The short answer
A conservatory overheats because sunlight passes through the glazing, warms the floor and furniture, and the heat cannot escape. The fix is to block some of the sun before it enters and to let hot air out. Blinds, solar control film and roof vents help at modest cost. Replacing a glazed roof with an insulated solid or tiled one addresses the cause directly.
Why glass roofs overheat
Sunshine is short-wave radiation. It passes through clear glazing and heats the floor, furniture and walls inside. Those surfaces then give off heat as long-wave radiation, which glass and polycarbonate are far worse at letting out. The heat is trapped, and the room warms until it matches the loss through the glazing and any open vents. This is the greenhouse effect in a small and familiar form.
The roof is where most of this happens. It is the largest glazed surface, it faces the sky, and on a sunny day it receives sun for much longer and at a steeper angle than the walls do. A south or west-facing conservatory with a fully glazed roof is the classic overheater, but any aspect can struggle in a hot spell if the roof is thin and the ventilation is poor.
Cheaper measures that take the edge off
If a full roof change is not planned, there are several things to try, listed here from the least invasive.
- Blinds. Blinds fitted inside the roof help, but external shading works better, because it stops the sun's heat before it passes through the glass. Roof blinds are widely used for this reason.
- Solar control film. A tinted or reflective film on the glazing reduces the amount of heat that enters. Our page on conservatory roof film looks at what it does and where it falls short.
- Ventilation. Opening roof vents and side windows lets hot air escape, and doing so at both low and high level creates a draw. A roof that has no vents at all traps the hottest air at its highest point.
- Roof windows. Fitted into the roof, they can add a high-level outlet for hot air. See our page on roof windows in a conservatory.
- Everyday habits. Closing blinds before the sun reaches the room, and opening vents early in the day, beats trying to cool a room that has already baked.
Work through these in order and keep a rough log. If the room still climbs past comfort on a hot afternoon with every blind down and every vent open, you have established that the roof itself is the limiting factor. That is useful evidence before you spend on a bigger change, and it tells a roofer exactly where to concentrate.
Be wary of overhead fans and portable coolers used as a cure. They move or cool air for a while, but they do nothing about the sunlight arriving through the roof, so the room keeps taking in heat and the running costs mount up through the summer.
Why the roof type matters most
These measures help, but they treat a symptom. The underlying issue is a roof that lets sun in and has little ability to resist heat. Changing the roof treats the cause.
- Solar control glass. A glass roof with a coating designed to reflect part of the sun's heat reduces the load while still letting daylight through. It is a good fit for owners who want to keep the light.
- Solid insulated roof. Plasterboard and insulation below, tiles or another covering above. It blocks direct sun and slows the passage of heat, so the room tracks the house temperature more closely. You lose the overhead light, though roof windows or a lantern can restore some of it.
- Lightweight tiled roof. The same idea with a lighter build to suit an existing frame.
A solid roof is a different structure, so the Building Regulations process applies to it as alteration work. Weight, frame and base are all checked. Our guide to a solid conservatory roof goes through the trade-offs.
The same fix helps in winter
A roof that overheats the room in July usually leaves it cold in January, because thin glazing is poor in both directions. A change of roof that deals with summer heat normally helps in winter too. If you are weighing the two seasons together, our answer about a cold conservatory covers the winter side in more detail.
Not everyone wants the room to feel like part of the house. Some owners keep a glazed roof for the light and manage the heat with shading and ventilation. That is a sensible choice if the room is mostly used in spring and autumn. The roof should match how you use the space.
Listed houses and conservation areas
Shading and ventilation measures are mostly reversible, but a new roof, fixed external blinds or a change to the roof glazing can affect appearance. A listed house calls for a word with the council before you touch the roof of an attached conservatory, since listed building consent runs apart from planning. The same caution applies in a conservation area. Our page on conservatory roofs on listed buildings explains how consent works.
B&NES keeps conservation and planning contacts on its website, and the other councils around Bath do the same for their areas.
When overheating and damage go together
Sun, heat and ultraviolet light age glazing and seals, and an overheating roof may also be one that has begun to fail. If sheets are yellowing, seals are cracking or leaks have started, the heat problem and the damage are probably linked, and replacement can cure both. If damage has come from a storm, see our answer on whether home insurance covers a conservatory roof before any work begins.
A survey of your conservatory, with photographs of its own roof details, lets us put one written, fixed price on the route you pick. The whole range is described on the conservatory roof replacement page.
