Ask three people what a flat rooflight costs and you will hear three different answers, all of them honest. A small fixed unit over a utility room and a large opening rooflight over a kitchen island are both called flat rooflights, yet they share very little beyond the name. The price is built from parts, and some of those parts are hidden inside the roof where you will never see them again.
A written quote for a flat rooflight has several separate parts. No figures appear here, because a number quoted without a survey is only a guess dressed up. What you do get is a way to tell a thorough quote from a thin one, and a list of questions to put to anyone who offers to fit one.
Start with the glass unit itself
The rooflight is the largest single line. Its price follows the size of the glass, the type of unit and how it is built. A fixed unit, which does not open, is the plainest option. A unit that opens by hand costs more, and one that opens by motor and closes itself when rain starts costs more again, because of the hinge, the motor and the sensor.
Shape matters less than people expect. Square and rectangular units come off the maker's standard range. Circular, oversized or made-to-order units take longer to build and carry a premium. If your opening already exists and a standard size almost fits, it is worth asking whether adjusting the opening by a few centimetres would let you use a standard unit instead.
Our guide to flat rooflight sizes explains how the opening and the glass relate to one another.
The glazing specification
Within one size, the glazing can change the price a good deal. Double glazing, its inner face coated for low emissivity and its cavity gas-filled, is the usual starting point and meets the standard for rooflights in existing homes. Triple glazing costs more and gives a warmer inner surface. Solar control glass costs more and keeps a south-facing room from building up heat in the afternoon. A tint or a self-cleaning coating each add a little.
We choose a laminated inner pane for overhead glazing, so that if it were ever struck it would hold together rather than fall. Building Regulations do not demand it, but we think it is right above a family kitchen, and it is written on the quote as a line you can read.
| Double, low-E, gas-filled | The baseline most quotes start from |
|---|---|
| Triple glazed | Adds to the price, warmer to stand under |
| Solar control coating | Adds to the price, calmer in strong sun |
| Self-cleaning outer pane | A modest addition, tidier glass after rain |
| Laminated inner pane | Our own choice for overhead safety |
The flat rooflight glazing options guide compares them in more detail.
The upstand under the glass
A flat rooflight sits on a raised kerb called an upstand, built from timber and insulation and normally at least 150mm above the finished roof. It lifts the glass clear of standing water and gives the roof covering something to be dressed up against. Some rooflights are supplied with an insulated upstand already made up at the factory, which adds to the product cost but saves time on site. Others are fitted to a kerb we build to suit the roof.
This is the part of the job people most often ask us to explain, because it is invisible afterwards. A kerb built with thin insulation or poor corners will show itself as condensation on the plaster years later. The price of a good one is the price of the timber, the insulation board, the time to build it square and the time to cover it properly.
Forming the opening
If there is already an opening, the structural work is smaller. If the rooflight is going where no hole exists, joists must be cut and the cut ends carried by new trimmers, which are short beams fixed across the gap. A neat opening that falls between two joists is quick. One that crosses three joists, or sits beside a steel beam, takes more care and more time.
- An opening that matches the joist spacing costs least to form.
- An opening that cuts several joists needs larger trimmers.
- A deep roof build-up needs a taller kerb and more insulation.
- A ceiling that has to be opened up inside adds plastering.
Cutting a fresh hole in a flat roof brings in Building Regulations, which look at the structure and at heat loss, so the quote should name who deals with that and whether the fee is in the total.
The roof it is being fitted to
The covering round the rooflight affects the price more than people expect. Rubber, fibreglass and felt each need a different way of dressing the roof up the kerb. A roof that is sound and recent can be cut and re-formed round the new upstand cleanly. A roof that is old, cracked or nearing the end of its life is a different conversation, and the quote will often show re-covering as an option.
That can feel like a bigger sum than you expected. It is usually less than doing the two jobs apart, because one set of access, one kerb detail and one guarantee cover both. Our pages on the EPDM roof, the GRP roof and the felt roof take each in turn.
