Rooflights and skylights in Leatherhead, beside the Mole

Leatherhead sits on the River Mole in Surrey, about 17 miles south of central London and 22.7 road miles from Crawley, comfortably inside the thirty miles we cover.

The name most likely comes from a ford, a place where the river could be crossed, and the town grew along the water from there. At the 2011 census the town itself held 11,316 people, and the built-up area running out towards Effingham held 32,522. So Leatherhead is a real town with a real edge, and then a long tail of housing that blends into the next place along.

The planning authority is Mole Valley District Council, with Surrey County Council above it. That matters more than it sounds, because the council that judges a roof window on a Leatherhead terrace is also the council that wrote the town's conservation area guidance. One set of officers and one set of documents apply, and we read them for your address before we talk about products.

Early twentieth-century housing grew around Fairfield, Highlands and Kingston Roads, and those streets are where a rooflight conversation in this town often begins. The roofs in them were framed a century ago, and what is in the loft is the first thing to establish.

Council housing began in Leatherhead in 1921, and there was post-war rebuilding after bomb damage. So the town holds homes from at least three separate building waves: the early twentieth-century streets, the council estates that started just after the First World War, and the replacement housing put up once the damage was cleared. We do not assume which one you live in. The loft hatch tells us.

What we look for is how the roof was framed. Hand-cut rafters can usually take a new opening framed between them with trimmers, and a roof window can be set in line with the covering. Factory trusses carry load through every member, and cutting one casually is a mistake that shows up as a sagging ridge months later. Where trusses are present, the structure around the opening is supported first, and the survey says so plainly. That is a question for someone standing in the roof space with a torch, not for a catalogue.

Most of the choice comes down to which room the light is going into and what that room hears. A table is the quickest way to set it out.

A rooflight on a flat extension roof meets rain differently from one on a slope, and the drumming is easy to underrate until the first downpour.

A flat roof is never dead level. It is laid to a fall, commonly 1:80, so that water runs to an outlet instead of standing. A kerb for a rooflight sits on that surface and has to be built to suit it. If the fall is poor, water collects at the upstream edge of the kerb, and the glazing sits in it. That is a problem for the roof, not the glass, and it is why the survey looks at the roof first.

Rain noise is a separate matter. Raindrops hitting a thin pane are loud, and the same drops on laminated glass with a heavier inner pane are far quieter. A thicker outer sheet, a deeper kerb and a suitable lining can all soften it. Our page on how to reduce rain noise under a flat rooflight goes through them one by one.

The Swan Centre and the pedestrianised High Street came out of a redevelopment in the 1980s, and they changed what the middle of Leatherhead is. If your home is close to streets like that, access is worth thinking about before the job, not during it.

Materials go up by hand or by hoist rather than from a drive, and the order of work is planned around where a van can stand. A sun tunnel can suit a small hallway where a full window cannot.

The survey notes who shares the roof and who shares the wall. A flat with neighbours above has different obligations from a house, and the written spec records them, so that nothing is decided on the day.