A roof window is the simplest way to bring natural light into the loft. Set in the plane of the roof, it lets in up to twice as much light as a facade window of the same size, and allows rooms under the eaves to be ventilated effectively. But it is also a sensitive point: a badly connected roof window is one of the most common causes of leaks. For 15 years, Toiture En Ligne has been installing and replacing roof windows in Brussels, Walloon Brabant, Hainaut and Flanders, treating the connection with the roof covering with the same care as the rest of the roof.
Installing a new roof window
Are you converting a loft, creating a bedroom or an office under the roof, or simply looking to light up a stairwell? We advise you on the position, number and size of the windows:
- height: the handle must remain within reach and the view clear, whether you are sitting or standing;
- width: this depends on the rafter spacing, and we avoid cutting rafters unnecessarily;
- glazed area: a good rule of thumb is at least one tenth of the floor area of the room;
- orientation: on a south-facing slope, external solar protection is essential for summer comfort.
When rafters have to be cut, we install trimmers to carry the loads. The structure remains sound, in line with good building practice. If your project includes a full loft conversion, see our loft conversion page.
Replacing an old roof window
Roof windows installed twenty or thirty years ago often have single glazing or poorly performing double glazing, hardened seals and a tired flashing. The signs that a replacement is needed are easy to spot:
- condensation between the panes or drips on the frame in winter;
- draughts around the sash;
- blackened, swollen or crumbling timber;
- damp patches on the ceiling around the window;
- stiff operation or broken hardware.
In most cases, the new roof window fits into the same opening without disturbing the rest of the roof covering. Manufacturers offer replacement sizes that are compatible with older openings. It is also possible to enlarge the opening or add another unit. Our article on how to replace a roof window explains the steps.
Types of roof window
By opening type
- Centre-pivot: the sash pivots around a central axis and the handle is at the top. This is the most common model, ideal when the window is placed high or behind furniture.
- Top-hung: the sash opens outwards and gives a completely clear view. Practical when the window is placed low.
- Balcony window: two sashes that form a small balcony when opened.
- Roof access window: to get out onto the roof, for example for maintenance or chimney sweeping.
By frame
Varnished timber frames give a warm look. Timber frames with a white polyurethane coating are more resistant to moisture and are recommended for bathrooms and kitchens. As for glazing, high-performance double glazing is the minimum; triple glazing further improves insulation and acoustics.
Accessories
External roller shutters, awning blinds, blackout blinds, insect screens, solar-powered motors and rain sensors: well chosen, these accessories greatly improve comfort, especially in summer. The external shutter is the most effective against heat, because it stops the sun before it reaches the glass.
A watertight connection, the key to a good installation
The quality of a roof window depends as much on its installation as on the window itself. We follow the manufacturers’ steps meticulously:
- Cutting the roof covering and, where necessary, the underlay and battens, to the exact dimensions.
- Fitting an insulation collar around the frame, to eliminate the thermal bridge.
- Underlay collar connected to the existing underlay, with a drainage gutter above the window.
- Flashing kit suited to the material: profiled tiles, flat tiles, slates or a metal roof.
- Vapour barrier connected continuously on the inside.
- Interior finishing: lining, sill and reveals, ideally vertical at the bottom and horizontal at the top, to spread the light better.
The right time to install a roof window
If you are planning a roof renovation or roof insulation in the coming years, take the opportunity to install or replace your windows at the same time: the connection is then made under the best conditions and without extra cutting costs.
Roof windows and planning rules
In many cases, installing a roof window in the plane of the roof is exempt from planning permission, especially on slopes that cannot be seen from the street. The rules depend, however, on the region, the municipality and the building: in a conservation area or on a visible slope, limits on number, size or position may apply. We check this with you before the work begins.
How much does a fitted roof window cost?
The price of a fitted roof window depends on its size, opening type, glazing, accessories and the type of roof covering. As a guide, allow the following in Belgium, excluding VAT:
| Work | Indicative price range excluding VAT |
|---|---|
| Replacement in the same opening, standard model | €900 to €1,600 |
| Creating a new opening, standard window | €1,300 to €2,500 |
| Solar-powered external roller shutter | €500 to €900 extra |
| Full interior finishing | on quotation |
These figures are orders of magnitude. For a home that is more than ten years old, reduced VAT at 6% may apply to supply and installation.
Light and comfort all year round
A roof window is more than an opening in the roof: it shapes the comfort of your loft room in every season. That is why we look not only at the dimensions but also at the glazing, ventilation and solar protection that suit your orientation. You enjoy plenty of light without suffering from summer heat.
Why entrust your roof window to us?
- Roofers, not just fitters: the connection with your roof is our trade;
- products from recognised manufacturers, with their warranties;
- a clean job, often completed in a single day for a replacement;
- photos of every stage and a written guarantee on the installation.
Frequently asked questions
How long does it take to replace a roof window?
A replacement in the same opening usually takes half a day to a full day. The room remains protected throughout the work.
My roof window is leaking: does it need replacing?
Not necessarily. The leak often comes from the flashing or a seal, which can be repaired. If the window is more than twenty years old, however, replacement is often the more sensible choice. See our roof repair page.
Can a roof window be fitted in a flat roof?
On a flat roof, we usually install a rooflight or a flat roof window, with an insulated upstand and waterproof upstands. See our flat roof page.
