A roof window (dakraam) is one of the simplest ways to make a dark attic usable. Daylight comes in, you can ventilate and the intervention is much smaller than with a dormer. In everyday speech a roof window is often called after the best-known brand, but there are several manufacturers and designs. This article explains which types exist, when a roof window or rooflight is permit-free, what changes for a listed building, in a protected townscape or village view, or in a flat, how a carpenter builds the window in so that it is structurally sound and watertight, why a roof window can leak or mist up and what to have recorded in the quote.
Roof window, skylight or dormer?
A roof window, also called a dakvenster (skylight), sits in the plane of a pitched roof and follows the roof slope. It provides light and air, but no extra headroom. A dormer (dakkapel) is a structure that projects from the roof plane, with its own flat roof and a vertical window; that does provide headroom and floor space, but it is a larger renovation with stricter rules. If you are torn between the two, also read Fitting a dormer: permit-free or permit required? In a flat roof people speak of a rooflight (daklicht), a dome light (lichtkoepel) or, for an elongated strip of glass, a continuous rooflight (lichtstraat).
Centre-pivot window
A centre-pivot window turns on a horizontal axis roughly halfway up the window. The window opens with the top going outwards and the bottom inwards, and the handle is usually at the top. Because you can rotate the window a long way, you can clean the outside of the glass from inside. Because the handle is at the top, a centre-pivot window is suitable if there is furniture under the window; the bottom of the window does swing inwards a little when opened.
Top-hung window
A top-hung window is hinged at the top and opens outwards as a whole. You then have an unobstructed view without a rotating window section in front of your face. With this type the handle is usually at the bottom, which is handy if the window sits somewhat higher in the roof. There are also combinations that both pivot and open outwards.
Options: ventilation flap, operation and glass
Many roof windows have a ventilation flap in the top rail, so you can ventilate while the window is closed. If you want a window that is high up and out of reach, an electrically operated window can be the answer, often with a rain sensor that closes the window when it rains; for a mains-powered version you need an electrician; there are also solar-powered versions without wiring. Pay attention to the glass as well: insulating glass such as HR++ or triple glazing keeps heat in and reduces condensation on the glass. More on the differences can be found in Replacing glass: HR++ or triple glazing.
When is a roof window permit-free?
Under the Omgevingswet (Environment and Planning Act) there are two tests: the technical building activity (does the window comply with the building-technical rules of the Besluit bouwwerken leefomgeving, the Bbl or Dutch Building Decree) and the environmental plan activity (does it fit within the spatial planning rules). For both, a national exemption applies to daylight provisions in a roof.
For the technical part, Article 2.27(2)(b) Bbl literally mentions "a roof window, rooflight, continuous rooflight or similar daylight provision in a roof". You do not need a technical permit for it. That does not mean no rules apply: the window and the alteration to the roof must still comply with the Bbl, and the municipality can enforce that afterwards.
For the spatial part, the same category is permit-free under Article 2.29(c) Bbl, provided the following dimensions are met:
- In the rear roof slope, a side roof slope that does not face publicly accessible land, or a flat roof: the structure projects no more than 0.6 metres beyond the roof slope or flat roof, and the sides, bottom and top are more than 0.5 metres from the edges of the roof slope or flat roof.
- In any other roof slope, such as the front roof slope or a side roof slope facing the street: the structure does not project beyond the roof slope, and the sides, bottom and top are more than 0.5 metres from the edges of the roof slope.
That is an important difference from a dormer: a roof window can also be permit-free at the front, as long as it stays within the roof slope and is everywhere more than half a metre from the ridge, the eaves and the sides of the roof slope. An ordinary roof window that lies roughly in the plane of the tiles usually fits within that in practice; a rooflight or upstand that clearly projects above the roof slope does not. The law does not specify a permitted number of centimetres; if in doubt, ask the municipality. According to the Informatiepunt Leefomgeving (IPLO, the government information point for the living environment), this national rule always takes precedence over the local rules in the omgevingsplan (environmental plan); the municipality can, however, designate additional permit-free cases.
If the window does not meet these dimensions, for example because it comes too close to the ridge or the gutter, you need an omgevingsvergunning (environmental permit) for the environmental plan activity. The municipality then assesses it against the environmental plan and, if your municipality has them, against welstand (design and appearance) criteria.
Exceptions: listed building, protected view and illegal construction
- Listed building. On a municipal, provincial or national monument (listed building), including one under provisional protection, only ordinary maintenance falls under Article 2.29 (Article 2.30(1) Bbl). A new roof window then always requires a permit. For a rijksmonument (national monument), a permit for the national monument activity is also required; the only thing permit-free there is necessary regular maintenance aimed at preserving the monumental values, without changing, among other things, detailing, type of material and colour (Article 13.11 of the Besluit activiteiten leefomgeving, the Dutch Activities Decree). Adding a roof window does not fall under that.
