Velux installation:
prices and steps.

Velux is a registered trademark; in everyday use, the word refers to all roof windows, whatever their manufacturer. This guide therefore talks about a roof window, with no brand preference: the model is chosen according to the pitch, the roofing material and the use of the room.

It is fitted in the plane of the roof slope. It creates neither volume nor headroom: it brings light and air into a room that already exists, or into a loft that is about to be converted. When headroom is what is missing, the answer is rather a dormer, a structure on another scale that we describe in our dormer guide.

Because it is tilted towards the sky, a roof window receives more light than a vertical window of the same size, but also more sun in summer and more snow in winter. These three effects decide its position and its equipment far more than the catalogue does.

The two jobs go by the same name, but they have neither the same content nor the same tax framework.

Creating a roof window means interrupting a roof covering and insulation that were continuous. The underlay has to be cut, sometimes a rafter cut and a trimmer fitted to take up its load, then the waterproofing and insulation rebuilt all around the opening. It is as much roof carpentry and roofing work as joinery.

Replacing a roof window that leaks, no longer closes or lets the cold in is simpler when the new one keeps the dimensions of the old one: the opening in the roof structure already exists. Depending on the condition of the frame and the flashing, the whole window is changed or part of the existing one is kept. If you use the replacement to enlarge it, you are back to the creation case, roof structure included.

The distinction also matters for VAT, as we explain below: the reduced 5.5% rate applies to replacing an existing window, not to creating a new opening.

1. The survey. Under the roof slope, we measure the rafter spacing, the pitch, the insulation thickness and the height at which you want to see outside; on the roof, we look at the roofing material and its condition. These measurements set the possible size of the window and its position.

2. The formalities. The prior declaration is filed before anything is ordered: the window is only delivered once the town hall has given its approval, which avoids storing a model that has been refused.

3. Opening the roof. Our carpenters remove the tiles or slates over the area, cut the underlay and open up between the rafters. When the window is wider than the space between two rafters, they cut one and fit a trimmer that transfers the load to its neighbours.

4. Fitting and flashing. The frame is fixed to the roof structure, then the flashing, specific to each type of roof covering, is put in place and the covering is closed up around it. It is this detail, more than the window itself, that decides whether the opening will stay watertight winter after winter.

5. Insulation and airtightness. On the inside, insulation is added against the frame and the vapour barrier is connected to it without a break. A neglected junction at this point is paid for in condensation on the frame and marks on the ceiling.

6. The lining. Our plasterers line the opening in plasterboard, splaying the sides to spread the light better through the room, before the finishes.

Installation prices shown online almost always rest on an unstated assumption: a standard window, slipped between two rafters of an accessible tiled roof, with no interior making good. As soon as one of these parameters changes, the figure no longer holds. We therefore do not publish an average price; instead, here are the lines that a complete quote must show.

Supply: dimensions, opening type, manual, electric or solar operation, glazing, and interior or exterior blackout accessories.

Flashing, chosen according to the roof covering: interlocking tiles, plain tiles, slates or steel sheet. A recessed installation, more discreet in the slope, requires a specific flashing.

Roof structure: nothing to do if the window fits between two rafters, a trimmer if it is wider, more if the exposed timber is damaged.

Access: work from inside the loft, or scaffolding and protection when the roof is high, very steep or inaccessible from inside.

Interior: added insulation, vapour barrier, lining, painting. A “fitting only” quote often stops at the frame and leaves this item for you to pay.

Removal and formalities: removal and disposal of the old window in the case of a replacement, preparation of the prior declaration file.

To compare two quotes, first check that all these lines appear; only then does the total mean anything. And if your roof covering needs redoing in the coming years, fitting the roof windows during the roof renewal shares the access and the removal instead of paying for them twice.

Creating a roof window, or replacing the existing one with a different model, changes the external appearance of the house: a prior declaration (déclaration préalable) is required. A building permit is required if the installation is part of a change of use, such as converting an old barn into a home (service-public.gouv.fr).

The town hall has one month to process the file, two months near a historic monument or in a heritage site, where the ABF heritage architect gives an opinion. When the window goes with a loft conversion, it is the floor area created that sets the type of permission: the thresholds and the documents for the file are in our prior declaration guide, and the overall project in our article on convertible lofts.

The Civil Code also protects the neighbour's privacy. A roof window that gives a direct view onto their land must be at least 1.90 m from the boundary; if their property can only be seen by leaning out, the distance drops to 0.60 m. A written agreement from the neighbour allows this to be waived (articles 675 to 680 of the Civil Code).

Local regulations can go further than these national rules. In Chambéry, within the AVAP perimeter, the roof window must not project: it is rectangular, fitted vertically, with an area of less than 0.8 m², and lines up with the openings of the façade; on a protected building, no more than two, not adjacent, are allowed per 25 m² of roof (see our page on roof renovation in Chambéry). Before talking about size, we therefore read your municipality's local plan (PLU).

On mountain and foothill roofs, snow lingers on north-facing slopes. A window placed just below a valley or at the foot of a long slope receives everything that slides down. We place it rather in a clear part of the slope, away from valleys and roof outlets, with a flashing chosen for the actual pitch and material of the roof.

In summer, the tilt that lets the light in also lets the heat in. For a bedroom under the roof, external solar protection, a roller shutter or blind, stops the radiation before the glass: this is often more effective than higher-performance glazing fitted on its own.

In winter, the window is the coldest point of the roof slope. If the vapour barrier is not connected to the frame, water vapour from the room condenses in the insulation around the opening. This defect cannot be seen at handover and is discovered in the first winter: we treat it as a stage of the work in its own right.

VAT at 5.5%. Since 1^st January 2025, the reduced energy-renovation rate applies to replacing an existing roof window with an insulated-glazing window whose Uw coefficient is at most 1.5 W/m².K and whose solar factor Sw is at most 0.36 (article 30-0 D bis of annex IV of the French General Tax Code). The home must have been completed more than two years ago.

VAT at 10%. Creating a roof window in a home more than two years old is in principle subject to the rate for improvement work. Our article on VAT on renovation work explains how a quote separates the lines when a job combines both rates.

MaPrimeRénov'. Since 1^st September 2026, the per-measure route has been refocused on heat pumps: the insulation flat-rate grants, which covered window replacement, are no longer available (Anah, grants guide, September 2026). A roof window can still be funded as part of a major renovation, reserved for homes rated E, F or G, which combines at least two insulation measures and gains at least two energy classes. This route must go through Mon Accompagnateur Rénov', an independent third party.

We are certified RGE CertiRénov (no. CR-2026-73-0095). Grant rules change often: check your situation on france-renov.gouv.fr before signing a quote.