Can a flat rooflight go over a shower?

Condensation

Directly above a shower is the wettest air in the building meeting the coldest surface in the room. Every part of the detailing matters more here.

A warm edge spacer so the glass perimeter is not the coldest point. An insulated kerb so the upstand is not a cold bridge. And the vapour control layer sealed to the frame so wet air cannot get into the roof build up.

Skimp on any of those over a shower and it will show in the first winter.

Ventilation

Mechanical extraction is required regardless. An opening rooflight helps a great deal on top of it, because it removes the wettest air at the highest point of the room, but it does not replace the fan.

Over a shower the unit is above reach, so electric with a rain sensor is the version that gets used.

Electrical zoning

If the rooflight is electric and sits over or near the shower, it falls within the bathroom zones and the unit and its wiring must be specified accordingly.

That is an electrician’s decision and it belongs in the specification from the start rather than being discovered at second fix.

Privacy

Usually a non-issue on a single storey extension. Where there is an overlooking upper window, obscured or acid etched glass solves it without losing daylight and costs little.

Cleaning

Steam carries soap and shampoo residue upward, and it lands on the glass. Expect the inside face to need cleaning more often than a rooflight elsewhere.

Yes, and three things need thinking about

A rooflight over a shower is a good idea. Bathrooms are frequently the darkest rooms in a house and a shower enclosure is the darkest part of the bathroom.

What changes is that you are putting glazing directly above the wettest, steamiest point in the building, and that has consequences for condensation, privacy and access.

1. Condensation

Steam rises and meets the coldest surface in the room, which after you fit a rooflight is quite likely to be the rooflight. Water then runs off it, and from inside a shower that looks like a leak.

Three things address it. A good whole unit U-value and a warm edge spacer, so the glass runs warmer. A properly detailed and insulated kerb, so the perimeter is not a cold bridge. And genuine extract ventilation, which matters most of all.

An extract fan sized for the room, running on an over run timer or humidity sensor, and ducted to outside rather than into a loft, is what actually keeps a shower room dry. A rooflight does not ventilate unless it opens, and even then it is not a substitute for a fan.

2. Privacy

A rooflight faces the sky, so overlooking is rarely an issue except where the property sits below higher ground or another building looks down onto the slope.

Where it is a concern, obscure glazing solves it permanently without a blind, and it costs a modest premium at the point of order. In a shower, where a blind would get wet, that is usually the better answer.

On a side elevation facing a boundary, permitted development may require obscure glazing anyway.

3. Access and cleaning

Think about how the glass gets cleaned from inside before it goes in. Standing in a shower tray on a stepladder is not a good arrangement.

Where the unit opens, a centre pivot design that rotates for cleaning is worth considering, or a pole system. Self cleaning glass helps on the outside.

Should it open

Usually yes. An opening at the highest point of a shower room lets steam leave directly rather than circulating, which is the fastest way to clear a room.

Above reach, that means motorised, and a rain sensor matters because a bathroom rooflight left open in a shower is a wet floor. On a retrofit into a finished bathroom, solar avoids running cable through a tiled wall.

Electrical zones

Worth mentioning: bathrooms have defined electrical zones and equipment near a shower has to be rated accordingly. A motorised rooflight above a shower is a case where the electrician needs to know exactly where it sits, and that is settled at design stage rather than on the day.

Yes, and it is a good idea

A shower is the wettest, most humid point in the house and frequently the least naturally lit, because privacy has pushed the glazing away.

A rooflight above it gives daylight with no overlooking at all, and puts ventilation at the highest point in the room, which is exactly where the steam collects.

The condensation problem, which must be designed for

A shower produces a great deal of water vapour very quickly, and it rises straight to the ceiling. The rooflight is the coldest surface up there, so it collects that moisture first and it will drip if the detailing is poor.

Three things prevent it.

A good whole unit U value with a warm edge spacer, so the internal surface is warm enough not to condense readily.

An insulated kerb, continuous with the roof insulation. An uninsulated kerb over a shower will run with water every time it is used.

A vapour control layer sealed to the frame, so humid air cannot get into the construction and condense out of sight, where it rots timber silently.

Extraction alongside the rooflight

An openable rooflight helps enormously, but it does not remove the requirement for mechanical extraction where the regulations call for it. The two work together: the extract handles the shower itself, the rooflight handles the rest.

Where the unit is powered and out of reach, a rain sensor is essential, because an open rooflight over a bathroom in a shower of the other kind is a poor combination.

Specification detail

Choose a moisture resistant finish rather than painted timber, and a blind that tolerates humidity if one is wanted at all.