- Nationally protected townscape or village view. If your location has the designation rijksbeschermd stads- of dorpsgezicht (nationally protected townscape or village view) in the environmental plan, a roof window remains permit-free only in a rear roof slope that does not face publicly accessible land (Article 2.30(3) Bbl). In the front roof slope, in a side roof slope or in a rear roof slope that overlooks a street, path or public green space, you then need a permit.
- Illegally built structure. The exemptions do not apply to a structure that was built or is used without the required environmental permit or completion notification (Article 2.22 Bbl). A roof window in an extension or attic extension that was put up without a permit at the time is therefore not automatically permit-free.
The only way to get certainty for your address is the vergunningcheck (permit check) in the Omgevingsloket (the national environment and planning portal) at omgevingswet.overheid.nl. Enter the address, the roof slope and the dimensions and keep the outcome, even if it says permit-free. An overview of permits for other renovations can be found in When do you need a permit for a renovation.
Flats and neighbours
If you live in a flat on the top floor, the roof is as a rule a common part of the building. A roof window is then an alteration to something that is not yours alone, and for that you need permission from the owners' meeting under the splitsingsreglement (deed of division rules). Arrange this before you hire a tradesperson; the municipality does not check whether the VvE has agreed. For more, read Renovating a flat in a VvE.
A roof window in a pitched roof usually looks mainly at the sky. If it sits low in the roof, close to the property boundary, and you can use it to look straight into the neighbours' property, the neighbour law on windows within two metres of the property boundary (Article 5:50 of the Burgerlijk Wetboek, the Dutch Civil Code) may come into play. Inform the neighbours in advance in any case, especially if scaffolding or a roof ladder has to go on or along their property. More on this in Renovating and the neighbours.
Structure: rafters, purlins and trimming
A roof window seems a small job, but the carpenter is cutting a hole in the roof structure. How that is done depends on how your roof is built.
- Rafter roof. The roof boarding rests on sloping beams, the rafters, which run from the gutter to the ridge. If the window fits between two rafters, no rafter needs to be removed. If the window is wider, a rafter is interrupted and supported with a trimming structure (raveel): cross beams above and below the opening that transfer the load to the adjacent rafters.
- Purlin roof. Many homes have horizontal purlins between the party walls, with roof boards or roof panels on top. The carpenter then cuts an opening in the roof panel and reinforces the edges with trimmers. A professional will not simply saw through a purlin; usually the window is positioned so that it falls between two purlins, or a structural engineer is brought in first.
The Bbl requires the structure to remain safe after the renovation. With a large window, several windows side by side, an old roof with heavy tiles or doubts about the condition of the timber, a structural assessment is sensible. A good carpenter also checks beforehand for wood rot, signs of leaks and, in homes built before 1994, for materials that may contain asbestos.
Building in watertight: flashing, tiles and interior finishing
Most roof window leaks do not originate in the window itself, but in the connection to the roof. That is why building it in revolves around a few components:
- Flashing. Around the frame goes a flashing kit (gootstuk), also called a connection set, which guides the water around the window to the tiles below. There are different flashing kits for profiled tiles, flat tiles and slates; it must suit your roof covering and be fitted according to the manufacturer's instructions.
- Connection to the tiles. Tiles beside and above the window are shortened or relaid so that there is room for water drainage. At the bottom, a pliable strip lies over the tiles and adapts to their profile.
- Underlay. If there is a water-resistant, vapour-permeable membrane under the tiles, it must connect neatly to the frame, with a drainage gutter above the window so that water that lands on the membrane is guided around the opening.
- Insulation and vapour control. On the inside, there should be insulation around the frame and a vapour-retarding connection to the interior finish. If that is missing, warm, moist indoor air can condense in the structure, which later feels like a leak.
- Lining. The interior finish with plasterboard, sheet material or plaster completes the job. A frequently given piece of advice is to finish the top of the reveal horizontally and the bottom vertically, so that warm air can flow along the glass. If you have the plastering done separately, you bring in a plasterer.
If you replace an existing roof window, under Article 5.20(2) Bbl the new window, including its frame, must have a thermal transmittance (U-value) of no more than 2.2 W/m²·K, or the old level if the existing window already insulated better. Whether the same requirement also applies to an extra roof window in a place where there was no window before is not expressly regulated by the Bbl; in practice, treat 2.2 as a maximum (a lower U-value insulates better) and have the U-value of the whole window stated in the quote. Modern roof windows with insulating glass usually stay well below that value.
