Ask what a misted rooflight will cost and the honest first answer is another question: what has actually failed? Sometimes the answer is a single pane of glass in a frame that is otherwise sound. Sometimes it is the frame, the upstand beneath it and the weathering round the edge. The two jobs sit a long way apart, and the haze looks identical from the room.
The cost of a misted rooflight job moves with a handful of items, and they appear in the same order on our written quotes. It gives no figures, because a figure without a survey would be a guess. What it can do is show you what you are being asked to pay for, so that two quotes on your table can be compared line against line.
Start with what has failed
Everything else follows from one question. A misted unit has lost the seal that kept its two panes sealed from damp air, and that is a fault in the glass. The frame around it may be perfectly well. If it is, the job is a new sealed unit made to fit the frame already there.
If the frame has cracked, bowed or corroded, or the upstand under it is low and cold, then new glass in the old frame would only move the problem along. The job becomes a whole new rooflight, and the cost reflects a new frame, new glass and the building work around them. Our guide to a new sealed unit or a whole new rooflight explains how that choice is made.
Where a sealed unit job lands
Replacing the glass alone is the lighter route. The old unit comes out, the rebate is cleaned back, and a new unit made to the measured size goes in with fresh gaskets or sealant. The frame, the upstand and the roof covering stay as they are.
The cost of that route rests on a short list of things.
| Size of the unit | Larger panes cost more to make and take more hands to lift |
|---|---|
| Glass specification | Low-emissivity coating, gas fill, laminated inner pane, any solar control |
| Shape | Square units cost less than curved, angled or odd-sized ones |
| Number of units | Several in one roof are often cheaper to do together than one at a time |
| Reaching the roof | A ladder, a tower or a scaffold, as the survey decides |
Because the glass must match the opening to the millimetre, the unit is made after we measure. That is part of why a survey comes before a quote.
Where a whole rooflight lands
A whole new rooflight adds the frame, a check of the upstand and the work to weather the new frame into the roof. The rooflight is bought as a product, so its own cost depends on size, frame material and glass. Opening versions cost more than fixed ones.
Then comes the building work. The old frame is lifted off, the upstand is examined, and if it is low, damp or poorly insulated it is rebuilt or raised. Flat rooflights are set on an insulated kerb that normally stands 150mm or more clear of the finished roof, so a kerb that falls short is part of the price. The roof covering is then dressed up and over it.
The plastered or boarded reveal inside the room is often disturbed by a larger job, and finishing it is a line of its own. For a plastic dome or sheet, where there is no sealed unit to save, a glass rooflight is the usual route, and our page on replacing a polycarbonate rooflight with glass covers what that involves.
The roof around the rooflight
A new unit is only as dry as the weathering that surrounds it. When we survey, we look at the felt, rubber or lead where it meets the frame, because tired material there can undo a good new pane.
If the covering is sound, it stays untouched and costs nothing extra. If it has split at the upstand or lifted at the edge, we say so and put it on its own line. You can then choose to have it dealt with during the same visit, which saves a second set of access, or to leave it. Either way you decide with the figures in front of you, rather than meeting a surprise once the glass is in.
Roof questions that move the total
- Is the covering felt, rubber or fibreglass, and what condition is it in near the frame?
- Is the upstand tall enough, dry and insulated?
- Is any timber at the kerb soft or stained?
- Do the flashings need lifting to fit the new frame?
Getting to the roof, and the weather
Many rooflights sit on a single-storey roof that a ladder and a roof platform can reach from the garden. Others are on a higher slope, over a stairwell or behind a boundary wall, where a tower or scaffold is the safe way up. Whichever applies is shown as a separate line, so you can see what it adds.
Bear in mind that a glass unit is heavy and awkward to carry. Large panes are lifted rather than walked up a ladder, and the way they travel affects how many people the job needs. Our answer on whether you need scaffolding to replace a rooflight covers the point in more detail.
