The short answer
When it goes past the limits in the Planning Portal guidance: 25 per cent of the building envelope or 50 per cent of the roof, structural changes, a covering 15 per cent or more heavier, or a significantly different fire performance. Small repairs sit well below those lines.
Building control is separate from planning. It checks that building work meets the Building Regulations for structure, fire safety and energy use, and a roof falls under it in particular cases.
Q3.1What are the usual limits?
The Planning Portal sets out when a re-roof or repair does not normally need an application: less than 25 per cent of the total building envelope affected, and less than 50 per cent of the roof. Beyond that, approval is needed, and the work can carry a requirement to improve the roof's insulation.
Q3.2Do weight and fire performance matter?
A new covering that increases the roof's weight by 15 per cent or more needs approval, and so does one that performs significantly differently in a fire. Approved Document A treats a load increase of more than 15 per cent as significant, so the structure gets checked whenever the material changes.
Q3.3Who deals with building control here?
The district council runs building control jointly with South Oxfordshire under the Southvale name, while a registered building control approver offers a private route. Which applies to your job, and who submits the notice, is settled with you at the survey.
Q3.4Is planning a separate question?
These are a separate matter from building control. A job can need one, both, or neither, and we tell you which at the survey.
For larger works, the application is made before the job starts, not afterwards, which is why we raise it early. A tiled roof that needs stripping to the rafters is the usual trigger, since replacing the whole covering and the battens on a large pitch can pass the roof limit by itself. Our roof replacement page explains what that kind of job involves.
On a small village house, a simple conversation at the survey is normally enough to settle the route: we measure the roof against the limits, note the weight of the old and new coverings, and write the answer into the quote. Where building control is involved, the notice is lodged ahead of the first tile coming off, which saves you chasing paperwork later.