18/08/2026
Composting Toilet – Materials & Build Guide
This is based on the timber toilet design above. I’d build it approximately 1.2 m wide × 1.6 m deep, with an internal floor raised about 450–600 mm above ground level to create space for the composting container/chamber beneath.
For a hot, wet climate, the important features are good ventilation, large roof overhangs, keeping rainwater away from the chamber, termite protection and easy access for emptying.
Approximate Finished Size
Footprint: 1.2 m × 1.6 m
Front wall height: approximately 2.5 m
Rear wall height: approximately 2.1 m
Raised toilet floor: 450–600 mm
Door: approximately 700 × 1,900 mm
Roof: approximately 1.7 × 2.1 m including overhang
Compost access hatch: approximately 500 × 500 mm
Vent pipe: 100 mm PVC
External sink shelf: approximately 900 × 450 mm
Materials
Foundations and Base
6–8 concrete blocks or small concrete footings
Cement
Sand
Aggregate
Damp-proof membrane or roofing membrane
Galvanised anchor bolts/brackets
Gravel for drainage around the building
A full concrete slab isn't essential. I would probably use individual concrete pads so the timber structure sits above the wet ground.
Timber Frame
Use treated structural timber.
Approximately:
50 × 100 mm timber — 35–40 metres
50 × 50 mm timber — 20–25 metres
25 × 100 mm timber for battens/trim — 20 metres
Exterior timber cladding — approximately 18–20 m²
Floor boards or 18–20 mm exterior plywood — approximately 3 m²
Exterior plywood for toilet platform — approximately 1 sheet
In Thailand I'd make termite treatment a priority before assembling it.
Roof
Corrugated metal roofing — approximately 4 m²
Roofing screws with rubber washers
Timber roof battens
Flashing
Drip edge
Optional gutter
Optional small rainwater tank
I'd use metal rather than transparent plastic sheeting because the toilet will be considerably cooler.
Door
Timber boards
50 × 75 mm framing timber
3 heavy-duty black hinges
Handle
Latch
Internal bolt
Door stop
The diagonal timber brace can give it the barn-door appearance shown in the picture.
Ventilation
100 mm PVC pipe — approximately 3 metres
100 mm PVC elbow
Pipe brackets
Roof/weather cap
Fine insect mesh
Optional 12 V extractor fan
The pipe should start in the compost chamber and finish above the roof line.
A small solar-powered fan would make the system much better in hot weather.
Composting Toilet Components
I would not build one huge permanent pile underneath the toilet.
For a small homestead toilet, removable containers are much easier to manage.
Use:
Composting toilet seat or normal toilet seat
Timber toilet box/platform
40–60 litre heavy-duty containers with lids
At least 3 containers so they can be rotated
Urine-diverting toilet insert if possible
Urine hose
20–30 litre urine container OR drainage to an appropriate treatment system
Sawdust/rice husk/coconut coir storage container
Small scoop
Rubber seals around access hatch
A urine-diverting toilet will smell considerably less and makes the solids easier to compost.
External Hand-Washing Station
900 × 450 mm timber worktop
Basin
Tap
20–50 litre clean-water container or connection to water supply
Waste pipe
Soap dispenser
Small mirror
Timber shelf brackets
Run the greywater into a gravel/plant filtration area rather than underneath the toilet structure.
Windows and Ventilation
I'd have:
One high opening window
One louvred vent on the opposite wall
Insect mesh over both
Small gap beneath the roof if protected from rain
Cross-ventilation will make a very large difference.
How to Build It
1. Mark Out the Site
Mark a rectangle approximately:
1.2 m × 1.6 m
Choose slightly elevated ground if possible.
Remove vegetation and approximately 100 mm of topsoil.
Put gravel beneath and around the structure so rain doesn't leave the timber sitting in wet soil.
2. Make the Footings
Install concrete pads beneath each corner and underneath the main structural members.
Set galvanised post bases or anchor brackets into the concrete.
The timber itself should ideally never touch the soil.
You could raise the entire building another 100–150 mm above ground level.
3. Build the Bottom Frame
Make a rectangular timber frame from 50 × 100 mm timber.
Add cross-members approximately every 400 mm.
This forms the structural base of the toilet.
Check everything is square by measuring diagonally corner-to-corner.
4. Create the Compost Chamber
The rear or side section underneath the toilet becomes the service area.
Allow approximately:
600 × 600 × 500 mm
or larger.
Fit a removable collection container underneath the toilet.
Leave enough room to slide the container completely out through the external hatch.
