The short answer
A tiled conservatory roof is considerably heavier than glass or polycarbonate, and the exact weight depends on the system. A lightweight tiled system is built to keep the load as low as possible, using light tile products, slim insulation and a plasterboard ceiling, while a traditional roof with concrete tiles and timber is much heavier. Ask for the maker's weight per square metre in writing. Building control checks that the frame and foundations can take it.
What adds up to the weight
A roof is more than its tiles. The loads on a conservatory come from several layers, and each one counts. The roof covering is the first: tiles, whether slate-effect composite, steel-cored lightweight or concrete, make up the largest share. Underneath are the battens and counter-battens that hold them, the membrane, the rafters or structural purlins that span the room, the insulation boards and the ceiling finish, usually plasterboard. Add the lantern or rooflights if there are any, and the guttering, flashing and fixings.
Then there are loads that are not part of the roof's own weight. Snow sits on the roof in winter, and wind creates both pressure and lift. People working on the roof, and later maintenance, add temporary loads. The structure must carry all of these with a margin, which is why an engineer looks at the whole picture, and not just the weight of the tiles.
Lightweight against traditional
A traditional tiled roof with concrete tiles, timber rafters and a plastered ceiling is heavy, and it needs a frame designed for that, such as a house-grade wall or steel beam. Most conservatories were built for a light roof, with slim aluminium or uPVC frames and shallow foundations. For them, makers offer lightweight tiled systems, which use lighter tile products and an engineered structure that spans from the house wall to the frame, with the frame doing less work. The weight is cut by design, not by cutting corners. Our page on lightweight tiled roof systems explains how they are built, and the guide to tiled conservatory roofs covers the choices.
Even a lightweight system is heavier than the glazing it replaces. That is the basis of the rule that a solid roof needs a Building Regulations application, in which the building control body checks the frame and foundations.
Comparing with the roof it replaces
The old roof sets the starting point. Polycarbonate sheets are very light, a fraction of the weight of glass, and a glass roof with its heavy glazing bars is heavier again. Replacing either with tiles raises the load by a large factor, which is why people are surprised that the frame needs attention. Lantern roofs concentrate weight at the centre and the supports below them. A hipped or gabled shape, as opposed to a lean-to, spreads load differently across the frame, and the corners and valleys carry more than the open slopes do.
Why the number matters for your frame
The roof's weight passes down through the frame to the base. If the frame is slim or the walls are weak, the load can bow the sides, open the joints and crack the base. If the foundations are shallow, they may settle. A leaning frame also lets water in at every joint. That is why we ask what the base and walls are made of before we recommend a system. Our page on whether your conservatory can take a solid roof sets out the checks on frame and foundation.
Sometimes the answer is to strengthen the frame, for example by adding steel posts or beams, or to use a lighter system. Occasionally the answer is to stay with glass, and to choose an insulated glazed roof instead. We will tell you honestly if the frame is not up to it.
Safety during the work
Weight matters on the day too. Materials are lifted onto the frame in small loads, not stacked on one rafter, and tiles are stored on the ground and passed up. A frame stripped of its old roof is lightly loaded and can be unstable until the new structure ties it together, so the order of work is planned to keep it braced throughout.
Getting the right figure
Ask your installer for the system's data sheet, which gives the roof weight in kilograms per square metre, and ask for the allowance it has made for snow and wind in your area. Ask who has checked the structure, and whether the figure includes the ceiling and the lantern. A structural engineer's calculation for the frame is a sound addition, and building control may ask for it.
Be wary of anyone who says the weight is no problem without looking at the frame. We survey the conservatory, photograph the frame and base and measure the roof, then give a fixed price in writing that names the system and its weight. The larger picture is on conservatory roof replacement in Basingstoke.
Every roof is different. A free survey with photos settles it for yours.
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