Rooflights and skylights in Carshalton, from the ponds to the loft

Carshalton lies in the valley of the River Wandle, and its ponds are among the sources of that river, fed by chalk springs. The water is the reason the town is where it is.

The town sits in the London Borough of Sutton, about 9.5 miles south-west of Charing Cross. Before 1965 it belonged to Surrey, and the older parts still feel more like a Surrey village than a London suburb. The 2011 Census recorded 29,917 residents across three wards, so this is a town of real size, with a good deal of housing packed into the valley and the land around it.

We are based in Crawley, 20.5 road miles away, so a survey here is a planned visit. We arrive with the tape, the ladder and the questions already prepared. A rooflight is a simple idea: a hole in the roof with glass in it. The difficulty is that the roof is the thinnest part of any house. Whatever the weather is doing outside, a badly chosen unit brings some of it indoors. Our guide to what the words rooflight and skylight mean covers the vocabulary, and the rest of this page applies it to Carshalton.

The architecture in Carshalton runs from timber-framed medieval buildings through Victorian streets to modern houses, and it includes Grade II listed and locally listed buildings. That is a wide span for a single town, and it decides how a rooflight job is planned.

A timber-framed building asks for the most care. The roof structure may be the frame itself, hand cut and pegged, and it was never designed around a modern opening. Before anyone proposes a cut, the rafters are looked at, because the position of the opening has to work with them and not against them. On a listed building the work also needs listed building consent, which is a separate matter from ordinary planning permission and is settled with the council first.

A Victorian house is easier in some ways and harder in others. The roof is usually a simple pitched form, which suits a flush roof window. The difficulty is age: slates or clay tiles that have to be lifted and relaid, and timbers that have had a long time to settle. A roof like that is opened course by course, and the flashing is built up with the roof covering so that water runs over it and never under it. Our page on roof window installation covers the units made for pitched slopes.

A rooflight that is too small will not light the room, and one that is too big will overheat it in summer and lose warmth in winter. Sizing is a balance, and our guide to sizing a rooflight for the room shows how it is worked out.

Position matters as much as size. A skylight in the wrong place puts a patch of light on the ceiling instead of the floor, or sits above a bed where morning sun is unwelcome. The guide on where to position a skylight in a room covers this, and it is the first thing we talk through at the survey, standing in the room with the roof above us.

Whatever is chosen is installed to current Building Regulations. That means Approved Document L for the thermal performance of the glass and the frame, Part K for safety, including where a unit can be reached or walked on, Part B where the roof is close to a boundary, and Part F for ventilation. Where the work is notifiable, we handle the Building Control notification. The page on Building Regulations for rooflights goes through each part, and a well-insulated unit is also a quieter one, which is covered under energy efficient rooflights.

A job in a lived-in house is planned so that the opening is never left exposed, the room underneath is protected, and the dust stays where it is meant to.

The survey comes first. We look at the roof from outside and inside, check the structure, listen to the room, and measure. A written quote follows, and with it the quiet spec: a one-page note that says what we heard, what glazing build we propose and why, and how the upstand and seals will be finished. You can read it before you agree to anything, and it is described on the quiet spec page.

On the day, the roof is opened only as far as the work that can be closed in that day. The new unit is set, flashed and sealed, and the room is made good inside. The work carries a 10-year workmanship guarantee, described on our guarantee page.