Question answered
Is it cheaper to put in a window or a skylight?
The short answer
A skylight, meaning a roof window set into the slope, is almost always the cheaper way to bring light into a loft room than a dormer window. MyBuilder's guide, updated on 21/08/2026, gives a typical UK range of £350 to £600 fitted for a standard roof window, with scaffold at around £500. A dormer is a small built structure, priced on survey, and it cannot rely on permitted development in a conservation area.
A roof window set into the slope and a dormer built out from it solve different problems, and they are priced very differently. This page compares cost and permission side by side.
Two different kinds of job
A roof window takes the place of a patch of covering, with a glazed frame sitting level with the slope. The rafters may need trimming, but the outline of the roof stays as it was. A dormer is an addition. A box is built out from the slope with its own floor, cheeks (the side walls), roof and flashings, and a vertical window set into its front face.
The dormer adds headroom and floor area as well as daylight, which a roof window cannot do. That is why the two are not like-for-like, and why comparing prices without comparing what you get can mislead. If the aim is light and fresh air, the roof window is the tool. If the aim is a usable room with a full-height wall, a dormer starts to make sense, and its cost is closer to that of a small extension. The wider range of roof glazing is on our skylights and roof windows hub.
What a roof window typically costs
MyBuilder's Velux guide, updated on 21/08/2026, puts installation at £350 to £600 for standard jobs, covering both labour and fitting. The same guide gives £305 as the average price of a standard centre-pivot window, and about £500 for scaffold. All three describe a plain job and come from a third-party guide, not from us.
They suit an easy position and a straightforward fit. Several things push the total up: a larger frame, a new opening that needs a trimmed rafter, a slate or hand-made tile covering that demands more care, a tall or awkward roof that needs more scaffold, and any upgrade to the glazing. Whoever quotes, check whether scaffold and VAT are inside the total before you compare one with another. Our quote is a single written price, sent once we have surveyed the roof. The difference between unit and fitted price is picked apart in rooflight prices.
Why a dormer is priced on survey
A dormer has no single typical price, because the range of jobs is so wide. It needs structural framing, a new roof over the top, cheeks clad to match the house, flashings, insulation, a window, internal lining and, usually, scaffold standing for weeks rather than days. The size of the box and the condition of the existing roof timbers decide how simple or involved that becomes.
Building control is part of the picture. A dormer alters the structure of the roof, so approval applies, and the energy limits in Part L follow for the new walls, roof and window. Those steps take time and add professional fees on top of the building work. A roof window avoids much of that: the structural change is limited to a trimmed opening, and the glazing standard is a U-value of 1.4 W/m²K or better, or energy Band B. The detail is in roof window building regulations.
Permission compared
Roof windows come under Class C of the permitted development rules. Two limits matter. The frame may stand out no more than 0.15 metres from the plane of the original slope, and the ridge line of the house must remain the highest point. Within those limits planning permission is not normally needed. Class C carries no exclusion for conservation areas or the National Park. A window on a side slope has a further condition, explained on side roof windows and obscure glass.
Dormers come under Class B, which sets a volume limit and, importantly, does not apply on land in a conservation area or the South Downs National Park. Some local Article 4 directions go further, and in two Adur conservation areas, Old Shoreham and Kingston Buci, Class C is withdrawn for roofs facing a highway. Flats have no such rights at all. Before you commit to either option, put the question to the council's planners in Worthing Town Hall, or to the National Park Authority where your house falls under it.
Choosing on more than the price
Start with what the room needs. A landing, a bathroom or a storage loft rarely needs more than a roof window, and one or two will often do. A bedroom brings its own rules because an upper-floor bedroom may need an escape route out. Where you need to stand at the window or fit furniture against a full-height wall, a dormer gains the space that a roof window cannot. Count the number of openings too: three roof windows can end up costing as much as one modest dormer once scaffold and finishing are added.
Then ask who will do the work. A roof window is a standard roofing task, as described in do roofers put in Velux windows, whereas a dormer is a build that draws in carpenters and often an engineer. After our survey you receive photographs of what is on your slope together with the price, so the decision rests on what your rafters and covering will take, not on a catalogue.
Light from the roof: two cost questions
Does a second roof window cost as much as the first?
Usually less per window, because the scaffold and set-up are shared, but not by a fixed amount. Each new opening still needs its own cut, framing and flashing. Windows fitted side by side can sometimes share a combined flashing, which changes the price again, so the survey settles it.
Is a replacement roof window cheaper than a new one?
Generally yes. Swapping a unit into an existing opening avoids cutting and framing a rafter, and the flashing is the main new material. The opening must be sound and the new size must match the old one. If it does not, you are cutting a fresh opening, and the price follows.
Tell us about your roof
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