Can a flat rooflight go over a shower?

Laminated glass over a person standing in bare feet

Any rooflight has a toughened outer pane and, in a good specification, a laminated inner. Over a shower tray the laminated inner stops being a recommendation and becomes the reason the unit is acceptable at all.

Toughened glass breaks into small blunt granules rather than shards, which is the right behaviour for the outer pane. It is the wrong behaviour on its own overhead, because those granules fall. A laminated inner pane, typically 6.8mm or 8.8mm with a polyvinyl butyral interlayer between two plies, holds the broken glass to the interlayer and keeps it in the frame. The specification to ask for is toughened outer, laminated inner, and it applies over a bath, a shower, a stairwell and a bed alike.

There is a second reason it matters in a bathroom specifically. Sudden temperature change across a pane is greatest where a hot shower runs under cold glass on a February morning, and while a properly heat soaked toughened pane copes with that, the laminate is the layer that decides what happens if it does not.

Steam behaves differently from cooking moisture, and it arrives faster

A shower puts a large amount of water vapour into a small room in about eight minutes. A kitchen releases a similar total over an hour or more with a hob extract already running. The rooflight is the coldest surface in a bathroom by a wide margin, so it is where that vapour lands first, and it will run with water on the room side within a minute of the shower starting.

That is condensation doing exactly what physics says it should, and it is not a fault in the unit. What decides whether it becomes a problem is where the water goes next. A modern flat rooflight frame has a drainage channel around the inside of the glass with weep holes taking it out to the roof surface, and on a bathroom unit that channel does real work every single day. It is left clear on installation and it is never sealed over with mastic. The wider physics of condensation on flat glass sits on the flat rooflight condensation page.

Extract fans, opening units, and which one the room actually needs

Building Regulations guidance sets intermittent extract in a bathroom at 15 litres per second, and that requirement exists whether or not there is glass in the roof. A fixed rooflight contributes nothing to it. Where the room already has a fan on the wall or in the ceiling, a fixed pane is fine and the fan carries on doing its job.

Where the room has no fan, or where the fan is a token one from a 1990s refit, an opening rooflight is worth considering as part of the same visit. An electrically actuated flat unit with a rain sensor clears a steamed bathroom faster than any domestic extract fan, because it moves a large volume through a large aperture rather than a small volume through a 100mm duct. It also solves the problem of a fan duct that has to cross a warm deck. Wiring, controls and sensors are covered under electric rooflight installation, and the operating options generally on can a flat rooflight be opened.

Shower zones, IP ratings and where a motor is allowed to live

The wiring regulations divide a bathroom into zones measured from the bath or the shower tray. Zone 1 is the space directly above the tray up to 2.25 metres from the floor. Above that height, in a room with a normal ceiling, the space is generally outside the zones, which is why a ceiling mounted actuator in a single-storey extension with a 2.4 metre ceiling is usually straightforward.

Usually is not always. A shower under a low ceiling, or a unit set in a deep reveal that brings the frame down towards 2.25 metres, changes the answer. The practical route is an actuator with an appropriate IP rating, supplementary bonding and RCD protection, positioned with the zone boundaries measured rather than estimated, and the electrical work notified under the electrical part of the regulations along with the rest of the job.

Overlooking from an upstairs window next door

People assume a roof is private. In a terrace or a tight semi it frequently is not, because the neighbour’s rear bedroom window looks straight down onto a single-storey rear addition roof. Before specifying clear glass over a shower, it is worth standing at that window, or looking at the elevation from the garden, and working out who can see in.

The options are ordinary. An obscure or acid-etched inner pane gives full privacy and still passes plenty of daylight, at the cost of the sky view. A body-tinted or heavily reflective outer reduces daytime visibility from above but reverses after dark when the bathroom light is on. An integral blind between the panes, or a blind fitted to the frame, gives control rather than a permanent decision. On balance, an etched inner pane is the specification that causes the fewest regrets in a shower room.

Reaching the glass in a room where it will be cleaned often

Bathroom glass gets a film on it that kitchen glass does not: soap aerosol and shampoo carry into the air with the steam and settle on the coldest surface. On the inner face of a rooflight that builds into a haze within a year if nothing is done about it.

So reach is worth thinking about before the unit is positioned. In a single-storey extension with a 2.4 metre ceiling and a 300mm reveal, the inside of the glass is at roughly 2.7 metres, which is a step ladder job and perfectly manageable. Put the same unit over a bath and the ladder has nowhere level to stand. Where the bath is fixed and the rooflight has to go over it, an opening unit that rotates or lifts far enough to reach the inner face is worth the money it adds.

Ground floor shower rooms in Gloucester rear additions

A recurring job through Tredworth, Barton, Longford and the Victorian terraces of the city: a Victorian outrigger converted into a downstairs shower room, one small window onto a side alley that nobody wants to open, and a flat roof over the top. That flat roof is very often a 1970s felt deck with a crazed plastic dome in the middle of it.

Swapping that dome for a glass unit on a properly built and insulated kerb changes two things at once. The daylight is transformed in a room that has had almost none, and the cold ring of bare timber that the old kerb was, which is where the black spotting in the corner of the ceiling came from, is replaced with insulation carried continuously around the outside of the new kerb. The vapour control layer is taped to the frame rather than trimmed short of it, which matters more in a bathroom than anywhere else in the house.

What gets checked before a bathroom rooflight is ordered

At survey the specific bathroom items are the deck build-up and its condition, the joist direction and the clear width between them, the ceiling height and the depth the reveal will add, the position of the shower tray relative to the proposed opening, the existing extract provision and whether it is working, the route for any cable, and who can see in from where. Glass specification follows from that: laminated inner as standard, obscure where overlooking is real, solar control where the roof faces open sky.

Then the usual sequence. An indicative range by email from photographs of the roof and the room, then a survey, then a fixed price with the Building Control notification submitted and closed out as part of the job. The costs page sets out how that works, and the written guides go further into individual questions.