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.
Shingles need a continuous deck and a starter course laid upside down at the eaves so that the cut-outs of the first visible course are backed by solid material. They are nailed high enough on the strip that the next course covers the nail heads. Ridge pieces are cut from the same material and lapped against the prevailing wind.
Profiled sheet is fixed through the crown of the profile, not the trough, so that the fixing sits above the water line and the washer compresses onto a flat surface. Sheets are laid with the side lap away from the prevailing wind. Whatever the covering, the same rule applies: fixings go where water is not, and laps face the way water is going.
150 mm lap at every course
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