Protection for the house and the wider job
The work is above your head, but the dust and the footfall are in your rooms. Floors, stairs and furniture below the rooflight are covered and the work area is screened where possible. Each evening, before the team goes, the roof is covered and made safe from rain, and waste goes with us when we finish.
These are part of how every job is done, so none is added to the quote as an extra. Each appears in the written plan, so you can see how your home will be looked after before the date is set.
Timing, lead times and the season
Because a replacement unit is made to size, there is a gap between the survey and the day of the fit. Standard sizes and common specifications arrive sooner, and unusual shapes or special glass take longer. The date is agreed once the order is placed, and the plan for the day is written down.
Weather affects the job more than the price. Glass is not set in heavy rain, and a roof is not left open when the forecast turns. If a day is lost, we rearrange it with you, and nothing is left half done overhead.
Rules, notification and paperwork
Replacing a sealed glass unit alone is not notifiable under the Building Regulations. Taking out the frame as well as the glass makes the job a controlled fitting that has to be notified, and we arrange the Building Control notification. The fee belongs to that job and is shown on the quote.
New glass in an existing frame is a like-for-like swap, so planning permission does not normally enter into it. A different style of rooflight, or one that stands proud of the roof, is another matter, and our skylight planning permission guide explains where the lines are. Our short answer on whether replacing a rooflight is notifiable sets out the difference between the two routes.
What the glass will do for the room afterwards
A failed unit has lost the gas that gave it its insulating value, so the room beneath has been losing heat through it. A new unit restores that. Where we fit a whole rooflight, it is specified to meet the Part L figure for rooflights in existing homes, 2.2 W/m²K.
That is the side of cost nobody puts on a quote: the room that was dim and chilly becomes one you use again. We do not put a number on what it does to a bill, because that depends on the house and how it is heated. We would rather you judged it from the room than from a promise.
Doing several rooflights at one visit
Houses with more than one failed unit raise a fair question: is it cheaper to do them together? Usually the saving comes from the shared parts of the job. One set-up of ladders or a tower, one round of floor protection, one clear-up and one visit to arrange Building Control notification can serve every rooflight in the roof.
The glass itself is made per unit, so the biggest saving is in labour and access rather than in the panes. If one rooflight has misted and its neighbour is only beginning to haze, it can be worth pricing both and then deciding. We lay them out as separate lines, so you can see what each adds and choose.
Choices that add to the total, and choices that trim it
Most of the cost is fixed by the condition of what is there. A few decisions are yours, and they are best made at the survey, when the options can be priced side by side.
- A laminated inner pane, solar control glass or a self-cleaning outer pane add to the unit's cost
- Choosing a standard size over a special one trims it, where a whole rooflight is going in
- Opting for a fixed rooflight rather than an opening one trims it, and ventilating by another route may suit the room
- Leaving the decorating to yourself trims the finishing line
None of these changes the quality of the hidden work. The upstand, membrane and flashings are done carefully and photographed whatever you choose, and the photographs are given to you at handover.
When waiting costs more than doing the job
A lightly misted unit in a seldom-used room can sit for a while. A unit where water is showing at the edges, or where the frame is moving, is a different case, because damp reaches the upstand and the ceiling lining. Deferring a job like that tends to enlarge it.
We would sooner tell you honestly that a job can wait than hurry you into a booking. The questions in our guide on the signs a rooflight has failed help you judge which case you are in.
Reading the quote you are given
Our survey is free and leads to a written quote that itemises every cost separately, together with a plan for each day of the fit. Lay any other quote beside it and look for the same things.
- The size and make-up of each new unit, pane by pane
- Whether the frame is kept, or replaced, and why
- What happens to the upstand and the roof covering around it
- How the roof is reached, and what that adds
- Whether Building Control notification is included where it applies
- What the guarantee covers: ours is a 10-year workmanship guarantee, with the makers' warranties handed over on the day
For the full picture of how we approach these jobs, see misted and failed rooflight replacement, or book a survey using the form below.