A roofing membrane is a layer under the covering that protects against water and allows water vapour to escape. When selecting its parameters, check above all the product's intended use, diffusion resistance Sd, waterproofness and mechanical strength. Grammage alone is not enough for assessment. The key decision variable is compatibility with the temperature under the covering, the type of substrate and the planned installation time. Remember that the membrane does not replace the metal sheet or the internal airtight layer, and its strips and joints must form a continuous layer.

Limiting the risk of leaks depends above all on the pitch chosen for the specific roofing material, not on the thickness of the sheet metal alone. Check whether the slope on the actual structure meets the product's requirements, especially where the length of joints or the presence of openings changes the conditions of use. Plan the laps, supports and details at the chimney, valley or window before ordering. Remember that in roof panels a continuous panel differs from a system with a transverse lap. Inspect the installation in stages, before the layers are covered.

After noticing a leak, limit the damage inside and have the cause determined. The position of the stain on the ceiling need not lie directly beneath the damaged covering. Water can travel through the roof layers. Condensation can produce a similar symptom. Do not go onto a wet roof slope in search of a hole. An effective repair begins with a safe inspection and with distinguishing the source of the moisture. Move objects away from the drip point and restrict access to the affected part of the room. If water is near electrical installations, an assessment and safe handling by a competent person are required. Do not touch wet equipment. A sagging ceiling lining or plaster coming loose may pose an additional hazard to people beneath it.