Which glass is best for a conservatory roof?

Glass is chosen to solve a problem, so start by naming yours. A room that faces south or west gets strong sun for much of the day, and the glass has to deal with glare and heat. A north-facing room is the reverse: it stays dim and loses warmth, so it needs the clearest glass you can get and the best insulating value. A room used as a dining area in the evening has different needs from a playroom used all day.

It also helps to be clear about what the glass cannot do. No pane fixes a frame that leaks, a roof with no ventilation, or a room with single-glazed walls and a bare floor. If summer heat is the real complaint, read our guide to why a conservatory gets too hot before spending on the roof. If winter cold is the complaint, a glazed roof may be the wrong tool altogether, and a solid roof may suit better.

Most glass conservatory roofs use sealed units made of two panes separated by a gap, because a single pane loses heat quickly. The two panes are not always the same. A common specification pairs a toughened outer pane with a laminated inner pane. Toughened glass is heat-treated so that it breaks into small blunt pieces. Laminated glass has a plastic interlayer that holds the pieces together when it cracks, so a damaged pane stays in place instead of dropping into the room.

Over a seating area, a laminated inner pane is the specification we would ask for. Whatever you are quoted, ask what each pane is, what the gap holds, and what the unit weighs, because weight drives the frame. Glass is heavier than polycarbonate. If the new roof will be noticeably heavier than the old one, Planning Portal guidance is to have the frame looked at by an engineer or surveyor before work begins, and a good installer will already have arranged it.

A solar-control coating is a thin metallic layer on one pane, designed to reflect part of the sun's heat while letting daylight through. It suits south and west rooms where overheating is the complaint. A low-emissivity coating works the other way round: it helps keep room heat from escaping through the glass, which matters most when the room faces north or is used in winter.

A tint is a different idea. Tinted glass absorbs part of the sun and glows warm, and it cuts glare, but it also darkens the room and changes the colour you see outside. Some manufacturers combine layers in one unit, and the trade-off is that the more the glass is asked to do, the more it affects how the room looks. Ask to see a sample against your own window frames in daylight before you order, because a showroom pane under strip lights tells you very little about how it will look over your own garden.

Self-cleaning glass carries a coating that breaks down some of the dirt in daylight and lets rain wash it off. It is a convenience, not a maintenance-free promise, and we cover it in detail in our answer on self-cleaning conservatory glass. Whether it is worth having depends on the shade, trees and birds around the room.

Rain noise is the other thing people notice. A glass roof is quieter than a thin polycarbonate sheet, and heavier laminated units are quieter again, but heavy rain will still be heard. Appearance depends on the frame as much as the glass: slim aluminium bars look light, bulkier white frames look heavier. Frames, sealants and glazing gaskets all age at their own pace, so ask how the units are held in and how a damaged one is replaced. Our comparison of glass and polycarbonate roofs shows how the two stack up on noise, heat and cost.

When you get a quote for a glass conservatory roof, a short list of questions sorts the good from the vague. Which glass is being supplied, and does the paperwork name the make of unit? What is in each pane and what coating, if any, is on it? Who checked the frame and the weight, and is that written down? Is the roof installed with proper flashings against the house wall, and who deals with the building control side if one is required?

Also ask what happens to the old roof and who takes it away, and how long the work is expected to take. We survey the existing frame, record the weak points in photographs and say whether new glass, a refurbishment or a different roof type would suit. The written quote gives one total, with the glass specification named in it. If you are weighing glass against a tiled roof, our page on conservatory roof replacement sets out each route.