How much does it cost to replace a skylight?

The first driver is the unit itself. A roof window, a flat rooflight, a roof lantern and a walk-on panel are different products with different amounts of glass, frame and workmanship in them, so replacing one with another changes the cost before anything else is considered. Size follows close behind: a larger unit needs more material, more handling and a bigger weathering detail.

Within one type, the glazing you pick moves the figure. Triple glazing, a low-emissivity coating or a solar-control coat all add to the unit and take heat loss down, and an opening model with a motor costs more than a fixed one. Frame material matters too: an aluminium frame is slimmer and stronger than a uPVC one, and uPVC is the cheaper material.

A like-for-like swap, with the new unit matching the old in size and position, keeps the work simple. Fitting a larger one means cutting the opening bigger, and a bigger opening alters the roof structure, with rafters or joists trimmed around it. The guide to fitting a larger rooflight in place of the old one explains what that involves.

The size of the old unit is the starting point, and the label or the maker's code on the frame, where there is one, helps to match it. VELUX sizes use a letter for the width and digits for the height, as in MK04, and we check each against the opening on site, since an old roof can have been altered since the window went in.

When only the glass has failed and the frame is still sound, the job can be a new sealed unit instead of a whole skylight, and the guide to skylight glass replacement cost covers that narrower case.

Every unit has to be weathered into the roof around it, so the covering is part of the job. On a pitched roof, slate and tile each take a flashing kit that sits over the roofing, and slate needs more care in cutting and dressing than a concrete tile. Older roofs can add to the work where the slates are brittle or the battens beneath them have softened.

Flat roofs are covered in felt, EPDM or GRP fibreglass, and the upstand round the unit is detailed differently for each. A tired covering around an old kerb can be renewed while the unit is out, so the new rooflight sits in a roof that has been weathered as one piece of work. That adds to the job and saves opening the same roof twice.

Access changes the cost to replace a skylight, because the new unit has to be carried up and the old one carried down. A single-storey extension that can be reached from a ladder is a quicker job than a third-storey slope or a roof that sits above a glazed conservatory, where the way up and the support for the roof need planning.

Something as ordinary as a narrow side passage in a terrace, with no rear access, changes how the unit travels. We look at the route on the survey, along with where the work will stand and what lies underneath, so the way in is clear before the quote is fixed. A roof that can be reached in a straight line from the ground keeps that part of the work short, and one that needs a long carry or extra support adds to it.

The opening in the ceiling or the sloping roof has to be finished, and the finish adds to the cost. Where a unit is replaced like for like, the existing reveal is often sound and needs only touching up. Where the unit gets bigger, or the old reveal is cracked or stained, it is re-plastered.

In a loft the opening can sit at the top of a short light well, a boxed passage of plasterboard between the roof and the ceiling. Angling its sides outwards sends more daylight into the room, and it is extra work to build. Paint and decoration after the plaster has dried are part of the finish, so it helps to say at the survey how far you want us to go.

A price for replacing a skylight cannot be given reliably over the phone, because every item above depends on the roof and the room. The free survey measures the opening, reads the covering, looks at the route to the roof and checks the inside finish. The written quote that follows is a single fixed figure for that room, with the chosen unit and its measurements recorded alongside.

We notify Building Control of a replacement, because swapping a unit is notifiable work; the planning and Building Regulations guide explains why. The finished work carries our ten-year workmanship guarantee.

A replacement figure rests on the same wider list of factors as any other job, which the cost breakdown for a skylight or rooflight goes through in full. If you would like a survey, message us on WhatsApp at 07880 284133 and say which skylight is due to come out. The signs that it is time are listed in when should a skylight be replaced.