or stone anchors
- Upper wall: Standard lime render above stone apron
Construction Options
- Dry-stacked: Flat stones stacked without mortar, gravity-held. Allows wall to breathe fully. Easier to repair.
- Lime-mortared: Stones set in lime mortar (NOT cement—lime remains breathable). More permanent, better ember-sealing.
- Gabion extension: Continue the gabion cage upward 50-100cm before transitioning to straw-clay. Uses existing technique and materials.
Stone on the entire wall adds significant weight (stressing the eucalyptus frame), reduces breathability (risking moisture problems), and increases cost substantially. The lower 50-100cm addresses the highest-risk zone while preserving the benefits of light straw-clay above.
Native Forest Restoration: The Long-Term Fire Strategy
The most effective fire prevention is replacing eucalyptus with native forest. Eucalyptus is explosively flammable. Native Atlantic forests don't burn the same way.
Your BioDome project is part of this restoration. Every eucalyptus you harvest for construction is one less fire ladder. Every native tree you plant in its place is long-term fire insurance. Within 10-15 years, the replanted zone becomes a living firebreak.
Defensible Space Zones
| Zone | Distance | Treatment |
|---|---|---|
| Zone 1 | 0-5m | Zero flammable vegetation. Mineral surface only (gravel, stone, bare earth). |
| Zone 2 | 5-30m | Mowed grass, no eucalyptus, maintained fire breaks. Young native trees encouraged. |
| Zone 3 | 30-100m | Reduced fuel load, maintained access paths. Continue eucalyptus removal and native replanting. |
Focus on fire-resistant natives: Quercus robur (pedunculate oak), Quercus suber (cork oak), Castanea sativa (sweet chestnut), and Arbutus unedo (strawberry tree). These hold moisture, don't produce flammable oils, and create closed canopy that shades out eucalyptus regrowth.
Color-Coded Alert System
| Level | Conditions | Actions |
|---|---|---|
| GREEN | Wet season, recent rain, 60%+ humidity | Normal operations. Maintain defensible space routinely. |
| YELLOW | Dry spell, 40-60% humidity, no rain for 3+ weeks | No open flames. Wet defensible space weekly. Monitor weather. Keep evacuation kit ready. |
| ORANGE | High temps (>32°C), low humidity (<30%), fires reported in region | Wet structure daily. Prepare evacuation. Have vehicle fueled and exit route planned. |
| RED | Extreme danger, fires advancing, evacuation orders in effect | Evacuate immediately. Accept possible loss of structure. Life first, always. |
Part Two: Choose Your Design
Select the BioDome variant that matches your site and vision
Design Selection
All three designs share the same universal principles from Part One. What changes is the specific structural approach. Choose based on your site conditions, skills, and goals.
Standard BioDome
For open sites with no existing structures. Maximum thermal efficiency. Complex but elegant construction.
Terraced BioDome
For sites with terrace walls or existing stone structures. 40-50% fewer materials. Beginner-friendly.
Solar Pod
Off-grid energy independence. South-facing solar optimization. Complete electrical system guide.
Part Three: Design-Specific Construction
Choose your design and follow the construction details
Standard BioDome: Complete Design Details
Circular Design at a Glance
- Outer diameter: 10m (9m inner diameter wall)
- Floor area: 55m²
- Wall height: 3.5m to eaves
- Center height: 4.5m (at roof opening)
- Lifespan: 50+ years with maintenance (timber may need partial replacement at 30-40 years)
- Trees removed: 180-300 eucalyptus
Foundation: 10m Outer Diameter Circular Gabion Ring
- Outer diameter: 10m
- Ring width: 60cm (from outer to inner edge)
- Height: 50cm above grade, 30cm below
- Fill: Local granite, 10-25cm pieces
- Top surface: Level flat stones creating solid bearing for wall posts
Wall Framework
- Vertical posts: 24 main posts, 15-20cm diameter, 3.5m length, ~1.2m spacing
- Horizontal wattle: ~100 poles, 5-8cm diameter, 25-30cm vertical spacing, lashed to verticals
- Embedding depth: 40cm into gabion top
- Above-ground height: ~3.1m
Reciprocal Ring Beam
The ring beam uses the reciprocal principle—each pole rests on its neighbor and carries the next one in sequence. This dates to 12th century Buddhist temple construction (Todai-ji in Nara, Japan).
- Number of poles: 24 (matching wall posts below)
- Pole diameter: 12-15cm eucalyptus
- Span: Each pole spans approximately 2 post spacings
- Overlap: ~50cm where each pole rests on the previous one
- Fastening: 125mm galvanized spike at each overlap, plus wire lashing
- Stability: Even unbound, the geometry creates mutual support
Reciprocal Roof
- Main rafters: 12 poles, 15-18cm diameter, 5.5m length
- Purlins: Smaller poles (8-10cm) spanning between rafters
- Central opening: ~1m diameter for skylight/ventilation
- Roof angle: Controlled by the "rummy" (horizontal distance between connection points)
Ground Simulation First: Before raising beams, lay out the frame on the ground. Bring in each rafter and lay it across the last one about 50cm from its thinner end, building up the spiral flat. This reveals fit problems and lets you number poles for assembly sequence.