The roof window leaks: finding the cause
Water at the roof window does not always mean a leak. First look at when it gets wet: only when it rains, or rather when it is cold without rain?
- Condensation rather than a leak. Drops at the bottom of the window or along the lining in cold, dry weather are usually condensation. In that case ventilating helps more than a roofer.
- Flashing or connection. An incorrectly fitted, damaged or wind-loosened flashing kit, or displaced tiles beside the window, let water through in rain and wind.
- Dirt and leaves. Leaves, moss and dirt in the flashing above the window can make the water back up until it runs over the edge.
- Window seals. Worn rubber seals, a window that does not close properly or a ventilation flap left open let water in during driving rain.
- Leak higher up the roof. Water that comes in at the ridge or through broken tiles sometimes runs down along the underlay and only comes inside at the roof window opening.
For the outside, such as flashing and tiles, call a roofer; for the window, the seals and the interior finish, a carpenter. If you are unsure which tradesperson you need, read Leaks: which tradesperson should you call? In the meantime, take photos of the damp patch and the conditions, so that the tradesperson can search more efficiently.
Condensation on the roof window
A roof window is sloped and catches the cold night air, so the inside of the glass gets cold faster than with a vertical window. In an attic bedroom, where a lot of moisture is released at night, that moisture settles on the coldest surface. Keep the ventilation flap open, make sure the rest of the house is well ventilated and have the interior finish done so that warm air can reach the glass. Condensation between the panes indicates a faulty insulating glass unit; that must be replaced. Light condensation on the outside of well-insulating glass on cool mornings is actually a sign that the glass lets little heat through. If you also have damp or mould elsewhere, Recognising damp and mould in your home helps you find the cause.
Sun protection and roller shutters
An attic with roof windows can heat up considerably in summer, because the sun shines on them high and directly. Sun protection on the outside, such as an awning blind or roller shutter, stops the sun's heat before it reaches the glass and therefore works better against heat than a roller blind or blackout blind on the inside. According to Milieu Centraal (the Dutch environmental information centre), sun protection on the outside works at least twice as well as on the inside. Interior blinds are mainly useful for blacking out or limiting the view in. Most sun protection is made for a specific type and size of roof window; the data plate on the window tells you which version fits. An electric roller shutter or blind needs a power connection or a solar cell.
Who does the work and what goes in the quote?
Fitting a roof window in a pitched tiled roof is typically work for a carpenter: they make the opening and the trimming structure, fit the window and the flashing and finish the inside. Many carpenters also make the connection to the tiles themselves; for a tricky connection, a slate roof or a rooflight in a flat roof with bitumen or EPDM, a roofer is brought in. For an electric window or roller shutter you need an electrician. A standard roof window in a simple roof is often fitted in a day, with the interior finish as a separate step.
Request several quotes and make sure they record at least:
- the brand, type, size and operation of the window, the type of glass and the U-value;
- which flashing kit is used and whether it suits your roof covering;
- whether the trimming structure, insulation around the frame and the vapour-retarding connection are included;
- how the interior finish will be done and whether plastering and painting are included;
- scaffolding or roof ladder, removal of waste and restoring tiles;
- who does the permit check and, if necessary, applies for the permit;
- sun protection, electrical connection and any extra windows;
- the guarantee on the watertight connection alongside the manufacturer's guarantee on the window.
How to compare quotes side by side is covered in Comparing quotes: how to read a building quote.
VAT on a roof window: 21 per cent
For homes more than two years old, the low VAT rate of 9 per cent applies only to a limited list of work, such as painting, plastering, wallpapering and installing insulation material, and for insulation only to the labour. Fitting a roof window is not on that list, and according to the Belastingdienst (Dutch Tax Administration) window frames do not count as insulation material. So you pay 21% VAT on the window and on fitting it. Sun protection is also charged at 21 per cent. If plastering is done on the inside as part of the same job, that part may fall under the low rate. The details are in 9% or 21% VAT on renovations.
In summary: a roof window or rooflight is permit-free nationally, including in the front roof slope, as long as it does not project beyond the roof slope there and is everywhere more than half a metre from the edges; at the rear and on a flat roof it may project up to 0.6 metres. For a listed building you always need a permit, and in a nationally protected townscape or village view the exemption only remains in a rear roof slope that does not face public land. Do the permit check, sort out the VvE, and have the window fitted by a professional who carries out the structure, the flashing and the interior finish properly. On VerbouwPro you post your job free of charge, and carpenters and roofers from your region respond.