Leak risk starts with the choice of covering. Matching it to the pitch, correct laps and tight details around openings and edges are essential. The layer beneath the covering must drain water away from the building. Each system has its own conditions of use – check the documentation for the specific profile, thickness and roof layout, as the T18 or T35 label does not set a single minimum for all products. Accept the roof in stages, because some faults become invisible after the sheets are fitted and the attic is finished. Agree the design of the details with the designer.

After noticing a roof leak, first limit damage inside the building and ensure safety rather than immediately searching for the source above the stain. Water can travel along roof components, so the wet patch need not lie beneath the leak. Check whether the problem occurs during ordinary rain, strong wind or a thaw, and whether the stain grows gradually or appears suddenly. Recording these conditions helps choose places to inspect without unnecessary dismantling. Leave the diagnosis of causes and the scope of repair to a contractor, who should describe the defect found.

The underlay membrane beneath metal roofing is there to intercept water that gets under the covering and direct it outside before it reaches the insulation or structure. When choosing, check whether the manufacturer allows installation on the given substrate, along with water resistance, temperature range and the durability of joints. The Sd value alone does not settle suitability, because the whole roof assembly matters. Also establish how laps and the eaves termination are detailed, since these determine how the membrane performs in practice.

A good roofer inspects the roof and asks questions before giving any quote. They take an interest in the roof's construction, its dimensions and whether the details match the covering documentation. Photos of completed jobs help, but they do not replace a clear offer. Watch how the contractor responds to uncertainties and suggested changes. For a renovation, they should enquire about earlier leaks and whether the loft can be accessed. A quick price is only a preliminary estimate, not a full diagnosis — so they should state plainly what they have not yet checked and what might alter the scope.

Start by putting the offers into a single table, because comparing prices per metre alone usually says nothing about the scope of work. Establish who is responsible for measurements and for accepting details that will disappear under the covering, and ask for a quote based on the same materials and accessories. For a renovation, add attic photos and information about leaks — an estimate from the elevation alone is preliminary. Choose a team that knows the given system, not merely one experienced in laying roof tiles.