Living Roof
Sheathing
Cork board or dense wood fiber board over purlins
Waterproofing
EPDM pond liner (1mm minimum) fully lapped and sealed
Root Barrier
Drainage mat + filter fabric
Growing Medium
10-15cm lightweight substrate (pumice/perlite/compost mix)
Planting
Sedums, native succulents, drought-tolerant groundcovers
Terraced BioDome: Complete Design Details
Semicircular Design at a Glance
- Width: 9m (curved front face)
- Floor area: 24m² (half of standard)
- Wall height: 2.5m front wall
- Ridge height: 5.0m (where roof meets terrace wall)
- Cost: 40% cheaper than full BioDome
- Materials: 50-60% less than standard
Site Assessment: Evaluating Your Terrace Wall
- Structural integrity: No large displacement, bulging, or collapses
- Height: Minimum 2.8m (roof ridge will rest against or anchor into wall top)
- Length: At least 10m of usable wall
- Face condition: Reasonably flat or slightly curved (not severely convex)
- Base stability: No signs of tipping, settling unevenly, or undercutting
- Drainage: Water moves away from wall (you don't want a dam)
Foundation: 180° Semicircular Gabion Arc
- Shape: Semicircular arc (180°), radius ~4.5m
- Width: 0.6m (ring width from inner to outer face)
- Height: 0.5m above finished grade, 0.3m below (total 0.8m depth)
- Connections: Both ends tie into terrace wall base using steel plates or through-stones
Wall Framework
- Curved front posts: ~14 posts on semicircular front
- Wall-end posts: 2 additional posts where arc meets existing terrace wall
- Diameter: 15-20cm untapered
- Spacing: ~1.2m apart around the arc
- Horizontal wattle: ~7 levels × ~14 spans = ~98 pieces
- Wall thickness: 35-45cm light straw-clay (same method as standard)
Ring Beam and Lean-to Roof
The ring beam ties wall tops together. Both ends anchor into the terrace wall with threaded rods or steel plates.
Lean-to Roof Structure
- Rafters: ~14-15 pieces, 15-18cm diameter
- Spacing: ~1.2m apart (matching wall post spacing)
- Base (eaves): 3.0m height at curved front wall
- Ridge: 5.0m height at terrace wall (nearly at or slightly above wall top)
- Slope: 25-30° pitch (1:1.8 to 1:2.4 rise:run)
- Overhang: 1.0-1.5m beyond curved wall for weather protection
Purlins (Secondary Structure)
- Quantity: 3-4 purlins, 8-10cm diameter
- Arrangement: Semicircular arcs parallel to wall
- Attachment: Lashed and pegged to rafters
Living Roof
Roof Sheathing
Boards or rigid insulation over purlins (fast-draining to prevent pooling)
Waterproofing Layer
EPDM pond liner (1mm minimum), overlaps sealed
Root Barrier and Drainage
Landscape fabric + drainage mat for water movement
Growing Medium
10-15cm lightweight substrate (pumice/perlite/compost mix)
Planting and Establishment
Drought-tolerant sedums and native groundcovers
Solar Pod: Complete Design Details
Rectangular Off-Grid Design at a Glance
- Main floor: 5.0m W × 4.1m D = 18m²
- Sleeping loft: ~11m² (two compartments)
- Total living area: ~29m²
- Eaves height: 3.0m (front, south-facing)
- Ridge height: 5.35m (back wall, north-facing)
- Roof pitch: 30 degrees (optimal for solar in temperate climates)
- Solar array: 8 × 400W panels = 3.2kW
- Annual generation: ~4,200 kWh
Site Selection Requirements
- South-facing slope: Ideally 5-20 degrees natural slope
- Solar access: No shadows between 9am-3pm year-round (minimum 6 hours direct sun)
- Water source: Spring, well, or rainwater within 100m
- Level building platform: ~20m² relatively flat area
- Upper terrace: ~10m² elevated area for sleeping loft (can be partially dug)
- Drainage: Avoid low spots where water pools
Foundation: Rectangular Gabion
- Footprint: 5.0m × 4.1m rectangle
- Height: 50cm above grade, 30cm below grade
- Gabion mesh: Galvanized, 10×10cm openings, 3mm wire
- Fill: Local granite, 10-25cm pieces (hand-sorted)
Wall Framework and Light Straw-Clay Infill
- Vertical posts: ~16 posts total (6 front, 5 each side)
- Diameter: 15-20cm
- Horizontal wattle: ~80 poles, 5-8cm diameter, 25-35cm spacing
- Light straw-clay walls: 35-45cm thickness, same method as other designs
Roof Structure (Solar-Optimized)
Main Rafters
- Quantity: 5 parallel rafters
- Diameter: 15-18cm eucalyptus
- Length: ~4.7m along slope
- Span: From front eaves (3.0m) to back ridge (5.35m)
- Spacing: ~1.25m apart (east-west)
Purlins (Solar Mount Support)
- Quantity: 3 purlins running east-west
- Diameter: 10-12cm eucalyptus
- Length: 5.0m (full building width)
- Purpose: Support roof sheathing AND solar panel rail attachment points
Roof Weatherproofing (Critical for Off-Grid)
Roof Sheathing
Cork board or wood fiber insulation (30-50mm) creating R-1.2 insulation
Waterproof Membrane
1mm EPDM pond liner fully lapped (50+ year lifespan)
Drainage Mat
20-25mm HDPE dimpled mat (prevents pooling under panels)
If your roof leaks, everything fails. Spend time on the EPDM sealing. Use a sealer pen on all overlaps. Test with a hose before installing solar panels.
