Can You Insulate a Conservatory Roof?

The lowest-cost route is a lining fitted inside the existing roof. Thermal blinds are the least effort of all, and they come down in summer. Insulated boards do more but cut daylight, so decide whether you want a bright room or a warm one before you buy. Foil-backed boards, insulated panels and thermal blinds all sit under the glazing and cut heat loss in winter and heat gain in summer.

What do internal kits do well?

They make the room more comfortable for less money than a new roof, and they leave the structure alone. They also give some control over glare. The limits are that the old glazing stays in place above them, the join to the walls is hard to seal, and the roof can no longer be seen from inside, which hides leaks and growth until a stain appears on the lining.

A lining sits against a cold surface, and the air trapped above it can turn damp quickly. Anyone selling a kit should explain what stops that happening. A kit that blocks every gap and leaves no way for moisture to escape is the one most likely to cause the damp it was meant to cure, so ask the question before you buy.

A solid roof with insulation built into it is the thorough answer. The old glazing comes off and a new roof, made up of structure, insulation, a vapour layer and a covering, takes its place.

Does a new insulated roof need approval?

Yes. Under the Planning Portal's guidance a replacement roof on a conservatory falls under Building Regulations. Part L sets the energy standard, and Table 4.2 of Approved Document L (2021 edition) gives 0.15 as the roof U-value for new elements in an existing dwelling. The U-value is a measure of heat loss, and a lower figure means less heat escapes. The 2026 edition takes effect on 24 March 2027.

The frame has to cope with the extra weight too, and a structural check is part of any sensible plan. We look at the frame before we quote, and ask for the U-value of the finished roof in writing, along with the thickness and type of insulation that achieves it. Our page on a conservatory frame for a solid roof covers the weight question, and the wider options sit on the conservatory roofs page.

Insulating a roof moves the cold surface. Before, it was the glazing, and condensation ran down it. After, the cold surface can sit within the build-up, out of sight.

Can insulation make condensation worse?

If it is done badly, yes. Warm damp air from cooking, drying clothes or simply breathing gets into the build-up and condenses on whichever layer sits below its dew point. A sealed vapour control layer under the room lining keeps most of that air out, and a ventilated gap or a tested sealed design deals with the rest. BS 5250 is the reference for how moisture should be managed. Rooflights and lanterns are weak spots for heat loss, so count them when you compare options. A cheap humidity meter on the wall tells you whether the room is running damp, which is useful before and after any work.

Our answer on whether solid conservatory roofs need ventilation sets out the options, and the guide to conservatory roof condensation covers glazed roofs. For the wider set of choices, see our conservatory roofs page.

Foam sprayed under a roof looks tempting, but it brings problems of its own.

Is spray foam a good idea?

The Energy Saving Trust, writing about foam on a leaking roof, says plainly that it does not recommend it. Foam also hides the roof from inspection. RICS's consumer guide asks you to raise it with your mortgage provider before any such product is installed. Removing foam later is a job of its own, which is better avoided in the first place.

Do not stuff loose insulation into gaps behind the glazing, and do not block vents or weep holes on the frame. Both trap moisture where it can do harm. If a company recommends spray foam for a conservatory roof, ask for the maker's evidence in writing and compare it with the guidance above.

Choose between a lining and a new roof by looking at the glazing first. If the sheets are old, cloudy or leaking, spending money on a lining under them makes little sense. We look at the roof, photograph it and quote a single written price for whichever option suits. Tell us about the room and its current roof, and we book the survey.