The short answer
Replacing a skylight is priced from five parts: the new unit, the glass specification, the flashing or upstand around it, any work to the roof finish and the lining inside, and the survey findings that decide whether the old frame stays or goes. A written quote prices each part for more than one suitable unit, so you can see where the money goes.
Whole unit or glass only
The first decision moves the price more than any other. With a frame that is still serviceable and only the sealed glass failed, a fresh glass unit in the existing frame usually costs less than a whole new rooflight. If the frame is worn, the seals around it have perished or the unit no longer suits the room, replacing frame and glass together costs more and gives you a new product with a new maker's warranty.
Renewing just the sealed glass unit sits outside the notification rules of the Building Regulations. A complete rooflight changeover, frame and glass, is a controlled fitting and so has to be notified, and when it does, we make the notification to Building Control ourselves. The difference between the two is set out in our guide to rooflight replacement and the Regulations, and how we tell a failed unit from a failed frame is covered on our page about replacing misted rooflights.
Like for like or an upgrade
A unit of the same size, type and glass as the one it replaces is the lower-cost route, because the opening, the flashing and the lining inside are already in place. An upgrade changes one or more of those things, and each change adds to the figure.
| Item | Usually lower | Usually higher |
|---|---|---|
| Scope | Sealed glass unit only | Whole unit, frame and glass |
| Size | Same as the old opening | A larger opening |
| Glass | Double glazed, plain | Triple glazed or coated |
| Opening | Fixed, or the same vent as before | Electric vent with rain sensor |
| Type | Same product again | A different type of unit |
Changing the opening size is the step that adds most, because it means cutting rafters or joists, framing the new opening and making good the roof finish around it. A new or larger opening counts as building work for the Regulations, so a structural check and a Building Control notification each get a line of their own on the quote.
The glass specification
Double glazing is the starting point for most replacements. Triple glazing adds cost and weight, and a solar control coating adds cost too. On a south or west facing roof that coating often does more for comfort than a third pane. A self-cleaning outer pane is another option that changes the figure, and it suits roofs you cannot reach easily.
A new rooflight has to meet the current Building Regulations limits, which is one reason an old unit is rarely matched exactly. Our page on energy-efficient rooflights compares the glass options on the same measures.
Flashing, roof finish and the lining inside
Every rooflight sits in a flashing, upstand or kerb that keeps water out, and the quote shows that part as its own line. On a pitched roof the flashing kit is matched to the covering, whether slate, plain tile or profiled tile. On a flat roof the upstand is built up and the membrane is dressed to it.
If the roof covering around the old unit is worn, joining new work to it can mean replacing a larger area than you first expected. The survey will show whether that is likely, and the quote keeps the extra area separate so you can decide.
Inside, the lining of the light shaft is part of the job on a replacement more often than most people expect. A new unit of a slightly different size leaves a gap to fill, and the plaster and paint around it are usually left for you to finish unless you ask us to price them.
Access and the make
Scaffold or a tower, and how far the unit has to be carried, can add a line to the quote on a tall house or a roof over an extension. A unit that is stocked by the maker usually costs less and arrives sooner than one made to order, and our answer on how long skylights take to arrive explains the difference.
We are not tied to one maker. Where the roof allows, units from several makers are placed in rows on the quote, so glass, frame, opening and price can be compared line for line. If your old unit is a VELUX, our page on replacing an old VELUX window goes into that case in more detail.
Why replacement pricing starts with a survey
Two replacements that look identical from the garden can differ a great deal once the frame, the flashing and the roof finish are examined. A figure given without seeing the roof is a guess, which is why the survey is free and the quote sets out each part for each option.
- Glass unit and whole unit priced separately
- Flashing and roof finish shown as their own lines
- Maker's lead time stated on each option
Whenever you are happy to proceed, book a free survey, and the units that suit your roof will be priced next to each other. Our home page lists every kind of work we quote, from new openings to like-for-like swaps.
Related questions
Is it cheaper to replace just the glass?
It usually costs less than a whole new unit, provided the frame and the seals around it are sound. We look at the frame at the survey and say which route makes sense.
Does the quote include Building Control?
When the job needs notifying, we make the notification and list its fee on the quote. A glass-only replacement is not notifiable.
Will a new skylight cost more than my old one did?
Often it does, because the glass now has to meet current limits and the flashing and lining may need work that the first fitting did not. The quote lists each part so you can see which is which.
Can I choose between makers?
Yes. Where the roof allows, units from several makers appear on the quote together, with their glass, opening and lead time.