The Solar System
System Architecture (Sun to Light Switch)
- Sun hits 8 × 400W panels (3.2kW array) → DC electricity
- DC wiring (protected in UV-resistant conduit) → routes to inverter
- Hybrid inverter converts DC to AC (230V household voltage)
- AC wiring → powers lights, refrigerator, etc. OR charges battery
- Battery stores excess energy (5-10kWh LiFePO4)
- Backup generator kicks in if battery depletes
8 Solar Panels (400W Each)
- Dimensions: 2382mm × 1134mm × 30mm (about the size of a door)
- Weight: ~22kg each (manageable by 2 people)
- Type: Monocrystalline (20-22% efficiency)
- Configuration: 2 strings of 4 panels in series (parallel)
- Result: ~80V DC, ~25 amps (safe voltage for 48V hybrid inverter)
DC Wiring and Conduit Routing
- Panels on roof → junction boxes → UV-resistant conduit down slope
- Down north wall → into building to inverter location
- Wire sizing: 4mm² solar-rated cable (for 25-amp system)
- Grounding: Green/bare copper runs parallel (safety backup)
- Conduit clips: Every 2-3 feet securing to roof structure
Hybrid Inverter (3.2kW)
| Spec | Selection | Why |
|---|---|---|
| Power rating | 3.2kW or larger | Matches array capacity; higher avoids overload |
| Voltage | 48V DC input | Standard for this size; safer than lower voltages |
| Battery compatibility | LiFePO4 | Long life (10,000+ cycles), safer chemistry |
| MPPT controller | Built-in (essential) | Tracks panel performance, optimizes charging |
| Monitoring | WiFi-enabled app | Real-time view of power generation and usage |
Battery Storage (5-10kWh LiFePO4)
How much battery? 2-3 days autonomy = 6kWh daily load × 2 days ÷ 0.8 safe discharge = 15kWh needed. Budget for 5-10kWh initially, expandable.
- Chemistry: Lithium Iron Phosphate (10,000+ cycles, ~10-15 years)
- Efficiency: 96-98% round-trip
- Safety: More stable than other lithium chemistries
- Temperature: Works -10 to +55°C (heating required in cold)
Disconnects and Safety
| Disconnect | Location | Purpose |
|---|---|---|
| DC disconnect | Between panels and inverter | Cuts DC power (maintenance/safety) |
| AC disconnect | Between inverter and house loads | Cuts AC power to home |
| Battery disconnect | Between battery and inverter | Isolates battery for service |
| Generator disconnect | Between generator and system | Isolates backup generator |
Grounding (Earth Safety)
- Copper ground rod: 10ft long, driven into moist earth
- Grounding conductor: 4mm² copper from rod to main panel and inverter
- Metal conduit: Bonded (wired) to ground
- Testing: Measure resistance (should be under 25 ohms)
Professional Installation Required
| Task | DIY Risk | Recommendation |
|---|---|---|
| Plan the system | Low | Absolutely DIY—learn it |
| Install conduit on roof | Low | DIY with supervision |
| Panel interconnection | High (high voltage) | Hire certified installer |
| Inverter installation | High (DC+AC hazard) | Hire certified installer |
| Battery installation | Critical (fire/explosion) | Absolutely hire certified installer |
| AC wiring (house loads) | Medium-High | Hire licensed electrician |
Sleeping Loft (Vertical Space Strategy)
- Floor area: 2 × ~5.3m² compartments = ~11m² total
- Floor height: 3.0m above main floor (at upper terrace level)
- Ceiling height: 2.0m (tight but functional)
- Depth: 2.5m (extends into upper terrace)
- Width per compartment: ~2.1m
- Ladder access: One per compartment, ~60° angle from horizontal, 2.5m climb
Back Wall: Straw Bale Insulation (R-30)
The north-facing back wall uses compressed straw bales (450mm thick):
- R-value: R-30 (vs R-3.5 for fiberglass of same thickness)
- Fire resistance: Dense straw won't burn (clay plaster coating prevents flame spread)
- Breathability: Allows moisture to pass through
- Assembly: 1 bale high + 50mm lime plaster on both sides
Clerestory Window (5.0m × 2.3m)
- Location: Full-width north wall, where roof meets loft ceiling
- Purpose: Diffuse north light (no glare), stack-effect ventilation
