Little Wood Buildings
Notes on small timber buildings: how they are framed, clad, roofed and kept dry.
Scale models of vernacular buildings
Building a small structure at model scale is a useful way to understand one at full size. The sequence is identical: a base, a floor frame, wall panels, a roof. Only the material thicknesses change, and a chosen scale makes them change consistently rather than by guesswork.
A declared scale is what makes the exercise worth anything. At one to twenty-four, a millimetre on the model stands for twenty-four at full size, so a nominal board can be worked out rather than estimated. Keeping a scale rule or a written conversion on the bench stops the roof drifting into a different scale from the walls, which is the most common way a model stops reading as a building.
Insulating a garden workroom
A workroom that is used in winter needs insulation, and insulation changes the way the wall handles moisture. A cold uninsulated shed is wet and dries out; an insulated one has a warm side and a cold side, and water vapour from the warm side will condense when it reaches a surface cold enough. The build-up has to account for that or it will quietly rot.
Working from the outside in, the order is cladding, a ventilated batten cavity, a breather membrane, the insulated stud zone, a vapour control layer, and then the internal lining. The breather membrane keeps liquid water out while letting vapour escape outwards. The vapour control layer on the warm side limits how much vapour gets into the construction in the first place.
Firewood does not dry in a sealed box; it dries in a draught with a roof over it.
Treating and painting softwood
Softwood used outdoors is either pressure treated at the mill or coated on site, and most small buildings are both. Pressure treatment protects the timber that was in the tank; it does not protect the face a saw has just exposed. Cutting a treated board leaves untreated end grain, and end grain absorbs many times more water than a face does.
The practical consequence is that cut ends are coated with an end grain preservative as they are cut, on the bench, before the piece goes into the building. Once the board is fixed, the end that mattered most is usually the one buried against a corner post or sitting on a sill where no brush will ever reach.
Windows in a small building
Every opening is a deliberate weakness in the wall, so the number and size of windows is worth deciding on use rather than on appearance. A workroom wants light on the bench. A store wants none at all, and a store with no window has one less detail to keep watertight and one less invitation to anyone passing.
The sill is the detail that decides whether the opening survives. It slopes away from the frame so water runs off rather than sitting on the joint, it projects past the cladding face, and it has a groove on its underside so that water running back along the soffit drops clear instead of tracking to the wall. A flat sill with no projection and no groove will wet the wall below it at every shower.
Point the brace up from the hinge, and gravity works for the door instead of against it.
Felt, shingle and sheet roofs
Three coverings account for most small timber buildings. Mineral felt is cheap, quick and forgiving on shallow pitches. Bitumen shingles cost more, look domestic and want a steeper pitch. Profiled sheet, whether metal or bitumen fibre, spans between purlins and can go on without a full deck underneath.
Felt is laid in courses from the eaves upwards so that each course laps over the one below. The laps run across the fall, never with it, and the covering is turned down over the eaves edge and fixed under a batten so the wind cannot get beneath it. Most felt roofs that fail have failed at an edge or a lap rather than in the middle of a sheet.
Shiplap and featheredge cladding
Shiplap and featheredge do the same job by different means. Shiplap is machined with a rebate so that each board locks over the one below and presents a flat face. Featheredge is a plain tapered board, thick at the bottom edge and thin at the top, laid so that each board overlaps the one beneath. Both shed water downwards and outwards; neither is watertight on its own.
Because boards move across their width with the seasons, each one is fixed with a single line of fasteners rather than pinned at both edges. A board nailed top and bottom cannot expand, so it splits instead. Fixings are kept back from the board ends by a comfortable margin for the same reason, and pre-drilling near an end is worth the extra minute.
The overhang is not decoration; it is the cheapest weatherproofing on the building.
Stud walls for a garden store
Wall panels for a small building are framed flat on the finished deck and then stood up. Working flat means every joint can be squared and fixed without holding anything in the air, and the deck itself acts as the reference surface. Each panel gets a sole plate at the bottom, a head plate at the top and studs between them at regular centres.
Stud centres are set by what the cladding and any lining will land on, not by habit. Openings are framed by doubling the studs on each side and adding a header across the top, so that the load from the roof travels around the opening rather than over unsupported timber. A sill piece at the bottom of a window opening gives the frame somewhere to sit and keeps the opening from racking.
Timber floor frame on bearers
The floor frame carries the building and sets its geometry, so it is worth more care than anything above it. Two bearers run across the slabs, the joist frame sits on the bearers, and the deck goes on last. Because the bearers run the short way and the joists the long way, the load path from the deck down to the ground is short and obvious.
Squaring the frame is done by diagonal, not by eye. With the perimeter joists nailed together, the two corner-to-corner measurements are compared and one corner is pushed until they match. Only then is the frame fixed off and the intermediate joists dropped in. If the frame is out of square here, every wall panel, every door and every sheet of cladding above it will be fighting that error.
Everything a small building does wrong later, it usually learned on the first morning, from the ground.
Filed under
Notes dated 11 March 2024 to 12 June 2025