The drawings show examples of construction solutions for wooden double-sided flat roofs with economical wooden roof girders. With a small slope of the roof, gravel mix can be used on the roofing.
The gravel should be rinsed and have a diameter of from 16 do 32 mm. The minimum layer thickness should be 5 cm. Ending the roof edges with internal drainage requires a special bumper inclined towards the center of the roof at an angle of at least 30 °, and the covering should protrude above the surface of the gravel cover at a minimum 10 cm and be attached to the outside of the fender surface. The supply and exhaust ventilation openings used so far have a net area of at least 2 ‰ (1/500) area of the entire roof slope, when damp materials were used for insulation.
The roof is divided on wooden girders made of boards (ending the roof on the edge with a wooden buffer): 1 – gravel sprinkles (pressure layer), 2 – three-layer roofing felt, 3 – full formwork for covering, 4 – wooden girder made of boards, 5 – thermal insulation, 6 – longitudinal strips for attaching the soffit, 7 – roof lining made of plasterboards, 8 – air inlet holes, 9 – ventilated airspace, 10 – wooden buffer, 11 – air flow direction, 12 – vapor barrier
Cross-section through a wooden flat roof on lattice girders made of boards and with a soffit made of plasterboards. Designations as in fig. higher
Light, wooden double-sided flat roof on glued I-beam girders (cross-sections for two solutions of coverage): 1 – an I-girder with a plywood or hard fibreboard web, 2 – three-layer roofing felt, 3 – gravel sprinkles, 4 – waterproof layer made of PVC foil, 5 – leveling and separating layer made of polyethylene foil, 6 – full formwork for covering, 7 – thermal insulation, 8 – vapor barrier, 9 – plank roof lining, 10 – plaster on a plaster grid, 11 – ventilated air space
In fig. on its left side, on the upper surface of the roofing felt, there is a special sprinkle reflecting thermal radiation. On the right, under the gravel layer, there is a waterproof layer made of PVC foil. The remaining layers of the flat roof under the waterproof layer are the same in both alternatives