What is a splayed rooflight lining?

Daylight comes through a rooflight from many angles across the day, not straight down. In a straight lining, much of that light strikes the sides of the shaft at a shallow angle, and the faces furthest from the sun stay dull. The room gets a bright patch on the floor under the glass and a dim frame around it.

Angle those faces and two things change. The opening at the ceiling is bigger, so more of the room has a direct line to the glass. And the splayed surfaces face the room rather than each other, so the daylight they pick up is reflected outwards instead of back and forth inside the shaft. A white or pale finish on the splay helps further. The rooflight itself is unchanged: same frame size, same glazing, same position on the roof.

The gain is most noticeable in winter and on dull days. In December the sun stays low over Devon even at midday, so its light comes in at a low angle and much of it strikes the faces of the lining before it reaches the room. On an overcast day, daylight arrives from the whole sky at once, and a wider opening simply takes in more of it.

There is also a visual effect that matters as much as the light. A splayed reveal reads as a designed opening, the way a deep window reveal does in a thick stone wall. A straight one through a deep roof can look like a loft hatch with glass in it.

The deeper the gap between frame and ceiling, the more a splay gives back. The clearest case is a flat ceiling under a pitched roof, where the rooflight sits on the slope and a shaft drops through the cold loft to the room. Landings, hallways and stairwells in older houses are typical, and so are bathrooms in 1930s semis where the only daylight has to come down through the loft.

A splay is also worth considering when:

• the rooflight is small relative to the room, and you want the opening to look generous;
• the roof build is deep, with thick insulation, as in many recent loft conversions and new builds;
• the room has a high ceiling and the opening would otherwise look like a slot;
• the glass faces north and you want to make the most of the softer daylight it gets.

In a period house with lath and plaster ceilings, the splay can also be a way of making the new opening sit naturally in the room. Georgian rooms in St Leonards or Southernhay already have splayed window reveals in their walls, and a rooflight finished the same way looks as if it belongs.

Under a sloping loft ceiling, the lining may be only 150 to 250mm deep. Splaying a reveal that short widens the ceiling opening by very little, and it adds finishing work for almost no gain. A neat straight lining, square to the glass with crisp edges, is usually the better finish there.

A straight lining also makes sense when space around the opening is tight. A splay needs room to fan out, and if a ceiling joist, a purlin, a wall or a light fitting sits close beside the frame, there may be nowhere for it to go. In a run of roof windows set side by side, the gaps between frames are often too narrow to splay the inner faces, although the head and sill can still be angled.

Some people simply prefer the look of a straight reveal in a modern, angular room. That is a fair choice, as long as it is made knowing the alternative rather than ending up as the default because nobody raised it.

A splayed lining is more work than a straight one, and it is fair to know where the extra time goes.

The ceiling opening is larger, so in a flat ceiling the joists may need trimming as well as the rafters above. That is a structural alteration in its own right, and it is covered by the same Building Control notification as the rest of the rooflight work. The lining frame is built to the angles rather than square, and the insulation behind it has to follow those angles closely, since a gap behind a splay is a cold spot that shows as damp staining later.

The corners change too. Where a splayed side meets the ceiling, the angle is wider than a right angle, so standard angle bead won't sit flat. A flexible or adjustable bead is used so the arris stays sharp. Plastering four faces at different angles takes more care than four square ones, and in an old house with lime ceilings, each face may be built up in several coats. None of this changes the rooflight you order, but it does change the day or so of finishing that follows the fitting.

For the full sequence, from insulation and boarding to beads and paint, see our guide to how a rooflight is finished inside.

Many quotes for a skylight say nothing about the lining at all, which usually means a straight box. If you want a splayed skylight reveal, ask for it to be written into the quote with the angles or the ceiling opening size, so there is no doubt on the day.

Every Brightview quote comes with a finish schedule that records how deep the lining runs, whether it will be straight or splayed and why, and how it will be finished. If the roof is shallow and a splay won't help, the schedule says that too. For loft rooms, our page on roof window installation covers how windows are placed between rafters, which affects how much room a splay has.

When you're ready, ask for a quote and we'll look at the depth of your roof and ceiling before recommending either.