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Why a lean-to beats a freestanding store

A lean-to log store tucked against the side of a shed is one of the most useful structures you can add to a garden. It costs very little in materials, it takes up ground that was doing nothing anyway, and it keeps your firewood genuinely dry rather than merely covered. The shed already provides one wall, a firm base and something to fix a roof to, so you are effectively building two sides and a lid instead of a whole building.

The trick is to treat it as a proper structure rather than an afterthought. Get the base, the airflow and the roof pitch right and the wood will season well and burn hot. Get them wrong and you will be stacking damp logs that smoke, spit and clog the flue.

Choose the position before you buy anything

Face the open front towards the sun and, if you can manage it, away from the prevailing wind. In most of the UK that means a south or south-west aspect, with the closed back against the shed. Sun on the front of the stack drives moisture out; driving rain on the front puts it back in.

Think about access too. You want to walk up to the store with a wheelbarrow or a log basket without squeezing past a greenhouse or a water butt, so leave at least a metre of clear standing room in front.

On the legal side, a lean-to under 2.5 metres to the eaves is normally permitted development, but check the rules if you are in a conservation area, a listed building or a property with restrictions on the title. It is a five-minute check that saves a great deal of trouble.

Set out the footprint and leave a gap

A practical depth is 600–750mm. That takes two rows of logs split to around 250–300mm, which is enough capacity to be useful without making the back of the stack unreachable. Widths of 1.8m or 2.4m suit standard sheet roofing and are easy to build in bays.

Height should fall from the shed to the front. Aim for roughly 2.1m at the back and 1.8m at the front, which gives you a roof fall of about 1 in 40 — comfortably more than the 1 in 80 minimum you need for most sheet materials.

Critically, leave a 25–50mm gap between the back of the store and the shed wall. It feels counterintuitive to build a gap into something designed to keep rain out, but that slot is what stops damp air sitting against the shed cladding and rotting the panels. It also lets you inspect the wall occasionally.

Raise the logs off the ground

Ground contact is what turns firewood into compost. Timber sitting on soil or concrete will wick moisture upward and grow mould within a season.

• Excavate 100mm, compact the sub-base, then lay concrete paving slabs or a strip of well-compacted gravel.
• Sit 50mm tanalised bearers on top of the slabs, running front to back so air can move along them.
• Lay a slatted timber floor across the bearers, or simply use pallets if you want a quick and effective solution.
• Keep the finished floor level at least 100mm above the surrounding ground, and higher if the site is boggy.

The aim is a floor you can see through. If air cannot get underneath the bottom row of logs, that row will be the first to go soft.

Build the frame, then cover it properly

For a lean-to of this size, a simple frame of 75mm x 75mm tanalised posts at the front with a ledger fixed to the shed is ample. Fix the ledger into the shed's frame rather than just its cladding — coach screws into the studs will hold far better than screws into feather-edge boards.

Run rafters from the ledger down to a front beam, spaced at 600mm centres, and set them so the roof falls away from the shed. Cover with corrugated bitumen sheet, box-profile metal, or EPDM on a ply deck. Corrugated sheet is cheap, light and easy to cut, and it lasts decades.

Flash the junction where the roof meets the shed wall with a lead or butyl apron dressed up under the cladding. This is the one detail people skip, and it is the one that causes damp patches inside the shed.

Keep the air moving and the rain out

Logs dry by airflow, not by heat. That means three sides should breathe. Build the side panels as slats with 20–30mm gaps, or leave one side entirely open if the weather allows. Never clad the store in solid boarding and hope for the best.

Divide the store into two bays if you can. Fill one with this year's wood and draw from the other, so you always have a seasoned stack and a seasoning stack. Hardwood generally needs twelve months, softwood around six, and you are looking for a moisture content below 20 per cent before it goes on the stove.

Finally, keep an eye on the details that fail first: the bearers at the base, the flashing at the top, and any fixings left exposed to the weather. Ten minutes with a screwdriver and a tin of wood preserver each autumn will keep the whole thing sound for years.