Building a compost bin from recycled timber is one of the most satisfying weekend projects a NZ homeowner can tackle. It costs very little, keeps usable wood out of landfill, and gives you a steady supply of rich compost for your garden. With basic tools and a free afternoon, you can have a sturdy, functional bin ready to fill.
What You'll Need
Before you start, gather your materials and tools. Recycled timber is ideal — old fence palings, pallet timber, or rough-sawn offcuts all work well. Avoid timber that has been treated with older preservatives (such as CCA, which contains arsenic and chromium), as leachate from these can contaminate your compost and soil. If you're unsure about the treatment type, check with your timber supplier or err on the side of caution and source different wood. WorkSafe NZ has guidance on handling treated timber safely.
Materials:
- Recycled timber boards or fence palings (rough-sawn is fine)
- Four corner posts, approximately 75 x 75 mm and 900 mm long
- Galvanised screws or nails (stainless steel is even better for longevity)
- Optional: galvanised wire mesh or shade cloth for the base
Tools:
- Tape measure and pencil
- Hand saw or circular saw
- Drill/driver
- Spade or post driver
- Safety glasses and gloves
Choosing the Right Location
Pick a level, well-drained spot that gets partial sun — full shade slows decomposition, and full sun dries the pile out too quickly. NZ's variable climate means a sheltered spot (out of prevailing winds) helps maintain moisture. Keep the bin at least 500 mm from your boundary fence to allow access and airflow, and check your local council's rules, as some have guidelines around composting near boundaries or waterways.
Sizing Your Bin
A good working size for a home compost bin is 1 metre wide × 1 metre deep × 1 metre tall. This is large enough to generate the heat needed for effective composting, but manageable for turning. If you have a large garden, consider building two or three bays side by side so you can turn material from one bay to the next.
Step-by-Step Construction
Step 1 – Prepare Your Corner Posts
Cut four corner posts to approximately 900 mm. Drive or dig them into the ground at least 300 mm deep, forming a square roughly 1 metre on each side. Check they're reasonably plumb using a spirit level.
Step 2 – Attach the Side Boards
Cut your recycled boards to length and screw or nail them horizontally to the inside face of the corner posts, working your way up from ground level. Leave a small gap (around 20–30 mm) between each board to allow airflow — good aeration is essential for fast, healthy composting.
Step 3 – Leave the Front Open or Removable
For easy access when turning or removing finished compost, leave the front open or make it removable. A simple method is to slot boards loosely between two front posts with small timber cleats screwed to the posts as guides. This lets you slide boards in and out as the pile grows or shrinks.
Step 4 – Sort Out the Base
You don't need a solid floor — in fact, direct contact with soil encourages worms and beneficial microbes to enter the pile. If you're worried about rodents, staple a layer of galvanised wire mesh (13 mm aperture) across the base before positioning the bin.
Step 5 – Finishing Touches
A loose lid (a piece of old carpet, a sheet of corrugated iron, or a timber frame covered in shade cloth) helps retain moisture and warmth. It also keeps heavy NZ rain from waterlogging the pile.
What to Put In (and What to Leave Out)
| Add (Greens & Browns) | Avoid |
|---|---|
| Grass clippings, vegetable scraps | Meat, fish, dairy |
| Fallen leaves, cardboard | Diseased plant material |
| Coffee grounds, tea bags | Treated or painted timber |
| Garden prunings (chopped small) | Pet waste |
| Straw, paper | Invasive weeds with seeds |
Aim for a roughly equal mix of 'greens' (nitrogen-rich, wet material) and 'browns' (carbon-rich, dry material). Turn the pile every few weeks to speed things up. BRANZ and Energywise both highlight composting as a practical way to reduce household waste and improve soil health.
Timber Longevity Tips
Untreated recycled timber will eventually rot — that's the nature of the beast. To extend its life, keep the timber off the ground where possible, and consider painting the exterior faces with a water-based exterior paint or timber oil. Resene and Dulux both offer suitable exterior timber coatings. Avoid painting the interior faces that will contact compost.
Does This Need a Building Consent?
In most cases, a simple garden compost bin does not require a building consent under the NZ Building Code — it's a small, non-habitable garden structure. However, rules can vary by council and site. Always confirm with your local council before building, particularly if you're in a heritage zone or have specific site conditions. MBIE Building Performance has useful guidance on Schedule 1 exemptions.
When to Call a Professional
Building a compost bin is well within most homeowners' DIY abilities and doesn't involve any restricted trade work. However, if your project grows into something more ambitious — like a large retaining wall to create a composting area, or landscaping that involves significant earthworks — it's worth getting a qualified landscaper involved. A professional can also advise on soil health, drainage, and garden design. You can find experienced local landscapers on tradedirectory.co.nz.
Licensed Building Practitioner (LBP)