Access, protection and waste
Getting glass up to a roof and old material down from it is a real cost. On a single-storey extension reached from the garden, a ladder and a platform may be enough. Where the roof is higher, where the only way through is the house, or where the glass is large and heavy, a scaffold or tower goes up and appears as its own line.
Inside the house, we cover floors, stairs and furniture and screen the work area where we can. Each working day ends with the roof closed in against rain, and the waste leaves with us. These are part of how every job runs, so they sit inside the price rather than being sold back to you as extras.
Finishing the room
From inside, you see the lining between the ceiling and the glass far more than the glass itself. Boarding, plastering and finishing that reveal is part of a proper fit. Splaying the sides so they widen towards the room spreads the light and takes a little longer than straight sides.
Lighting is worth settling before the ceiling is closed. Cables for LED strips or downlights round the opening are simple to run while the joists are exposed and awkward to add afterwards. Painting is usually offered as a choice: some households prefer to do it themselves, and the quote should let you opt in or out.
Planning and Building Regulations costs
On a house, a rooflight usually falls under permitted development, provided it projects 150mm or less from the roof plane and stays below the ridge line. Flats and maisonettes have no such right, so they need planning permission, and a listed building needs listed building consent. Any application carries a council fee. The conditions are laid out in full in the skylight planning permission guide.
If the old unit comes out entirely and a new one goes in, that counts as a controlled fitting and must be notified; a sealed glass unit on its own does not. Any brand new hole in the roof needs approval as well. Where notification applies we handle it, and the building control fee belongs in your sum.
Options that arrive after the glass is in
Some of the most common additions are easy to price at the survey and fiddly to add later. Blinds are the obvious one. A blind made for your exact rooflight runs in side tracks and holds its position, but the maker can only cut it to the glass size if the order is placed with the unit. Fitting one afterwards usually means a standard size that does not quite suit.
Electric opening is another. If you think you may want fresh air through a kitchen ceiling, the power supply and control cable are best run before the plaster goes on. Adding them to a finished ceiling means cutting into it again. Our electric rooflight cost page covers that side in full.
Think about how the room is used across a whole year, not only on a bright morning. A south-facing extension may need shading in July. A dark utility room may only need the light. Telling us this at the survey lets each option appear as a separate line you can accept or leave, and nothing is added on the day without your agreement.
Keeping the glass clean is a small running cost rather than a fitting one. A rooflight over a tree or a busy road collects dirt faster, and you may want a way to reach it safely. It costs nothing to ask us how the glass will be reached before the order goes in.
Replacing an existing rooflight
A like-for-like swap can cost less than a new opening, because the hole is already formed and the joists are already trimmed. The saving is not guaranteed. The old unit has to come out carefully, the kerb has to be examined, and many older kerbs were built low with little insulation. Setting a new unit on one of those simply carries the old cold edge over to the new glass.
When the kerb is sound and tall enough, we insulate and re-dress it. When it is not, we rebuild it, which adds to the sum and is the only route to a dry, warm result. If only a sealed unit has misted and the frame is sound, replacing the glass alone is a smaller job, and our misted and failed rooflights page covers it.
Comparing quotes sensibly
When two quotes differ, the total tells you very little. Lay them next to each other and look for what the lower one leaves out. A thinner kerb, a plainer glass specification, no plastering of the reveal, a roof covering simply cut round, or no mention of Building Control can all hide in a smaller number.
Useful questions to ask anyone who quotes:
- What is the glass build, pane by pane?
- How tall is the upstand and what insulates it?
- What happens to the roof covering where it meets the kerb?
- Is the reveal plastered, and is painting included?
- Who arranges Building Control and who pays the fee?
- What does the guarantee cover?
Every cost on our quote sits on a separate line, and a plan for each day of the fit comes with it. Book the free survey with the form below, or read more on the flat roof rooflights page. If an existing roof is your starting point, adding a rooflight to an existing flat roof explains the order of work.