The short answer
Replacing a skylight disturbs the plaster around the opening, but it should not damage the ceiling as a whole. The reveal, the lining that runs from the ceiling up to the glass, is the part that is the part touched most. On a like for like swap it is usually left alone or given a light skim. A larger unit means a new reveal, which is formed and finished ready to paint.
Where the plaster is actually disturbed
The ceiling you see is a flat sheet. The skylight is a different thing: a shaft through the roof, lined on the inside, with a neat edge where the two meet.
That edge is called the reveal. In a loft room it is often a sloping plasterboard lining, as deep as the roof build-up, running from the ceiling line to the frame of the window. In a flat roof extension it is a short vertical lining or splay around the opening, often boxed in to hide the upstand.
Work on the roof sends vibration and sometimes small movement into those linings. A hairline at the joint between reveal and ceiling can open when the old unit is lifted out. Dust may drop from the gap behind the lining. Plaster that was already weak, or a joint that was never well taped, is the likeliest to show it. The ceiling field, meaning the flat area a metre or more away, is rarely affected if it is sound and well fixed.
Before anything starts, the room is covered and the area under the opening is protected. The state of the reveal is noted at the survey, so there is a record of what was there before and what is expected to change.
What each kind of swap does to the room
The amount of finishing depends on whether the opening stays the same size. A table makes the pattern easier to see.
| Job | Plaster touched | Finish inside |
|---|---|---|
| Same size, same reveal | Edge only | Filler, light skim, paint |
| Slightly deeper frame | Top of reveal | New board strip, tape, skim |
| Larger opening | Ceiling edge and reveal | New lining and ceiling cut back |
| Flat rooflight, new upstand | Splay or boxing | Reformed lining, skim, paint |
A like for like swap of a roof window is the gentlest case. The new frame takes the place of the old one, and the lining is left as found. Where the new unit sits slightly differently, a strip of board bridges the gap. If you are choosing between a repeat unit and a better one, replacing an old skylight, like for like or a better unit sets out the trade-offs, and putting a bigger rooflight in the same opening shows what a size change involves.
How the reveal is made good
Making good is a sequence, and each step has a reason. The aim is an edge that looks as if it was built with the room.
First the lining is checked for movement. Loose board is refixed. Gaps behind it are filled with insulation so the warmth stays in and the cavity does not whistle. Next, tape is laid over the joints, which stops the cracks that would otherwise return once the paint is on. A thin skim of plaster or a fine filler coat follows, and it is sanded when dry.
The corner between reveal and ceiling is the tricky part. It gets a proper bead where the geometry needs one, or a neat caulked line where a small amount of movement is expected, because a rigid joint there cracks when the roof flexes in wind. A flexible line is the better detail, and painted over it looks the same.
The inside finish is ready for paint once the plaster has dried, which takes a few days depending on the season. We leave the lining primed or filled, and the painting is done by you or by a decorator. Where a room has been decorated lately, the survey says plainly what the paint will need. The quote spells out whether the finish is to decoration-ready, so you know where our work stops.
Keeping the mess and the risk down
A tidy job is mostly preparation, and most of the preparation happens before a tile moves.
Dust sheets cover the floor and any furniture that cannot be moved out. The opening is sealed off from the rest of the house where possible, so a door to the landing stays shut and the dust stays where it starts. A temporary cover goes over the opening whenever the roof is open and work pauses, so the room is protected from weather overnight. Our answer on installing a skylight in the rain covers how that is planned.
There is one more item worth knowing about, and it is the ceiling construction. The 1950s to 1970s homes across the Crawley neighbourhoods tend to have plasterboard ceilings under a pitched roof, which copes well with a lining being cut back. Older lath and plaster ceilings are less forgiving and can lose keys when vibrated, so they are handled with more care and sometimes a little extra support. The survey looks at which you have, and that goes into the written notes for the job. Our page on skylights for post-war homes around Crawley explains why these houses suit the work.
A tidy finish is part of what the 10-year workmanship guarantee stands behind, so the lining is treated as part of the installation and not an afterthought.
Questions about the ceiling after a swap
Will the ceiling need to be redecorated?
The reveal will, and the ceiling next to it may. Fresh plaster shows against old paint, so the reveal is best repainted and a generous margin of ceiling around it. A light coat across the whole room gives the best result.
Can cracks appear a few weeks later?
A fine crack at the corner can show as a house settles to the new unit, and taping and a flexible line at that joint make it far less likely. It is one reason the reveal is taped rather than just filled.
Does a bigger opening mean more plastering?
Yes, because more ceiling is cut back and a larger reveal is formed. The size question is explained in how to size a rooflight for the room.
Is the finishing included in the price?
That is set out in the written quote, line by line, so you can see where making good begins and ends. The general list of items is on what a rooflight quote should include.
To have your own reveal looked at, get a quote. The main service is explained on our skylight and rooflight installation page.