How much does a flat rooflight cost to fit?

A flat rooflight is a glazed unit set up on a kerb over a flat roof. Four choices about the unit move the figure more than any others.

• Size. A larger unit is dearer to make, and it asks more of the roof and the ceiling around it.
• Glazing. VELUX lists double or triple glazing for its flat and curved glass rooflights, and what is available depends on the product.
• Fixed or opening. A fixed unit is the simplest. An opening one has more to it, and an electric opener brings a motor that needs power.
• Finish. Self-cleaning glass exists as a rooflight option, and Pilkington lists roof glazing among the uses for its self-cleaning coating.

Size also affects the room. A wide unit over a dining area lets in a great deal of daylight by day, and the same glass reads black and mirrors the room after dark, so the size you pick is worth thinking about for the evening as well as the morning.

Our guide to fixed and opening units goes through that choice in detail.

Swapping a unit that is already in the roof is a smaller job than cutting a new one. A sound kerb of the right size can take a new rooflight directly, which our answer on replacing a flat rooflight explains.

A new opening brings the structure into it. Usually the roof structure needs altering to form the opening, and the roof must be strong enough for the rooflight's weight, or be strengthened so that it is. A kerb is built, and inside, the opening is lined and the ceiling made good.

Where the old kerb is the wrong size, or the covering at its foot has worn, some of that work comes back even on a replacement. A rooflight over a bathroom or a utility room is no different from one over a living room in this respect, because the roof decides it.

If a home already has a rooflight that is giving trouble, our piece on what a replacement costs looks at that case, where the opening is already there and the question is what has to change around it.

Water has to leave a flat roof, and a kerb that lets it pool is a poor base. For its flat glass rooflights, Rainclear advises a kerb slope of at least 5 degrees, which is one reason the roof gets looked at before a unit is chosen.

The covering around the opening also shapes the price. It meets the kerb, and an old or worn one can need more attention than a sound one.

Access finishes the picture. A low extension roof can sometimes be worked from ladders with a working platform. A tall rear elevation or a roof with no side access can call for scaffolding, and the survey sets that cost against the job.

Those three, the falls, the covering and the access, are checked on the roof itself. A photo from the ground cannot tell us how the roof drains or how a large unit would be carried up, which is why the visit comes first.

In Wales, Building Regulations approval is generally needed when a new rooflight goes in. Where the work is notifiable, we handle the Building Regulations notification with local authority building control or a registered building control approver.

Planning is a separate check. Whether a flat rooflight fits within permitted development depends on how far it stands above the original roof and on where the house is, and our answer on planning for flat rooflights takes it step by step. The guide to Building Regulations in Wales covers the approvals side, and either one can add time before work starts.

The things that settle the price sit above the ceiling: the joists, the kerb, the covering and the way up. A message cannot show them. We come out, study the room and the roof together, take measurements, and put the figure in writing as a fixed written quote.

A 10-year workmanship guarantee is given in writing too. For a wider view of what rooflights involve across the range, what shapes a price in Newport sets the products side by side, and the booking route is the survey form.

If your roof sits on a listed house or inside a conservation area, say so when you book, because a planning application or listed building consent can then be needed before work starts.