Can You Replace a Slate Roof With Tiles?

Load comes first. Rafters, purlins and walls are sized for the roof they carry, and a heavier covering stresses them in ways nobody planned. Planning Portal guidance brings in building control once a new covering adds 15 per cent or more to the weight carried, and it recommends consulting a structural engineer or surveyor before starting. Approved Document A calls it a significant change in loading when the load on the roof rises by more than 15%.

You can get a rough answer yourself. Every concrete and clay tile has a data sheet giving its weight per square metre, and your roofer can compare it with the slate coming off. If the figures are close, the survey may settle it on its own. If the tile is clearly heavier, expect a structural engineer to look at the timbers, and expect strengthening to be added to the price if the frame falls short.

Old slate roofs also tend to hide their own problems, such as sagging rafters or rotten battens. Those are far easier to deal with now, with the roof stripped, than after the new tiles are on.

Slate can go on a shallower roof than many tiles can. According to BS 5534, natural slate can be laid down to 20 degrees, and Marley's published figures show how widely tile minimums vary: its Edgemere concrete tile needs 17.5 degrees, its Plain tile 35 degrees, and its Canterbury clay tile 40 degrees. A low-pitched slate roof may therefore rule out some of the tiles you were hoping to use, while a few of the lower-pitch profiles stay open.

Measure the pitch before you choose, or ask your roofer to. It is a matter of degrees on the actual slope, not of how steep the roof looks from the road. The data sheet for each tile states its minimum, and the tile must not be used below it, because wind-driven rain can be forced up under the laps.

Fixings matter as well. Tiles are fixed through or clipped to new battens, and the ridge, hips and verges will need new details to suit the new covering. Our roof replacement page explains how a full strip and re-cover is run.

A new covering changes the view from the road, and that is where planning enters. A slate roof in a conservation area, or on a listed house, often carries the character that the area or listing is there to protect. Under the Planning (Listed Buildings and Conservation Areas) Act 1990, any alteration that would change a listed building's special character needs authorisation first, so listed building consent is the route for a new covering there.

Conservation areas are treated as article 2(3) land, which narrows several permitted development rights, and a local Article 4 direction can narrow more. We cannot tell you from here what a particular direction covers, so check with the council's planning team before ordering tiles. For houses in Crawley that is Crawley Borough Council; elsewhere it is the planning authority for your town.

Outside those areas, it is still worth asking whether the change counts as a material change to the external appearance. Our answers on re-roofing in a conservation area and re-roofing a listed building go into the detail.

Slate is a long-lived covering. Corc's roofing guide says that, if well maintained, slate can last 100+ years, while Marley puts concrete tiles at around 60 years, with a caution that it is not a promise. A slate roof that has lost a few slates and has sound battens may be cheaper to repair than to replace, and the repair keeps the lifespan you already have.

Tiles make sense when the slates are failing across the whole slope, when the nails are rusting through, or when a tile is the only choice the planning rules allow on a later extension. Reclaimed slate is also worth pricing before you give up on the original look, as it can cost less than new slate and it matches the old roof.

The best route is to ask for both options in writing after a survey. We check the battens, nails and slate condition, send you photos, and give one total price for each covering, structural work included. Check whether any price includes VAT and scaffolding, and whether the building control body has been told. Our answer on the building control certificate for a new roof shows what to keep afterwards.