Ask three people what their roof window cost and you will hear three very different answers, all of them honest. The window itself is a catalogue item with a known price. Everything around it is not. The roof it goes into, the room underneath, how the house is reached and what has to be done to the ceiling all change the total, sometimes by more than the glass is worth.
A written quote usually runs in the same order as the job: the window, how it opens, the flashing, the opening, the lining, the access and the paperwork. Without seeing the roof any figure would be a guess, so none is given here. Knowing what each line is for lets you compare quotes properly and ask the right questions.
The window unit
The first line on a quote is the window. Its price follows the size, the opening style and the glazing. A small window in a standard finish costs the least. Larger sizes cost more, and so do finishes such as a white-painted timber frame or a polyurethane-coated one for a bathroom or kitchen, where steam is part of daily life.
Glazing is the other lever. A standard double-glazed pane with a low-emissivity coating meets the thermal rules for an existing home. Upgrades such as triple glazing, laminated panes for added overhead safety or tinted and solar-control glass cost more, and each should be itemised separately, so the price of every upgrade is visible.
If you are unsure how sizes are labelled, our VELUX window sizes guide explains the code on the data plate, where the letter gives the width and the digits give the height.
Opening style and controls
How the sash moves also shifts the price. A centre-pivot window is the usual choice and the simpler product. A top-hung window, which swings out from a hinge at the head, costs more but suits some rooms better. We compare the two in detail in top-hung or centre-pivot roof window.
Electric opening and rain sensors are further options. They suit windows set out of reach above a stair or a bath, and they need a power supply routed to the frame. That cable run is labour as well as product, so ask for it to be shown separately.
Flashings and the roof covering
Every roof window needs a flashing kit made for the roof covering around it. Slate, plain tile, interlocking tile and pantile each need a different kit, and the kit is a real cost in its own right. Where the covering is unusual or sits on a deep profile, the kit can be one of the larger items.
| Roof covering | What changes on the quote |
|---|---|
| Natural or fibre-cement slate | Thin covering, so the kit is light, but slates must be lifted and cut with care |
| Plain clay or concrete tile | More lifting and relaying, and spare tiles for the cuts |
| Interlocking concrete tile | Deeper profile kit and larger tile cuts |
| Clay pantile | Deep wave kit, and a dry run to find a clean line for the cuts |
The roof also affects labour. An old roof with brittle slates or tiles that no longer match takes longer to work round, and that time is priced. We cover the detailing in roof window flashings for slate, tile and pantile.
Cutting the opening and framing it
When a window replaces an old one of the same size, the opening already exists and the job is lighter. A brand-new window needs rafters cut and carried by new trimmers, and those timbers are sized for the span, so a wide opening costs more than a narrow one that sits between two existing rafters.
Fitting the window between rafters at the standard spacing is quicker than cutting across several. If you have a choice of position, the survey will show how moving a window a hand's width sideways can save a trimmer. We do the hidden timber and membrane work carefully and photograph it before it is covered, and the photos are part of your handover.
Lining the opening inside
From the room, you see the lining more than the glass. The sloping box between the ceiling and the window needs insulation, board and plaster or a prefabricated lining, then a coat of paint. A lining kit made for the window is faster than building one from boards and often looks neater.
Plastering and decorating are usually offered as options. Some owners want the room finished the day we leave. Others prefer their own decorator. Either way, price each choice separately on the quote.
Access: ladder, platform or scaffold
A single window on a low rear slope may need only a roof ladder and a working platform. A terrace three storeys at the front, or a roof reached through a narrow passage, may need a scaffold or a tower, and that has to be hired, put up, checked and taken down. Where a house stands on a steep street or has no garden, the cost of reaching the roof can be a visible line on its own.
Ask whether scaffold is in the price, and whether it covers the whole job or only part of it. A quote that leaves it out may still have to add it later.
Protecting the house and taking waste away
Dust control is a real part of the cost of a job done inside a home that is being lived in. Floors and stairs are covered, furniture is moved or sheeted, and dust sheets hang across the working area wherever the layout allows. Each evening the roof is closed in and made weathertight, so that rain overnight does no harm to the room below.
