A roof lantern is finished inside in one of four ways: a plastered or boarded return up the inside of the kerb, a splayed return that widens towards the ceiling, a shadow-gap edge where the plaster stops short of the lantern frame, or a timber or MDF trim that frames the opening like an architrave. Which one suits depends on the depth of the roof build, the kind of ceiling the opening meets and how much of the lantern's own frame you want to see from below.
Most of the talk around lanterns is about the glass and the shape of the roof. From the kitchen table you look at something else: the edge of a hole in a flat ceiling, and the short walls that lead up to the lantern. This guide covers that part, from the kerb's inner face to the paint line.
What you see when you look up into a lantern
There are three things in view. The first is the lantern's own internal frame: the aluminium or timber bars, the glazing gaskets and the ridge. The second is the ceiling opening, a rectangle cut through the flat ceiling, usually with a thin plastered edge. The third is the part in between, the inner face of the upstand or kerb that the lantern stands on, which runs from the ceiling opening up to the underside of the lantern base.
That middle band is where most lanterns go wrong. On the roof the kerb is a weatherproof, insulated box. Seen from below, if nobody has planned it, it is a strip of raw timber, foil-faced insulation or a rough board return. A lantern can be perfectly weathered and still look unfinished, because the finish was left to whoever was on site on the last afternoon.
Planning it means deciding, before the roof is opened, how tall that band will be, what it is made of and how it meets the ceiling. Those answers also tell you what the rest of the job needs, from the joists to the insulation.
How the roof build decides the return
The height of the inner kerb face comes from the roof build under it, and the build is set by the structure. A flat roof deck sits on joists, the joists carry insulation, and the lantern stands on a kerb above the deck. Add those layers and you have the distance between ceiling and lantern base. In an extension with deep joists and a warm roof, that distance can be generous. In a shallow build, it can be little more than a hand's width.
A tall return gives you something to design with. You can splay it, plaster it to a fine edge or carry a feature finish up it. A short return leaves less room for choice: the lantern base is close to the ceiling, the inner kerb face is a narrow band, and the most attractive option is usually a plain, crisp plaster return.
There is a thermal side to this too. Insulation has to run continuously from the roof insulation up the kerb and around the frame, or the inner kerb face becomes the coldest part of the room's envelope. That shows as condensation first, and as a darkened line of mould later. A good return is built over insulation first and finished second. If you are choosing a kerb height, our guide to roof lantern upstands and kerbs covers the structural side, and the finish follows from it.
The four finishes for the return
Here are the options as they are normally built, with the point of each.
- Plain plastered return
- Plasterboard on a light timber frame, taped and skimmed or taped and jointed, running straight up from the ceiling to the lantern base. It is the neutral choice, and it suits most modern rooms. It is also the easiest to keep clean.
- Splayed return
- The same construction, but the faces lean outwards towards the ceiling so the opening below is larger than the opening at the lantern. The angled faces catch the daylight coming down through the glass and carry it on into the room, which softens the contrast between the bright lantern and the ceiling around it.
- Shadow gap
- The plaster stops a few millimetres short of the lantern frame, leaving a fine, deliberate recess. It reads as a hairline of shade and hides small differences in how the two surfaces meet. It needs the frame to be dead straight, because a shadow gap shows every wobble.
- Timber or MDF trim
- A painted surround that frames the ceiling opening or the base of the lantern. It suits period-style extensions and can hide an uneven edge, though it adds a joint to keep painted and sealed.
None of these is the single right answer. A white plain return under a minimal aluminium lantern looks calm and exact. A splay with a crisp bead can make a lantern in a dark, deep extension look a lot lighter. A trim can tie a lantern to the rest of the joinery. Choose by looking at the room.
Plain or splayed: a short comparison
The choice between a straight and a splayed return is the one most people ask about, so here it is side by side.
| Point | Plain return | Splayed return |
|---|---|---|
| Ceiling opening | Same size as the lantern base | Larger than the lantern base |
| Look from below | Square, architectural, very clean | Softer, with the opening widening into the ceiling |
| Daylight in the room | Strong directly under the lantern | Spread more evenly across the ceiling |
| Best where | The roof build is shallow | The roof build is deep enough to angle |
| Joists and framing | Trimmed to the lantern opening | May need extra framing at the ceiling |
| Edge detail | Right angles, standard beads | Obtuse angles, flexible or adjustable beads |
A splay costs more labour, because every corner is an obtuse angle and the faces have to be true. It also asks more of the structure, since the ceiling opening is larger than the roof opening. We explain the reasoning behind it in more detail on what a splayed rooflight lining is, and the whole process is covered in how a rooflight is finished inside.
Where old ceiling meets new extension
Many lanterns go on extensions, and many extensions are built onto older houses. That makes the join between old and new ceiling a fine detail worth thinking about. A Georgian terrace in St Leonards or a Victorian villa in Torquay may have lath and plaster ceilings in the original rooms, while the extension has plasterboard. A cob cottage in the Culm valley may have lime plaster on its main walls and a modern flat ceiling in the new kitchen.
