Why build from timber at all?

A plastic dalek bin is cheap and keeps the rain off, but it has one serious flaw: it holds water and shuts out air. Composting is an aerobic process, and the bacteria and fungi doing the work need oxygen. Without it you get a slimy, smelly, slow heap rather than a hot, crumbly one. A timber bay with deliberate gaps between the boards gives you airflow from the sides, and a removable front means you can fork the whole heap out and back in again in twenty minutes. Reclaimed timber makes it cheap, too. A single bay built from scrap decking boards and a couple of fence posts will cost you very little and will outlast most plastic bins left in full sun.

Choosing a spot and a size

Pick level ground. A sloping site lets the base rot unevenly and makes the bin awkward to load. Sit it on paving slabs, a couple of concrete blocks, or a square of old scaffold board — this stops couch grass creeping up into the heap and keeps the bottom slats off wet soil.

Put it somewhere you don't mind walking to in February with a full bucket, ideally beside a hard path so you're not tramping mud into the kitchen. Part shade is fine; full sun dries a heap out faster than you'd think.

For size, aim for a bay around 1m x 1m x 1m. Below about 75cm cubed, a heap loses heat faster than it generates it. A three-bay system — one filling, one cooking, one finishing — is the classic allotment set-up, but start with one bay and add a second when you find you need it.

Sourcing and preparing reclaimed timber

Good sources include old fence panels, scaffold boards, pallet wood (the thick bearers are the useful bits), decking offcuts and broken shed boards.

• Avoid anything creosoted, painted with old lead paint or soaked in engine oil. Skip MDF, chipboard and plywood as well — they collapse outdoors within a season.
• With pallets, look for the HT stamp, meaning heat treated. Avoid MB, which means methyl bromide.
• Modern tanalised timber is fine for a compost bin and will last years longer than untreated scrap.

Sort your timber into two piles: sturdy pieces for the corner posts (75mm x 75mm or thicker) and thinner boards for the slats. Cut everything to length on a dry day and pull out old nails with a claw hammer or wrecking bar before you start — a nail through the thumb ruins the afternoon.

Assembling the frame and slats

Set four corner posts into shallow holes, or simply sit them on the slabs and brace them upright with a spirit level. Fix the back and the two sides first, leaving the front open.

Screw or nail the slats to the outside of the posts so the inside face stays smooth and nothing catches when you fork the heap out. Space the boards with a 25–40mm gap. A scrap of batten makes a handy spacer — drop it between each board as you fix the next one. You can close the gaps on the bottom third if you like, but leave the upper two-thirds open to the air.

Use galvanised screws or nails. They cost a little more and save you rebuilding the thing in three years, which untreated fixings in damp timber will absolutely require.

Building a front you can lift out

This is the bit that makes the bin worth having. Three workable approaches:

• Slat and slot: fix two short vertical battens on the inside of the front posts to form a channel, then drop the front slats down into it. Lift them out one at a time as you work down the heap.
• Removable centre post: run a post up the middle of the front, secured top and bottom with a single coach bolt each, and slot short boards either side of it. Undo the bolts and the whole face comes away.
• Hinged panel: the tidiest option, but you'll need decent galvanised hinges — cheap ones rust solid within a year.

Whichever you choose, the front slats should sit tight enough to hold the heap in. Test it with a full bay of grass cuttings before you congratulate yourself.

Filling, turning and keeping it working

Aim for roughly two parts browns to one part greens by volume. Browns are cardboard, torn paper, straw, dead leaves, woodchip and spent compost. Greens are grass clippings, kitchen peelings, coffee grounds, annual weeds and plant trimmings.

Turn the heap when it starts to cool, or every three or four weeks through summer. Fork it out into the next bay, or onto a tarpaulin if you only have one, mixing as you go. That single act is what separates a bin that works from a bin that sulks.

Keep it as damp as a wrung-out sponge — watering in dry spells and covering with an old piece of carpet or a tarpaulin during torrential rain. A well-built bay will hit 60–70°C in the middle within a week or two, and you'll see steam rising when you turn it on a cold morning. That's the sign you've got it right.