Can you change your roof covering when you re-roof?

Every covering has a lowest safe slope angle. Go under it and weather finds its way beneath the overlaps. The makers publish that figure, and the data sheet for the specific product settles it. On Marley's published list, a concrete plain tile wants 35 degrees, a Lincoln clay pantile 15, and the interlocking concrete profiles anything from 12.5 to 25. Natural slate sits at 20 degrees for the 500 mm size in moderate exposure, per Cupa Pizarras citing BS 5534.

A shallow bungalow roof can therefore rule out the plain tile you had in mind, while a steep gable takes almost anything. For that reason the angle is measured at the survey, before materials come up in conversation at all. Plenty of owners find the decision is half made for them once the measuring is done, and they are glad to know it before they fall for a tile that cannot go on the roof.

A new covering is compared with the one coming off, not with a rule of thumb, and a manufacturer's weight per square metre makes the comparison easy to do. The Planning Portal puts the point where approval is needed at an increase of 15 per cent or more in the weight of the covering. Approved Document A defines a significant change as more than 15 per cent, so the two wordings differ by a hair. We treat roughly 15 per cent as the cue to involve building control and to get the structure looked at before ordering anything.

Heavier coverings put more load onto rafters, purlins and walls that were sized for the old one. That is exactly where the timber check on the strip-out earns its keep, and where a structural opinion is cheap insurance against sagging later.

A lighter covering is not automatically better. Whichever way it goes, the fixings have to suit the tile, and the maker's data sheet sets them for each profile.

A like-for-like replacement is normally outside planning control, because the house looks the same once it is finished. Altering the material can be a different matter. Moving from clay to concrete, or from slate to another tile, changes how the house reads from the road, and on a listed building that sort of change can call for listed building consent.

The Aldwick Road conservation area in Bognor shows why councils care. Arun's appraisal there notes concrete interlocking tiles standing in where slate once was, and encourages owners to bring the original material back. Whether your own street carries a similar expectation, and what the council would want to see on a visible slope, is a question for Arun's planning team, or for the council covering your district.

Our guide to the best roofing material in the UK compares the options on lifespan and cost, and our answer on re-roofing a period property covers older houses.

Building control looks at more than weight. The Planning Portal lists a covering whose fire performance would be significantly unlike the old one's among the reasons to make an application. Two ordinary tile or slate products rarely differ that far, but a move to an unusual material could.

The covering also drags the rest of the roof along with it. A different tile wants a different batten gauge, a suitable underlay and matching ridge and verge fittings. Some ridges are dry-fixed to BS 8612; others are bedded and mechanically fixed to BS 5534. Where the work crosses the thresholds for a thermal upgrade, the insulation has to be looked at too, and our page on roof replacement and new roofs shows how the whole job fits together.

All of this is raised at the survey, which is why the price takes in every layer of the roof, from the timbers up, and not only the tiles on show.

Once the material changes, the old covering is not going back up, so what happens to it needs a decision. Sound clay tiles and natural slates are sometimes worth saving for another use, such as mending a neighbouring slope, an outbuilding or an extension that needs to match. Our answer on reusing old roof tiles explains when salvage makes sense and when it does not.

Most owners reach the final choice in a short conversation after the survey. We tell you which coverings your pitch permits, roughly how each compares in weight, and whether your address brings in any consent. You pick, and what follows is one sum in writing for the whole job, with the old material carted off and the site left tidy. Nobody expects you to decide on the spot, and a second visit to look at samples on the roof is easy to arrange.