The short answer
Yes. A roof window works well in a bathroom, because it brings in daylight and lets steam escape, as long as the frame is made for damp rooms. Choose a moisture-resistant finish, place the window away from the shower spray where you can, and add extraction so condensation does not build up on the glass and the lining.
What suits a damp room, where to put the window, and how to keep condensation and mould under control in a bathroom.
Why bathrooms need a different frame
A bathroom is the wettest room in the house, and a roof window sits in the coolest, dampest spot in it, the sloping ceiling. Warm steam rises, meets the cold glass and turns back into water. A frame that is made to cope with that will last, while one that is not can swell, flake or darken.
Makers offer frames for wet rooms. Typically these are finished in polyurethane, or in something that shrugs off water, rather than bare pine under clear lacquer. Ask the supplier which finish suits a bathroom, and check that the sash is double glazed with a seal that copes with steam. The sheet for your model lists the frame material and how it is treated.
The inner lining, the panels that fill the space from frame to ceiling, needs to be moisture-resistant as well. Plain emulsion on bare plasterboard will mark quickly in a steamy room. A mould-resistant paint or a tiled reveal copes better, and a wipe-clean finish makes cleaning the lining easy. Our answer on condensation on a Velux window covers what the water on the glass is telling you.
Where to put the window
Position decides how often the window mists up. Over the bath or shower the glass takes the full blast of steam, and that is the place most likely to run with water. Setting the window to one side, or above the basin or the toilet, spreads the load. Where the layout leaves no choice, a window with an opening sash that you can crack open after a shower helps the air move.
Height matters for privacy and for reaching the handle. A window in a sloping ceiling over a stair or a bath can be awkward to open by hand, and a pole or an electric opener makes it easier.
Privacy is simpler than people expect. From the ground, a roof window usually looks up at the sky, but a neighbouring higher building may see in. Frosted or obscure glass, or a blind that drops from the top, fixes that. A window on a side-facing slope has to be obscure-glazed anyway under Class C of the General Permitted Development Order.
Controlling condensation and mould
Even the best frame cannot beat a room with no ventilation. BS 5250 covers moisture control in buildings, and the idea behind it is to stop the steam you make settling inside the structure. For a bathroom, that means an extractor fan that actually vents outside, run during the shower and for a while afterwards, and a gap under the door so replacement air can come in.
The window helps by letting you air the room, but it does not replace a fan. If the glass is dripping every morning, look at the fan first. A fan that vents into the loft only moves the problem to the roof timbers, so the duct should run to the outside.
Keep the area around the window clean. Wipe the glass and the sill after a bath, and treat any speckled black spots on the lining straight away with a suitable mould remover. Check the sealant around the frame for gaps as well. If there is water on the lining after rain rather than after a shower, the fault is outside, and our page on why a Velux window leaks will help.
Fitting a new window into a bathroom ceiling
If you do not have a roof window yet, fitting one into a bathroom ceiling follows the same steps as any other room, with a few extras. The opening is cut between the rafters, the frame is fixed, and the flashing seals it into the roof covering. Inside, the lining has to be finished in a damp-room material and the pipes, cables and fan duct kept clear of the opening.
Check whether the opening can sit where you want it. If a soil pipe, a water tank or a chimney is in the way, the position may have to shift. The size of the window should suit the room, as a large pane over a small shower room can feel exposed and may leak heat in winter.
Building control may need notice for a new opening in a roof, and a replacement roof window has to meet the window value in Approved Document L, which is currently 1.4 or Window Energy Rating Band B under the 2021 edition. Our cost to fit a Velux window page gives national prices, and the roof windows and skylights hub shows how we work. Send us the bathroom layout and a photo of the ceiling, and tell us where the shower, bath and basin sit, and we can say where a window would work best and what the lining should be made of.
More on this in Velux Roof Windows & Skylights in Crawley
Two bathroom questions
Will a roof window in a bathroom steam up?
It can, because warm moist air meets cold glass. How badly depends on the glazing, the fan and the position. A sealed double-glazed unit, a working extractor and a window set away from the shower all cut the amount. A little mist after a hot shower is normal, and it should clear soon after.
Do I need special glass in a bathroom?
Not for moisture, but obscure glass gives privacy when a neighbouring building overlooks the roof. For a window on a side slope, obscure glazing is a Class C requirement in any room. A blind that closes from the top is another route if you want clear glass in the daytime.