The covering decides how a rooflight is flashed into the slope. Concrete tiles, clay tiles and slate each need their own flashing kit, and an older roof may have been patched with mixed materials that need to be understood before a hole is cut.
We look from the ground, then from the loft and, where it is safe, from the roof itself. We check the battens, the rafters and the felt, and we note any sag that would stop a new frame sitting square.
Where a roof faces a street and the house sits in a conservation area, the choice changes. A low-profile unit that lies flush with the covering keeps the roofline changing as little as possible, and the slimmer frame suits older stock.
Pitch changes the choice of unit. A low pitch limits how far a roof window can open and how much glass is visible from below, while a steep pitch gives a more upright view and more usable light. Both are workable, and we match the frame size to the rafter spacing so as little timber as possible is cut. Any rafter that is cut gets a new header and doubled timbers either side, so the loads travel round the opening.
Flashing is where a roof can fail, so we treat the junction as the main task and not as an afterthought. Each kit is made for the covering it meets, and lead or aluminium soakers are lapped so water runs away from the frame in every direction.