Conservatory roof replacement in Farnborough

A conservatory with a glass or polycarbonate roof was designed around a light load. The roof sits on the window frames, the frames sit on dwarf walls (the low brick walls that run round the base), and the dwarf walls sit on footings of their own. Every link in that chain was sized for sheets and bars. A tiled roof adds tiles, battens (thin timber laths that carry each course), insulation and a plasterboard ceiling, so the frames and walls are checked before anything else.

The table sets out the published wording. On the Planning Portal's guidance, a new covering that increases the weight of the roof covering by 15 per cent or more needs Building Regulations approval, and it advises having the roof checked by a structural engineer or surveyor beforehand. Approved Document A treats a load increase of more than 15% as a significant change in roof loading. The Planning Portal's answer on conservatories is direct: "A new roof must comply with building regulations to ensure it is structurally safe, energy efficient and properly ventilated."

What a structural check looks at

The check starts at the ground. We look along the dwarf walls for cracks, for brickwork pulling away from the house and for any sign that the base has settled. Then the frames: whether the uPVC or aluminium sections stand square and plumb, whether the doors still close cleanly, and whether the corner posts are already carrying load. We also look at how the conservatory is tied into the house wall, because a heavier roof will bear against it. Inside, a sagging ridge or a bowed eaves beam shows a frame struggling with the roof it has now. Where the answer is unclear, a structural engineer looks at it before we put a figure on anything.

When the frames need help

Some conservatories can take a lightweight tiled system on their existing frames once those are shown to be sound. Others need a ring beam, a structural beam fitted round the top of the frames to carry the new roof and spread its weight, or new posts at the corners. Some need new frames, and a few need new walls and footings, which makes the job closer to a small extension. The order of work follows from that: walls and frames are made good first, then the roof structure goes on, then the covering, so a hidden fault is never roofed over. Our guide on whether a conservatory frame can take a tiled roof walks through each outcome.

Building control is part of the job from the first drawing. For Farnborough, Aldershot, Fleet and the other Hart towns, the council service is the Hart and Rushmoor Building Control Partnership (01252 398715). A registered building control approver is the alternative route.

Pitch is the angle a roof slope makes with the horizontal, and every tile has a lowest angle at which its maker says it will keep wind-driven rain out. A conservatory roof can be shallow. A lean-to runs up to the house wall and has to stop below a first-floor sill or the eaves above it, and a Victorian or Edwardian style roof is limited by its own short span. The angle the original builder chose was set for glass or polycarbonate, not for tiles.

The table gives Marley's published minimums for its lower-pitch tiles and, for contrast, its plain tiles. The Mendip 12.5 interlocking concrete tile is listed for slopes down to 12.5°. The Mendip, the Wessex and the Lincoln clay pantile are listed at 15°, and the Edgemere at 17.5°. The concrete plain tile needs 35° and the Canterbury clay plain tile 40°, which rules plain tiles out on a low conservatory. For natural slate, Cupa Pizarras reports a BS 5534 minimum of 20 degrees.

Lean-to, Edwardian and Victorian shapes

A lean-to has one slope, and its pitch is set by the height available at the wall. An Edwardian style roof has a ridge with hipped ends over a squared front. A Victorian style roof adds a faceted, rounded front, with several small hips meeting at one point; a hip is the capped edge formed where two roof faces join at an outer angle. More hips mean more cut tiles and more capping, and each hip needs its own fixing. We measure every facet, because the front facets can sit at a different angle from the main slopes. A gable-fronted conservatory, with an upright triangle of glazing at the front, has a ridge running back to the house and two plain slopes, which tiles cover more simply.

The figure12.5°Mendip 12.5: down to

Lightweight tiled systems

A lightweight tiled roof uses an aluminium frame with synthetic or composite tiles or slates, designed to reduce the load on the existing frames. Each system has its maker's own data sheet, with minimum pitches and loads for that product, and the data sheet overrides any general table. We check that the existing frames match what the system maker asks for before we name one. Our guide to lightweight tiled conservatory roofs compares them with a full tiled build on new rafters.

Where the measured pitch sits below every option, the honest answer can be a different roof form. A flat roof with a membrane covering, or new glass, may suit a very low lean-to better than any tile, and we would rather say so at the survey than fit a tile outside its range. Raising the pitch is sometimes possible on a detached-style conservatory with room above it, though that changes the look of the house and can bring in planning questions.