Is a flat rooflight a good idea in a bathroom?

Most bathrooms are small, tucked in the middle of the plan, and fitted out to the walls. A rooflight solves the problems that come with that.

A bathroom in an extension or a converted loft often has an outside wall that is wanted for the bath or the basin run. A rooflight leaves that wall alone. The daylight arrives from above, falls evenly down the tiles and reaches the corner of the shower. It is gentler than a bright window at eye level, and it does not throw a hard patch across the floor the way a low sun through a side window does.

It also lets a bathroom exist where a window cannot. An internal room under a flat roof, such as an ensuite behind a bedroom, can have real daylight instead of a lamp and a fan. That is common in Crawley's 1950s to 1970s homes, where a single storey flat-roofed addition sits behind the main house and the new bathroom has no outside wall to spare.

There is a quiet benefit too. A bathroom is a room you use early and late, so the rooflight should keep the sound of the weather out as well. The glass build we specify for the room is set out in our page on quieter glazing for a flat roof rooflight over a bedroom, and the same build works well over a bathroom.

A bathroom makes more moisture than any other room, and a rooflight is usually its coldest surface. Planning for that is what keeps the ceiling clean.

Steam rises, meets the coolest surface it can reach and turns to water. On a poor unit that surface is the glass and its edge, which is why old single-skin domes run with condensation. A sealed double-glazed unit with a warm edge spacer keeps the inner pane and its edge closer to room temperature, so far less water collects there. The edge detail matters as much as the pane, and our page on a flat rooflight in a warm or cold roof explains where the cold spots are around the opening.

Glass cannot do the whole job, so extraction is part of the design:

1. A fan sized for the room. Building Regulations Part F asks for mechanical extract in a bathroom, with a rate set in the approved document for the room type. A fan that runs on after you leave clears the last of the steam.
2. A ducted route out. The duct should run to the outside, with a fall away from the fan, so condensation in the pipe does not run back down.
3. An opening unit where it helps. A rooflight that opens, by hand or by motor, adds ventilation on top of the fan. Our electric and opening rooflight installation page covers those.

Where the rooflight opens, the motor and controls in a wet room have to be rated for it. That is checked when the model is chosen, and sits alongside the room's electrical zones, which a qualified electrician sets out.

Overhead glass is hard to see into from the ground, but upstairs windows next door can look down at it. The finish of the glass decides whether that matters.

A flat rooflight sits above eye level, so anyone at street or garden level sees only sky. The exception is a taller building nearby, such as a two-storey house overlooking a rear extension, where the glass can be seen from a bedroom window. That is the case for privacy glass, and there are three sensible routes:

Obscured glass loses a little light, but a bathroom rarely needs full brightness and the soft tone is pleasant. We set out the choices in can a flat rooflight have obscure glass for privacy. A blind under the glass is another route, and fitting a blind to a flat rooflight explains what works in a damp room.

A bathroom rooflight is overhead glass above a wet floor, so it is specified as safe to fall under.

Part K covers safety glazing, and overhead, good practice is a laminated inner pane, so that, if it ever cracked, the glass holds together instead of dropping. That is our standard build for flat rooflights. The outer pane is usually toughened. Our page on what glass a flat rooflight should have sets out why the pairing works.

Structure and roof are the same as any other room. The opening needs an upstand, the joists may need trimming, and the membrane is dressed up to the kerb. A bathroom adds one detail: the vapour layer under the ceiling should be continuous and sealed to the reveal, because this is the room that sends most moisture upward. We install to current Building Regulations and handle the Building Control notification where the work is notifiable.

Because a bathroom is small, a rooflight of modest size usually does the job. Our page on what size flat rooflight suits an extension gives the method for working out the glass area, and a bathroom sits at the small end of it.

Will a rooflight make the bathroom cold?

Not with a modern sealed unit. A coated, gas-filled, warm edge double unit loses far less heat than older glazing. Good lining and an insulated upstand finish the job, and our energy efficient rooflights page covers the wider picture.

Can I put a rooflight over the shower?

Yes. The glass is not affected by the water, and the sealed unit is built for damp rooms. The concern is any fitting, such as a motor or light, which needs the right rating for the zone. We choose the model with that in mind.

Does the glass need cleaning more often in a bathroom?

Steam carries soap film and minerals, so the inside may need an occasional wipe. The outside is cleaned like any rooflight, as set out in how to clean a flat rooflight.

When you are ready to plan a bathroom rooflight, get a quote and the glass, extraction and finish are written into the quiet spec. The full service is on our flat roof rooflight installation page.