This is important — don't make the hatch just big enough to look right. Make it big enough to actually work comfortably.
5. Build the Raised Floor
Install joists and floor boards approximately 450–600 mm above the bottom frame.
This leaves space underneath for the compost system.
Cut an opening where the toilet pedestal will sit.
Waterproof or seal the timber immediately around the toilet.
6. Build the Wall Frames
Construct the four wall frames on the ground.
Use approximately 50 × 100 mm timber.
Stud centres can be around 400–600 mm.
Make the front wall taller than the rear wall to create the roof slope.
Frame openings for:
Door
Window
Vent
Compost access hatch
Sink plumbing
Stand each wall up and screw/bolt them together.
Brace everything before installing cladding.
7. Build the Roof
Run rafters from the high side toward the low side.
Allow generous overhangs:
300–450 mm minimum.
I'd make the overhang above the door closer to 500–600 mm.
Fit roof battens followed by the corrugated metal sheets.
Use screws with rubber sealing washers.
The roof should slope sufficiently that tropical rain disappears quickly rather than sitting on it.
8. Install the Exterior Cladding
Fix vertical timber boards to the frame.
Leave sufficient expansion gaps.
Seal the timber with an exterior wood treatment.
A natural oil finish would give you the same sort of appearance as the design.
Make sure the bottom edge of the cladding remains clear of soil.
9. Build the Door
Build a simple framed timber door.
Add the diagonal brace.
Fit three hinges because solid timber doors become surprisingly heavy.
Install the latch and an internal bolt.
Leave ventilation clearance without making openings large enough for insects or rodents.
10. Build the Compost Access Door
Make the hatch approximately 500 × 500 mm or larger.
Fit:
Two or three hinges
Latch
Rubber/weather seal
The hatch needs to keep rain, insects and rodents out.
The collection container should slide directly toward the opening.
11. Build the Toilet Pedestal
Make a timber box approximately:
450 mm high × 450 mm wide × 600 mm deep.
Fit a conventional toilet seat on top.
Inside, position the solids container directly beneath the opening.
If using urine separation, mount the urine-diverting insert at the front and run a hose downward.
Make the front or top of the toilet box removable so it can be cleaned.
12. Install the Vent Pipe
Run 100 mm PVC from the compost chamber vertically upwards.
Avoid unnecessary horizontal sections.
Take it above the roof.
Fit:
Insect mesh
Rain cap
Optional extractor fan
The vent works best when the upper pipe receives sunlight because warming the pipe improves the chimney effect.
Painting the upper section black can increase passive draught, although in the tropical sun a fan probably gives more predictable ventilation.
13. Install the Window and Louvres
Put a window high on one wall.
Put another louvred opening on the opposite side.
This produces crossflow through the toilet room.
Cover openings with mosquito mesh.
14. Build the Outside Sink
Fix two substantial timber brackets to the wall.
Install the timber counter.
Drop or sit the basin into it.
Fit a simple tap.
Water can come from:
Mains water
Elevated tank
Rainwater tank
Run the wastewater to a gravel-filled soakaway or planted greywater area.
Do not run sink water into the compost solids container.
15. Protect the Timber
Treat all exposed timber against:
Termites
Fungal decay
UV
Moisture
Pay particular attention to the bottom 300 mm of the building.
I'd also leave a gravel strip approximately 300–500 mm wide around the whole toilet rather than allowing plants and soil directly against the timber.
16. Start the Toilet
Put approximately 50–100 mm of dry carbon material into the bottom of the solids container.
Suitable materials include:
Sawdust
Rice husks
Chopped dry leaves
Coconut coir
After solid use, add a small handful of dry material.
The aim is moist, not wet.
Urine separation makes this dramatically easier.
17. Rotating the Containers
When one container is approaching full:
Close it with its lid.
Replace it with an empty container.
Transfer the full container to a secure compost maturation area.
Allow adequate composting/maturation time before considering any end use.
For edible crops, I would be conservative: don't use partially treated human waste directly around vegetables. Follow local sanitation requirements and use a properly managed, contained composting process.
One Change I'd Make to the Picture
I would actually make the toilet building slightly wider than the illustration.
Something around 1.4 × 1.7 m would cost very little extra but give enough room inside for:
toilet + dry material bin + toilet roll + small shelf + cleaning equipment without feeling cramped.
And because you're already planning chickens, vegetables, fruit and fish tanks, I'd put this toilet near the growing area but on the outer edge of the site, rather than right next to either the chicken house or fish tanks.
That would make it feel like a deliberate part of the whole Off Grid Life setup rather than just an outside toilet.
