Cost of having a Roof Window Replaced

All you need to know about replacing a roof window including costs of materials, costs of labour and time frames.

replace roof window

What the job entails

Contrary to popular belief, Velux is not a generic name for a roof window, it’s the name of a specific company that makes popular type of roof window. There are many other manufacturers and types of roof windows, including roof domes, opening casement windows, sun tunnels and generic roof windows. Most of which can be used on new installations as well as replacements for older roof windows. The light dome type of roof window is available opening and non-opening, but even the opening versions are completely different from a Velux-type roof window.

Roof domes are much cheaper and won’t fully open, often used on flat roofs for extra light. Velux-type opening roof windows are used on sloping tiled roofs. Opening casement type roof windows also have different types of openings, some are hinged at the top of the frame (top hung), while others have the hinge about halfway down the frame. This article will be mainly concerned with Velux type opening roof windows, rather than the cheaper skylight type non opening windows which are really just for some additional light. Installing a window usually means roof timbers will need to be cut which will involve putting extra supports in place, but this does not apply to a "like for like" replacement window. Modern Velux type roof windows offer not just more daylight and fresh air; they can also offer a fire scape exit for emergencies.

When replacing a roof window there are some related jobs that may need doing at same time. For example, cleaning or maintenance of roof tiles, fitting of loft vents, plus of course adding loft stairs if not already fitted. If the loft is not already boarded out, then now would be a good time as this will make it easier to fit the new window and will also allow better usage of the loft space.

Replacing a roof window for a new window of the same type and size is fairly straightforward as a DIY job. There are no major alterations required to the roof, no cutting of rafters if the opening is already in place and no planning permissions or building approval is required. Of course fitting a larger window will involve removing roof felt and tiles, plus cutting into rafters and adding additional support if required. This is a much bigger project and not for the casual DIY enthusiast.

There are a number of potential pitfalls to this job if doing it yourself. Even when just replacing the window with one of similar size, there may be a need to climb on the roof to take off tiles or flashings, or to remove felt or waterproof membrane. Before doing this you need to ensure that there are no pipes, wires or other obstructions in the path of your roof window.

If you are lucky and your new roof window fits between the existing rafters in the existing opening, then it can be just a simple job of fitting the window to the existing woodwork, with perhaps some additional timber framework internally required for new plasterboard and decoration to finish the job off. But if you’re cutting into roof timbers you are potentially weakening the structure of the roof, so you are going to have to notify the planning department, so a planning officer can come down and advise you on keeping the structural integrity of the roof.

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Roof Window Replacement Cost

The average cost of hiring someone to replace a roof window will usually be in the region of £500-£800, although this does not include cost of scaffolding and assumes everything goes fairly smoothly.

Window specialists usually charge around £150 per day and tend to work in pairs for safety reasons. In most cases, the replacement of a roof window shouldn't take any longer than a day to complete and can often be quicker.

Here are a few average costs for hiring someone to replace a roof window:

Window Type Size Avg. Cost Duration
Skylight Small £500 4-6 hours
Roof Dome Small £450 4-6 hours
Velux Small £550 4-6 hours
Skylight Large £700 6-8 hours
Roof Dome Large £650 6-8 hours
Velux Large £800 6-8 hours

Cost Breakdown

Individual costs for hiring a tradesman to install a large velux window - Total Cost: £800






Waste Removal


If we assume a small Velux replacement pine window with laminated glass with a centre pivot, then a typical quote would be in the region of £500, whereas a larger window will cost around £800. This will include the window itself plus the flashing kit, collar and insulation. Assume the quote also includes the removal of all waste including the old window. However, quotes will not typically include any scaffold costs if required, though most windows can be fitted from inside, sometimes this is not possible and a scaffold tower is the only safe option.

In addition, the original window should have been fitted with a vapour barrier, if this has not been done then it will have to be fitted at extra cost to prevent internal condensation. There are also a range of optional extras available for Velux windows which will not be included in any quote unless you specifically ask for them, including security glass, electric openers, shutters and blinds, plus automatic rain sensors.
Typically, around 4-6 hours if everything goes smoothly, assuming a ”like for like” replacement with no structural alterations to the roof required.
Not always, most common spare parts for Velux windows can be changed very easily and they have an extensive spare parts catalogue for all their window types. Velux windows are high quality and designed to last for years, so when individual things wear out or break, you should be able to find and replace the most common spare parts yourself.

Parts available include vent casing, frame cover, striking bead, glass conversion kit, corner brackets, L shaped brackets, ventilation/opening bar foam, casing filter, replacement striking plate, locking mechanism, pivot roof window pivot hinge set, extra strong friction hinge clips hinge spring, lubrication grease, barrel bolt, side railing, side rail pack, replacement gaskets and sash seals.

So unless the roof window is really old and beginning to fail in multiple areas, you should be able to find and replace any minor individual part cheaply and easily. If the glass double glazing unit fails you can get Velux to come and install a new sealed unit for you, or contact them to supply the glass to fit yourself. If there are leaks around the window frame, Velux also sell different flashing kits to suit specific window frames and types of roof. To order any spare parts from Velux, just make a note of the part/serial number that is stamped on the frame of the original window.