The short answer
Re-covering a small flat roof often needs no application, but a new roof or a major renovation can. Under Part L a new waterproof layer can pull the roof's insulation into the job, so an upgrade may be needed. Southvale or a registered approver can confirm.
Garages, kitchen extensions and porches with flat tops are part of village life around Abingdon, and they usually need attention before the pitched roof does. The rules turn on how much of the roof and the building is affected.
Q3.1When is an application needed?
Planning Portal guidance gives two limits, 25 per cent of the total building envelope and 50 per cent of the roof, and staying below both normally means no application. A small garage roof usually falls under them, since it is a modest part of the building. Ask before you start rather than after, because regularising finished work is slower and can mean opening up the roof. A full-width kitchen extension may not.
Q3.2What does Part L add?
Approved Document L lists a replacement waterproof membrane among the works that renovate the roof as an insulating element. Where more than 50 per cent of that surface is renovated, all of it should reach the improved U-value, 0.16 W/(m²·K) for a roof. In practice that can mean new insulation above or below the deck.
Q3.3Who do I ask?
Southvale Building Control is the council route, a joint team for the Vale of White Horse and South Oxfordshire, with a registered building control approver as the private option. Our survey says whether the job looks notifiable, and we make the notification when it is. Keep the completion paperwork with the deeds, because a buyer's solicitor may ask for it years later.
Q3.4Which covering suits a Shippon extension?
EPDM rubber, GRP fibreglass and torch-on felt each suit different roofs and budgets. Our flat roofing page sets out the differences and the lifespans that third-party guides publish. Whatever the covering, the fall of the deck matters, because ponding water cuts short the life of any membrane.