Skylights and rooflights across Kingswood, Bristol

Does a bathroom rooflight need to open? Over a room with a flat or low-pitched roof it is worth thinking about, because a fixed pane lets light in and leaves the steam where it is. An opening unit gives warm air a way out and lets the glass clear after a shower. The ceiling above a bath is also out of reach, which is where an electric opener comes in.

An electric rooflight opens at the touch of a wall switch or from a handset. According to VELUX, its electric and solar roof windows carry a built-in rain sensor that shuts them once rain starts, and that sensor is particular to those models. VELUX also makes solar roof windows, and which route suits depends on the position of the roof and what lies beneath it. The comparison of electric and manual opening sets out the choice.

Power is the practical side. An electric unit needs a feed to the opening, and the cable route is something the survey works out. A bathroom is also a place where water and electricity sit close together, so the position of the switch gets thought about before anything is ordered.

Late in the day the glass above the bath behaves like a dark mirror. With the bathroom lit and the sky beyond it black, the pane returns the room to itself, and anyone looking from a window higher up can see in. A blind drawn across solves that. The same steam that clouds a mirror gathers on cold glass, so letting the room air while the shower runs is a habit worth having.

If the bathroom roof is pitched, a roof window is the product and the choice is again between an electric, solar or manual opener. Our roof windows hub shows how they differ.

A last point is the blind. A rooflight over a bathroom can take one, and a bathroom blind is something to choose for the room's damp air as much as for the light. Ask about it when the opening unit is chosen, so both arrive together.

Think about the hours a family room is used. In November most of them come after dark, so a lantern earns its place at weekends and at midday, and in the evening it shows a lit room in dark glass. It does not produce any light. What you see in it is the table, the pendants and the kitchen behind you.

Structurally, a lantern is a raised glazed frame set on an upstand, and its glazing is pitched. It is a bigger structure than a flat rooflight, and the structure beneath it is part of the survey. The comparison of lantern against flat rooflight weighs the two for a given room.

Planning needs a look. Over an old flat roof a lantern generally stands well clear of the surface, which normally puts it outside Class C and makes permission the starting point unless the council says otherwise. Our English planning section gives the background. Should the lantern be part of a new extension, South Gloucestershire Council is asked about it before work begins.

Heat is the other thing to weigh. A lantern has a lot of glass, and a cold evening makes the table feel it. A blind inside the glass, or glass with a good rating, can take the edge off. The page on energy-efficient rooflights explains how the ratings are set.

Looking up from the table at supper, you see the frame. Its colour and its bars are in view every evening, so they are worth choosing with the kitchen in mind. A pale ceiling lining throws the room's own light back, and a dark one lets the glass fade out of sight.

Last, think about the ceiling the lantern opens. The joists around the opening are usually trimmed and carried to either side, so the size of the glass is limited by the timbers. The survey measures that before a size is chosen, and a lantern for a new extension can have the opening framed in from the start.