Old window frames, slates, plasterboard and packaging are taken away at the end, not left in a skip bag in the garden. These tasks cost time, and a quote that lists them is telling you the house will be treated with care.
Planning and Building Regulations
Most roof windows on a house are permitted development, so no planning fee applies. The conditions are in our skylight planning permission guide. Flats and maisonettes need an application, and listed buildings need consent, and either adds a fee and a wait to the job.
Building Regulations are separate. A new opening needs approval for the structure and thermal performance, and a whole replacement window is a controlled fitting that must be notified. Either the council's building control team or a registered building control approver deals with it, and their fee is part of the real cost. We arrange the notification and give you the paperwork at handover.
Replacing against adding
Replacing an existing window is usually the lighter job. The opening, the trimmers and often the lining are already there. What you pay for is careful removal, a check on the condition of the timber round the old frame, a new flashing kit and the window. Where the old window was fitted without a proper membrane or insulation, correcting that adds time, but it is the work that protects the room.
Adding a window to a roof that has none involves everything above: the opening, the framing, the lining and a new line of paperwork. That is why the same window can look cheap in one quote and expensive in another: one quote is for a swap, the other for a new opening.
Several windows at once
Fitting a pair or a row in one visit usually costs less per window than fitting them separately, because the access, the protection and the paperwork are shared. A pair of windows side by side can also be set on one pair of trimmers with a short length of rafter between them, though the surveyor will confirm that against your roof.
If you are planning a loft room, deciding how many windows you want up front is cheaper than adding another in a year. We look at that in roof windows for loft conversions.
Blinds, shading and extras
Blinds are the item most often added as an afterthought, and they are cheaper to specify at the start. A blackout blind suits a child's bedroom or a room used for sleep in daytime, a pleated blind softens the light in an office, and an external awning blind cuts heat before it reaches the glass. Each is made to fit a particular window size, so ordering them with the window avoids waiting later.
Some extras are far cheaper to add while the scaffold is up or the ceiling is open: a ventilation flap above the sash, a second window for cross-breeze, or a cable for an electric blind. They cost little at the time and a good deal more once the lining is painted. Our VELUX blinds and accessories page lists what is available.
Timing and what it does to the price
Some costs depend on when the job happens. Slate and tile can be worked in most weather, but wet or windy days slow the roof work, and a day lost to rain is a day of scaffold hire that still has to be paid. Booking a job in a quieter part of the year does not change the product price, though it can make it easier to agree a start date that suits you.
Lead times play a part as well. Standard sizes are usually available quickly, whereas a made-to-order size or an unusual finish may take longer to arrive. We set a fitting date once the product is confirmed, so the team arrives with everything on the day and the roof is not left open while a part is awaited.
What the quote should not hide
A fair quote has no vague allowances. If the figure for a flashing kit says only "materials", you cannot tell what you are getting. If the lining says "finish", you cannot tell whether that is bare board or a plastered, painted reveal. Ask for the detail until each line says what is done, in what material and by whom.
It is also fair to ask what happens if the survey and the roof disagree. Sometimes a rafter is found to be in poorer condition once the slates are lifted. The right answer is that you are told straight away, shown a photograph and given the choice, with a clear figure for any extra work, rather than being presented with a larger bill at the end.
How to compare quotes
Line up the quotes next to each other and check that each one covers the same things. A lower total often means something has been left out: the lining, the scaffold, the building control fee, the removal of waste or the flashing kit for your roof type.
These questions are worth asking of any installer:
- Which flashing kit is allowed for, and is it right for my roof covering?
- Is scaffold or a tower included, and for how many days?
- Is the lining plastered and painted, or only boarded?
- Who notifies Building Control, and is the fee in the price?
- Is the roof closed in each night?
- How long does the guarantee on the labour last, and what is excluded?
Our written quote answers each one, itemised line by line, with a plan for each day. There is no charge for the survey, and the fuller story is on our roof window installation page, or you can book using the form below.