The short answer
Two things settle it: the share of the building the job affects, and the covering that goes on. The Planning Portal's test lets a small re-cover proceed without an application, but a replacement weighing 15 per cent or more beyond the old covering, or one that would behave differently if fire reached it, brings approval into play. If unsure, ask your building control body before work begins.
The Planning Portal's two conditions
The Planning Portal gives two conditions, and a re-roof normally avoids an application only when both are met. Less than 25 per cent of the building envelope must be affected, and less than 50 per cent of the roof must be affected. The envelope is the whole outer skin of the house: walls, floor and roof, together with windows, doors, roof windows and rooflights.
Picture a semi-detached house where one rear slope is stripped and re-covered. You would work out that slope's share of the roof and its share of the envelope, and check both against the two limits. Strip every slope instead, and the roof condition fails by itself, whatever the envelope figure turns out to be.
Neither share can be judged from the pavement, so the survey comes first. We photograph each slope, set its area against the whole roof and tell you which side of the line the job falls. No council in our area publishes a percentage, so the Planning Portal test is the one we apply.
A heavier covering changes everything
Two triggers sit apart from the percentages. The Planning Portal flags approval once a replacement covering weighs at least 15 per cent above the old one, or would perform significantly differently if fire reached it. Approved Document A, the structural volume, treats a loading rise beyond 15% as significant, so the two documents draw the line a touch differently.
Either way, a change of material deserves a check. Concrete tile, clay tile and natural slate each come in many weights, and the only reliable figures are on each product's data sheet. Compare the old covering with the new one, then add the battens (the timber laths the tiles hang from), because a different tile can need a different batten size.
The Planning Portal also suggests taking structural advice from an engineer or surveyor before works begin. We raise the weight question at the survey and write the covering into the quote by name, so the comparison is on paper.
This rule belongs to Building Regulations, and planning permission is a separate matter. Our answer on planning permission to replace a roof covers that side.
What a council might add
National guidance is the starting point, and councils sometimes describe it in their own words. Basingstoke and Deane's page on building regulations approval names the fitting of new roof coverings, in pitched or flat form, among the alterations that "might also need" Building Regulations approval. That wording belongs to Basingstoke and Deane and applies to its own addresses. It does not say approval is always needed, and it gives no percentage.
For a house in Test Valley, which includes Andover, the rule to follow is the Planning Portal's two conditions and the weight check above. Where a council page seems to differ from the national guidance, ask your building control body which applies to your address.
It also helps to know who decides. Local authority building control deals with your application, or a registered building control approver does. That is a private firm listed under the registration regime that began on 6 April 2024, although private building control itself is older.
The National Park authorities handle planning only. Inside the South Downs or the New Forest National Park, building control still sits with the district or unitary council.
Finding your building control body
For a Test Valley address, the safe wording is your building control body. Check with Test Valley Borough Council who handles building control for your street.
Elsewhere in our area the picture is clearer. Wiltshire Council runs its own service, reached on 0300 456 0113. West Berkshire is served by Building Control Solutions, which the council runs with Wokingham Borough Council, on 0300 790 0580. Basingstoke and Deane, Winchester, New Forest District and East Hampshire councils all keep in-house building control teams.
If the answer is that approval is needed, the paperwork matters later. When the building control body is satisfied it issues a completion certificate, and our answer on the completion certificate for a new roof shows how that works and why buyers ask for it.
If you are unsure which side of the line your job falls, send us the covering you have and the one you want, plus a few pictures of the slopes. We will tell you at the survey whether weight or fire performance is likely to matter, then price the work on the roof replacement page's terms: one written total.