The lantern ceiling usually sits entirely in the new part, so the opening is plasterboard and no old ceiling is cut. The difficulty comes where the lantern is close to the junction with the old house. Old ceilings move differently from new ones, and a crack can run from the corner of the lantern opening towards the join. A movement joint, or a deliberate break between the old and new ceiling, gives that movement somewhere to go instead of leaving it to find the weakest line.
Where the lantern opening does touch an original ceiling, the cut is made the way it would be for any rooflight in lath and plaster: supported from below, scored cleanly, the laths fixed back, and the edge built up in lime. Our guide to the interior of a rooflight goes through that method.
Corners, movement and why plaster cracks
A lantern is a heavy unit on a kerb, and the structure under it is never completely still. Timber joists move as they take up moisture and settle under load. A new flat roof deflects slightly under its own weight and under wind and snow. The ceiling opening below has four internal corners, and corners are where that movement shows first.
The usual signs of a poor finish are a diagonal hairline crack running out from a corner and a split along the line where the return meets the ceiling. Both are avoidable with a few details:
- mesh or paper reinforcement across the corner, set into the skim;
- a bead at the ceiling edge, so the arris is protected and the plaster has a defined stop;
- a sealant joint, not filler, where the return meets the lantern frame;
- joists and trimmers sized so the opening deflects as little as possible.
Most of this is invisible on the day the work is done, but it decides whether the edge still looks crisp two winters later. It is also why a lantern job should leave time for the plaster to dry fully before the first coat of paint.
The lantern's own frame and the colour inside
Most roof lanterns are aluminium, and many are finished in a different colour inside and out: a dark outside to suit the extension, a white or pale inside to suit the room. That inner frame is part of the finish. Its colour, the line of the glazing bars and the way the ridge runs across the ceiling all sit in your eyeline.
It pays to think of the inside colour and the plaster colour together. A white return under a white frame reads as one calm surface. A white return under a dark frame gives a sharp outline, which can look striking in a modern kitchen and heavy in a small room. The choice between aluminium and uPVC also changes what you see inside, as the sections and gaskets differ; our comparison of aluminium and uPVC roof lanterns covers that.
Where the frame meets the plaster, a thin flexible sealant joint takes up the movement between a metal frame and a plastered return. That joint should run straight and fine, and it is easier to keep that way if the frame was fixed square in the first place.
Plaster, paint and lighting
New gypsum plaster is absorbent and needs a thinned mist coat before the top coats, otherwise the paint soaks in unevenly and the finish looks patchy under the strong light a lantern brings. A matt emulsion hides small unevenness better than a satin does. Ceilings under lanterns get unusual light: bright from above, raking along the return, and sometimes direct on to the plaster. That shows every ripple.
That is a reason to set the return flatter than you think it needs to be, and to light the paint coats from the same direction as the lantern when checking the finish. A lantern shows imperfections in plaster that an ordinary ceiling would hide.
Lighting is worth deciding before the plasterboard goes up. Some owners want spotlights in the ceiling around the lantern, a strip light hidden in a shadow gap or a pendant hanging from the ridge. All of those need cables and fixings in the structure behind the board, and they are far easier to run before the ceiling is closed than after.
Where the house is old and the ceiling is lime, the paint should be a breathable one, such as limewash or a mineral paint, and the plaster around the opening should match. Gypsum next to lime is the usual cause of cracks at a join, and a sealed vinyl paint on lime stops it drying.
Dust, protection and the day the lantern goes in
A lantern is lifted into place, usually by two or more people, and often by a small crane or hoist when the unit is large. The ceiling opening is cut before that, which exposes the room to the roof. After the lantern is in, the weathering is finished on the roof side, and the room is closed in from below.
The plastering happens after the lantern is fixed and weathered. It is a wet trade, so it takes days, not hours: skim coats have to firm before they are trowelled, and the plaster has to dry before the mist coat. Dust sheets and screens go up before any cutting and stay until the plaster is done, floors are covered, and the room is cleaned at the end. If you are planning a kitchen, it is worth deciding whether units, worktops and flooring go in before or after the lantern, because plaster dust is the last thing a new worktop needs.
Your lantern's size also affects the work. A large lantern spans a bigger opening, and a bigger opening means longer return faces to keep flat and a larger ceiling area to finish. Our roof lantern sizing guide explains how to choose the opening from the room, and the finish is easier to get right when the proportions have been chosen well.
Writing the finish down before work starts
Every one of these decisions is easy to agree in conversation and easy to lose by the day the plasterer arrives. So every Brightview quote comes with a finish schedule: a one-page note for the room, written before the roof is opened. For a lantern it records:
- the room, the ceiling and the roof build the lantern stands on;
- the height of the inner kerb face and whether the return will be plain or splayed;
- the material: boarded and taped, skimmed, or lime where the house needs it;
- the edge details: the bead at the ceiling, the joint at the frame, any trim or shadow gap;
- whether the lining is handed over prepared for your own paint or painted by us, and in what kind of paint;
- how dust is managed and the room protected.
That list gives you something concrete to hold against the finished room. If you would like to see how a return would work in your own extension, the full installation process is on our roof lantern installation page, and you can ask for a quote with a finish schedule for your room.