The short answer
Yes, but only with a solid roof. A glass or polycarbonate roof has no space for a ceiling, while a tiled or solid system has rafters, insulation and a plasterboard layer that can be skimmed like any other ceiling. It adds weight, must comply with the Building Regulations, so ask your building control body first, and has to be built so damp cannot collect inside it. Lighting is usually recessed into the new ceiling.
Which roofs can take a ceiling
A ceiling needs something to fix to and something to hide. A glass or polycarbonate roof has neither: the glazing is the roof, and a plaster layer under it would cut off the light and trap damp.
A solid roof has the depth. Timber rafters, usually with insulation between them, carry plasterboard on their underside. The boards are taped and jointed, then skimmed with plaster in the same way as a ceiling in the house, ready for paint.
Some systems come with the structure and plasterboard supplied as part of a kit, and others are built on site. Both end in a plastered finish, but the lining behind it differs, and so does the weight.
The shape matters as well. A simple lean-to takes a flat or sloping ceiling easily. A hipped or Edwardian roof gives a ceiling with angles that follow the rafters, which can be plastered to follow the lines or boxed in. Our guide to a solid conservatory roof with a lantern shows how openings are framed into the ceiling.
Ask what the plasterboard is fixed to, and how the joints with the house wall are finished, because that is where cracks tend to show. A hip-ended roof also has valley and hip lines inside, and a tidy plasterer can set those out so they look deliberate.
Weight, structure and approval
A plastered insulated roof is far heavier than glazing. The frame, the dwarf wall and the foundations must carry it, and an engineer's check is sensible before design is fixed. The Planning Portal's re-roofing test flags a covering 15 per cent or more heavier, and swapping glazing for a solid insulated roof goes well beyond that.
A new solid roof must comply with the Building Regulations, so ask your building control body first; an application brings inspections as the work goes on. The inspector will look at the structure before it is hidden by boards, and at the insulation before it is covered, so the plasterer should only start once both stages are passed.
Part L sets the energy standard. Table 4.2 of Approved Document L sets a limit of 0.15 W/m²K on a replacement roof for an existing home. A lantern in the ceiling is a rooflight, held to 2.2. Roof windows are treated separately, at 1.4 or Window Energy Rating Band B.
Your building control body confirms which figures apply to your conservatory, because the answer turns on how it connects to the house.
Lighting and fittings
A plastered ceiling gives you options that a glazed roof does not. Recessed spotlights can sit in the board, a pendant can hang from a joist and a ceiling fan can be fixed to a strengthened point. Plan the positions before the boards go up, so the electrician can run cables and the carpenter can add support. Mark the fan or pendant point on the rafters while they are still visible, because it is hard to find afterwards.
Recessed lights cut holes through the ceiling, and each hole is a place where warm air can leak into the roof. Choose fittings that suit the insulation arrangement and ask the electrician what clearances the fittings need. A cable run in the roof space has to be laid with the insulation in mind too.
Light levels change when the glass goes. A plastered ceiling is a solid surface, so natural light comes from the walls, a lantern or roof windows. Our answer on a tiled roof making the room darker looks at that trade-off, and good ceiling lighting makes up much of the difference.
Painted white or a pale colour, the new ceiling also bounces light around the room. A matt finish hides small ripples in the plaster better than a gloss one, and it is kinder to light from spotlights.
Keeping the roof dry inside
Insulation and plaster bring a damp risk. Warm room air carries water vapour, and if it reaches the cold side of the insulation it condenses inside the roof where it cannot be seen. Approved Document C, paragraph 6.2, expects roofs to be designed so that this interstitial condensation does not harm their performance.
The defence is in the layers: a vapour control layer under the insulation, a sealed ceiling, and ventilation above the insulation where the design needs it. Gaps around downlights and at the wall junction undo the work, so they are sealed.
Plaster itself needs drying time, and the room should be kept ventilated while it sets. Hairline cracks can open at the junction with the house wall as the structure settles, and a flexible joint there is cheaper than repeated filling.
On the survey we look at the frame, the wall junction and the ventilation, and we photograph each. The conservatory roofs hub lists the solid roof types, and our price arrives in writing once we have seen the room.
