The weight test
Rafters, purlins and walls were built to carry a particular covering. A change that adds weight asks more of timbers that have been in place for a long time, and nobody can see from the garden how much spare capacity they have. The rule that governs it sits in two places and the wording differs slightly.
The Planning Portal puts the line at a new covering that is heavier than the old one by 15 per cent or more: past that point, Building Regulations approval is needed. Approved Document A calls a rise of more than 15% in roof loading a significant change. The Planning Portal adds that a surveyor or structural engineer should be consulted ahead of the work.
Weight depends on the product, not on the word clay or concrete. Each tile has a weight per square metre on its data sheet, and the sums must take in the battens and any change of underlay. A thicker tile, or one laid with a deeper lap, adds to the total.
A structure is also not checked by looking at tiles. Rafter size, spacing, condition and any earlier alterations all count, which is why the person checking works from the loft and the plans, not from the ground.
Pitch limits differ by tile
Every tile product has a minimum pitch, the lowest roof slope at which it sheds water reliably. Swapping one type for another can drop the product below its limit on a shallow roof. Marley's pitch table shows how far the limits spread, and the minimum for any product should be read from its own data sheet before an order is placed.
| Product | Material | Minimum |
|---|---|---|
| Plain | Concrete | 35° |
| Double Roman | Concrete | 22.5° |
| Ashdowne | Clay | 35° |
| Lincoln pantile | Clay | 15° |
That spread is why the question is never simply concrete or clay. A clay pantile such as the Lincoln can sit on a much shallower roof than the Ashdowne clay tile, and a concrete tile can have a lower limit than a clay one, or a higher one. Read the figure for the exact tile you plan to buy, because several products from one maker carry different limits, and the nearest-looking sample may not share its neighbour's number.
The page on minimum pitch for roof tiles covers the figures in more detail, and clay against concrete roof tiles compares how the two materials behave.
Appearance, consent and the street
Changing the covering changes how the house looks, and the planning position turns on where it stands. For an ordinary house, Class C of the General Permitted Development Order deals with alterations to the roof, and that normally includes re-roofing. It is not a licence to change the look anywhere.
- A listed house keeps Class C but also needs listed building consent, whenever the change alters what makes the building special, under section 7 of the Planning (Listed Buildings and Conservation Areas) Act 1990.
- A conservation area can bring limits of its own, and the council's list shows where an Article 4 direction removes rights. Swale's Article 4 direction for Faversham names roof coverings and takes in main elevations fronting a public highway.
- Each council lists its own directions, so the answer for your street is on the council's pages, not in a national rule.
Whether a direction applies to your street is a question for the council, and its own list gives the answer. For Dover addresses, the district council's building control team can confirm the route for a re-roof. Elsewhere in East Kent, ask your council whether an Article 4 direction applies. The page on changing roof tiles and planning permission goes through the route.
A sensible order of checks
Before a sample tile from a merchant settles the matter, work the decision in this order. Each step can stop the idea cheaply, which beats finding out after an order is placed.
- Establish what covers the roof now, and its pitch. A roofer reads the pitch from a gable end or with a level against a rafter.
- Collect the weight of each tile per square metre, for the current covering and the proposed one, from the makers' data sheets, and compare them across the whole roof.
- If the new covering is 15 per cent or more heavier, or the sums come out close, arrange a structural check by an engineer or surveyor.
- Test the proposed tile's minimum pitch against the roof you have.
- Ask the council whether the house is listed, sits in a conservation area, or falls under an Article 4 direction.
- Only then ask for a price: one written total, given once the roof has been surveyed.
If the structure cannot take the change, a lighter tile in the look you want may exist. The overview is on the pitched roofing page.
