What Is a Skylight Light Well?

When a roof window sits in a loft that has a ceiling below it, there is a gap between the glass in the roof and the plasterboard in the room. That gap is boxed in with four sides, forming a tunnel for the light. The tunnel is the light well, and its inner faces are the reveal. You see the end of it as a framed opening in the ceiling.

Light wells are needed where the roof is deeper than a ceiling, which is common over a landing, a stair or a top-floor room with a loft above it. The roof window might be a metre or more above the ceiling, and the well has to carry daylight down through that space without losing it on the way.

The structure around the well is built from timber studs, fixed between the roof rafters and the ceiling joists. These are boarded with plasterboard, skimmed or decorated, and lined behind with insulation. Done well, you notice a clean opening in the ceiling and a bright room. Done badly, you get a dark box and a cold patch where steam and warm air condense. Our answer on stopping a skylight overheating looks at the other side of light control.

A straight well has parallel sides, so the opening in the ceiling is the same size as the window above. Light falls straight down and lights a patch of floor, but the walls of the well absorb some of it on the way. A splayed well is wider at the ceiling than at the roof, so its sides slope outwards and bounce light into the room.

Splaying turns the reveal into a reflector. Painted white or a pale colour, it spreads daylight across the ceiling and the walls, and the room feels brighter even though the glass has not changed. The wider the splay, the more light reaches the corners, within what the structure allows. A well that is splayed on the lower sides only, with the top kept near vertical, suits a room where the glare of the sun is a problem.

The trade-off is space. A splayed reveal takes up more ceiling, and the joist layout has to allow for it. A straight well is simpler to frame and cheaper to finish, and works well when the shaft is short. When the gap between roof and ceiling is large, the splayed form usually earns its extra work. We help you choose by looking at the loft side and the room below.

The well passes through the loft, which is cold, so its walls must be insulated. Without insulation, warm moist air from the room meets cold plasterboard and condenses, leaving damp patches and mould near the opening. Fitting insulation around the whole shaft, and sealing the joints, reduces that risk. The window itself must also suit its position, and replacement rooflights have to meet the value in Approved Document L, which is 2.2 in the 2021 edition for new or replacement rooflights.

The lining needs a smooth, bright finish. White matt paint reflects most light. Gloss shows every ripple in the board, so it is best avoided. Check the sealing between the window frame and the top of the well as well, because a gap there lets cold air in and creates drips in cold weather.

Fire matters if you plan a loft conversion. A well that runs through a protected stairway or a fire-resisting ceiling may have to keep that resistance, so ask building control before the framing starts. Our answer on Building Regulations for roof windows explains what they look at, and the roof windows and skylights page shows the full range of what we fit.

A light well is lined with plasterboard and lets in a view of the sky through a normal roof window. A sun tunnel is a different product: a little domed collector on the slope, linked through the loft by a mirrored tube to a diffuser panel in the ceiling. It brings light but no view and no ventilation, and it suits small dark spaces such as a hall or a bathroom with little room to spare. Our answer on sun tunnel cost covers what drives that price.

Choose a well when you want the view, the opening sash and a wide spread of light, and when the roof structure above the ceiling is deep enough to allow the shape. Choose a tube when the route is long and twisting, or the room is too small for a window.

Whichever you pick, the written quote from us follows a survey, and covers the roof opening, the well, the lining and the redecoration needed. Send us a photo of the ceiling and a note of how far it is from the roof slope. If you can reach the loft, a photo of the space above shows whether there is room to splay the sides.