The short answer
Repairs and re-covering do not normally need approval where the work affects less than 25 per cent of the building envelope and less than 50 per cent of the roof. A full relay of a lead roof often goes beyond that, and then approval applies and the roof's insulation may need bringing up to standard. A covering that is 15 per cent or more heavier also needs approval.
The two tests that decide it
The Planning Portal sets out when re-covering a roof is covered by Building Regulations. For repairs and re-covering, approval is not normally required while the work touches less than 25 per cent of the whole building envelope and under 50 per cent of the roof itself. Both conditions have to be met together. The building envelope means all the outer surfaces of the building, the walls and roof together, so a small roof relative to the house can fall below the limit while a large one cannot.
For leadwork, that means a patch to a flashing, a new valley lining, a replacement section of gutter bed or a local re-leading will almost always be well below the thresholds. Relaying a flat lead roof across a big extension or a whole terrace house is another matter, because it may well affect more than half of the roof it forms part of.
The advice on thresholds does not replace a conversation with building control. It is a rule of thumb from the national guidance, and your own roof, its size and the extent of the work decide the answer. We measure the work at the survey and flag the point where approval comes into play.
What changes when approval applies
When a relay passes the thresholds, the roof counts as a thermal element, and the insulation in it may have to meet today's standards. The Planning Portal says you may be required to upgrade it. Approved Document L of the Building Regulations, in its 2021 edition, asks that a replacement roof element does no worse than the old one and meets the table of limiting values for new fabric in existing homes, where the roof element is given as 0.15 W/m²K.
On a flat lead roof, that usually means looking at what lies beneath the lead. Old decks often have little or no insulation, or insulation that sits between the joists in a cold roof with a ventilated void. Upgrading may mean adding insulation above the deck in a warm roof arrangement, and the lead is then laid over the new build-up. That changes the depth of the roof, so it can affect the upstands at walls and thresholds. It also adds cost, which is why it should be discussed before the price is agreed.
Moisture control and ventilation need to be designed with it. Lead roofs have to be built so that condensation does not collect under the deck, and the correct build-up depends on the construction. A survey of the existing roof tells us what is there.
Weight and structure
The second trigger in the national guidance concerns weight. Approval is also required if a new material makes what covers the roof 15 per cent heavier or more, because the structure beneath may need to be checked under Approved Document A.
Lead is heavy. It is also commonly replaced by lead, which does not alter the load. But if the existing covering is something lighter, such as asphalt or felt, or if the new lead is a heavier code than the old, the comparison needs to be made. A code 5 sheet weighs 25.40 kg/m², and a code 8 sheet 40.26 kg/m². That difference matters when it is repeated across a whole roof.
Changing the covering altogether, for example moving from lead to a different system on a flat roof, is a change in weight that has to be calculated. Repairs such as those described under lead valleys or a blocked hopper head are examples of repairs where no weight change occurs, so these sit well within the safe side of the rules.
Who deals with the application, and other permissions
If approval applies, you can apply to the council's own building control, which for Bath means B&NES, whose office is in Manvers Street, or you can use a registered building control approver, a private firm registered under the system that began in April 2024. Whichever you choose, the work is checked as it progresses and signed off at the end.
If your job is notifiable, we tell you what the rule requires and look after the Building Regulations paperwork. You should not expect to learn about a requirement from a surveyor months afterwards, when a sale is under way.
Building Regulations are separate from other consents. A listed house may need listed building consent from B&NES where the work touches its character, which can include re-leading or a change of material, and a conservation area brings considerations of its own. The two sets of rules run side by side. Our guide to listed leadwork covers consent, so raise it with the council ahead of any work.
Practical steps before you book
If you are planning lead work and wondering whether approval applies, a few steps will settle it quickly. First, decide whether the work is a repair of part of the roof or a relay of a whole area. Second, ask for the area to be measured, as a proportion of the roof and of the building. Third, ask what is under the lead, since the answer decides whether an insulation upgrade is likely.
Then check the details of the covering. Rolls and drips are part of how lead is laid, and they are described on our page about lead rolls. Neither changes the Building Regulations position of itself.
Finally, do not rely on a general answer when the roof is unusual. Mansards, bays, roofs in flats and roofs joined to a neighbour's can each raise further points, and the right place to confirm is your building control body. Our lead roofing team surveys your roof, photographs it and gives a fixed price in writing, and if an application is needed we make it. The Planning Portal's own guidance on re-roofing and Building Regulations is worth reading beside this page.