- Design: Fixed panes with operable transoms (upper sections open)
- Summer control: External shade cloth or deciduous vine
Expected Daily Power Generation
- Sunny day: 12-15kWh generation, 6kWh use, 6-9kWh stored in battery
- Cloudy day: 3-5kWh generation, battery covers deficit
- Multi-day rain: Battery depletes; generator kicks in
- Winter months: Shorter days, lower sun angle; battery stores less
Realistic Daily Load (6kWh)
- Refrigerator: ~2.5kWh/day (non-negotiable)
- Lighting (LED): ~0.5kWh/day
- Water heating (solar thermal + backup): ~2kWh/day
- Internet/devices: ~0.3kWh/day
- Cooking (induction, sunny hours): ~1kWh/day
This works. But only if you're intentional about matching your use to the sun's availability.
Part Four: Finishing & Systems
Final details shared across all designs
Lime Render
- Base coat: 1:3 lime:sand, 15mm thick
- Finish coat: 1:2.5 lime:fine sand, 5mm thick
- Limewash: 3-4 coats for final protection
Windows & Doors
| Component | Standard | Terraced | Solar Pod |
|---|---|---|---|
| Main door | 1.0m × 2.1m | 1.0m × 2.1m | 1.0m × 2.1m |
| Side windows | 0.8m × 1.0m (×4) | 0.8m × 1.0m (×2) | 0.8m × 1.0m (×2) |
| Clerestory | Central skylight | Triangular N window | 5.0m × 2.3m N wall |
Use chestnut for frames (dimensional stability for weatherseals). Deep reveals (40cm+) create natural window seats.
Floor Options
- Earthen floor: Clay/sand/linseed finish (beautiful, requires maintenance)
- Flagstone on sand: Durable, attractive, low maintenance
- Polished concrete: Practical, can integrate radiant heating
Water System
- Rainwater harvesting: Living roof + gutters → storage tanks
- Storage: 10,000-15,000L recommended
- Treatment: First-flush diverter, filtration, UV sterilization
- Backup sources: Spring, well, or trucked delivery for dry periods
Power System
Standard/Terraced: Basic overview. Consider 2-4kW solar array + 10-20kWh battery if going off-grid.
Solar Pod: Refer to Tab C for complete electrical system guide.
Maintenance Schedule
Monthly Checks
- Inspect eucalyptus stumps for regrowth (first 18 months)
- Check roof drainage and clear debris
- Inspect lime render for cracks
- Monitor water system function
Seasonal Tasks
Spring (March-May)
- Full structural inspection
- Repair winter damage
- Plant natives in restoration areas
- Service any mechanical systems
Summer (June-August)
- Maximum fire vigilance
- Maintain defensible space weekly
- Water living roof if extended drought
- Monitor fire danger daily
Autumn (September-November)
- Apply limewash touch-ups
- Clean gutters and water system
- Prepare for wet season
- Assess restoration progress
Winter (December-February)
- Monitor for leaks
- Check drainage function
- Plan next year's improvements
- Document ecosystem recovery
Ecosystem Monitoring
Your BioDome is part of a larger restoration project. Document the recovery:
- Eucalyptus eradication: Stump survival rate by treatment method
- Native regeneration: Species appearing, coverage increasing
- Water recovery: Spring flow, well levels, soil moisture
- Biodiversity: Bird counts, insect diversity, mammal sightings
Your observations contribute to restoration science. Share with ICNF (Portuguese forest authority), Quercus (environmental NGO), or local universities.
Your Legacy
When you build a Regenerative BioDome—any of these three designs—you're not just creating shelter. You're:
- Removing 90-300 invasive trees from the landscape
- Returning thousands of liters of water daily to your watershed
- Eliminating major wildfire fuel from your land
- Creating habitat for native species recovery
- Demonstrating that restoration can be economically viable
- Building a home that will shelter your family for generations
With proper maintenance, the structure will serve you for 50+ years—the light straw-clay walls and stone foundation can last centuries. The native forest you enable will outlast all of us.
That's the real project.