The answer
A like-for-like swap on the same opening should leave the ceiling largely as it was, because the work happens on the roof and the frame, not on the plasterboard. The room is covered before we start, and any small disturbance at the edge of the reveal is made good. The condition that changes this is size: a bigger opening, a rebuilt kerb or a damp, stained reveal means plaster and decoration need work, and the survey will say so.
Where the work happens
Most of a rooflight replacement is done from the roof. The old glazing comes off from above, the new unit goes on from above, and the weathering is finished outside. The ceiling below is not cut or lifted when the opening stays the same size.
What sits between the glass and the room is the reveal: the lined shaft, or splay, between the underside of the rooflight and the plane of the ceiling. It is plastered, boarded or lined in plasterboard, and painted. When the new rooflight is the same size and sits on the same kerb, the reveal stays as it is, and the new frame meets it at the same line as the old.
That is the best case, and a common one when we are replacing misted rooflights. It also depends on how the old frame was fixed and sealed, because internal trims and sealant lines are part of the reveal finish.
Where the junction between frame and reveal is disturbed, it is a small matter of filling and repainting a line a few centimetres wide. We cannot promise that no mark will ever be left at that edge, since an old frame that has been in place for years sometimes takes a little of the finish with it when it comes away.
How the room is protected
Before the old unit is touched, the floor and furniture under the opening are covered with sheeting, and anything fragile or loose is moved out of the way. A dust sheet laid under the opening catches what falls: old sealant, flakes of paint, dirt from the top of the kerb and the occasional drop of water trapped in the old unit.
We also think about what will come down when the old glazing is lifted. A misted unit can hold standing moisture in the gap, and an old frame can shed gritty residue. Lifting carefully, and working from above with the opening covered below, keeps that from reaching the room.
For a large or heavy rooflight, such as a big lantern, access matters too. Passing glass down is not needed, because the unit is craned or hand-lifted on the roof, but the route through the house is still worth a thought. If your hallway is narrow or the stairs turn, tell us at the survey. We will cover floors along any route we need to use.
Finally, the weather is watched. The opening is never left uncovered while the forecast is uncertain, and the new unit is closed in before we leave the roof.
What is made good, and what is not
After the new rooflight is in, we deal with the junction on the inside. That means checking the sealant or trim where the frame meets the reveal, filling any small gap or chip, and leaving the edge ready to paint. For an ordinary swap, that is the extent of it.
Painting the reveal to match the rest of the ceiling is a matter of agreement. If you would like us to leave the edge primed and ready for your own decorator, we do that. Colour matching an older ceiling can be harder than it sounds, since white paint yellows with age and new paint on one patch will show, so many people choose to repaint the whole ceiling or the whole reveal.
A different case is a reveal that was already damaged. If the old unit was misted for a long time, you may find a tide mark, flaking paint or damp-stained plaster at the base, from years of surface condensation. That is not caused by the replacement, but it becomes visible once the new unit shows up how tired the surround is. We point it out at the survey where we can see it, so it is in the plan from the start.
Where there is any sign of damp in the plasterboard, it is dealt with before the new unit goes in, not covered over.
When the ceiling does need work
Some jobs do involve the plaster, and it is better to know in advance.
If the new opening is larger than the old, the ceiling is cut back to the new size, and the new reveal is boarded, filled and finished. If the kerb has to be rebuilt, the lining inside may be disturbed, as the new upstand and its insulation change the profile of the shaft. If the rooflight changes type, for example a flat unit being replaced by a lantern, the inside shape of the opening can change with it. In each of these, plastering and decorating are part of the job, and the written quote says so and lists what is included.
Moving the position of the rooflight, even by a modest distance, means a new hole in the ceiling and a patch to close the old one. Patching a ceiling so the join does not show is skilled work, and a skim over the whole ceiling often gives a better result than a small patch.
All of this is covered in replacing a rooflight on an existing kerb, which explains what happens on the roof side.
Getting a tidy finish on a grey-day room
The room under a rooflight is usually chosen to be bright, and a bright room shows every flaw. A raking light from a new rooflight picks up the line of a patched ceiling or a patchy repaint more clearly than a dim light would.
It helps to decide up front what finish you want. A white or pale reveal bounces more light into the room on a dull day, and a splayed reveal spreads it wider than a straight one. If the old reveal is a dark or yellowed colour, repainting it white is a cheap way to make the new rooflight work harder in winter.
Whatever you choose, mention it at the survey. The written quote is fixed after we have seen the roof, and anything you want done around the reveal can be priced into it, so there is no surprise on the day. The work is installed to current Building Regulations, with the Building Control notification handled by us where it applies, and a 10-year guarantee on our workmanship. If the cause of the mist is still on your mind, why rooflights mist up covers it.