A neighbour re-tiles a roof and nobody from the council appears. Another has a roof replaced and the paperwork arrives afterwards. Both can be correct. The difference is how much of the roof was touched, what went on it and whether anything structural changed. This guide is about those application thresholds only; the insulation upgrade that can follow is a separate subject, covered in our Part L guide.
It describes the position in England using the Planning Portal's published guidance and the Approved Documents. Treat it as orientation rather than legal advice, and put your own roof to your building control body. At the survey we tell you which tests your job is likely to meet, and any notifiable work is notified by us on your behalf. The wider service is on our roof replacement page.
The two area tests, and why both must be passed
The Planning Portal says an application to building control is not normally needed if two conditions are both true. Less than 25 per cent of the total building envelope is affected. And less than 50 per cent of the roof is affected.
The envelope is the outer skin of the building: roof, external walls, floors in contact with the ground, and the openings in them. A re-roof does not usually touch all that, so the roof test normally governs. But the two conditions are joined by "and", so passing one is not enough.
A common misreading
It is sometimes said that work over 25 per cent of the roof needs approval. That is not what the guidance says. The roof limit is 50 per cent; the 25 per cent figure belongs to the envelope. On a small house the two can come close, because the roof is such a large part of the shell.
| Test | Limit for no application |
|---|---|
| Building envelope affected | Less than 25 per cent |
| Roof affected | Less than 50 per cent |
A full strip of every slope is over both limits. Re-covering one slope of a four-sided hipped roof might not be. We work out the share at the survey from measured areas, and the figure goes into the quote.
Triggers that apply whatever the area
Even a small area can need approval if the work falls into one of three further categories. The Planning Portal lists them: structural alterations, a covering whose reaction to fire departs markedly from the old one, and any covering that makes the roof 15 per cent or more heavier.
Structural alterations
Changing a rafter, raising a ridge, cutting a purlin or opening a roof for a new window are structural. A roof window in an existing roof is covered in our skylights section, including its planning rules. Even if the area is small, a structural change brings Building Regulations into play.
Fire performance
A roof covering has a fire performance rating. Swapping a non-combustible covering such as slate for one that would behave quite differently in a fire is a trigger. Most coverings used on a house are comparable, but thatch, cedar shakes or an unusual membrane may not be.
Weight
The weight trigger has its own section below, because it is the one most likely to catch a change from one material to a different one. Remember that the three triggers are alternatives: any one of them is enough.
Area is the test people remember. Weight, structure and fire performance are the ones that catch people out.
Heavier coverings and the structural check
Approved Document A, which deals with structure, calls a rise of more than 15 per cent in roof load significant. The Planning Portal words the same idea as 15 per cent or more. The two differ right at the boundary, so if your new covering lands near that figure, ask building control rather than relying on either. Both sources agree on the consequence: the existing structure must be able to carry the increase.
Where it cannot, because members are overstressed or deflection is already visible, strengthening follows. The Planning Portal advises taking advice from a structural engineer or surveyor ahead of starting.
Where it bites in Stroud
Stone is the obvious case. Cotswold District Council's technical guidance records roughly 1,000 kg of stone slate on every 10 m² of roof. Laying stone where a lighter tile used to be, or natural stone where concrete tiles were, adds load. Going the other way reduces it, which is not a structural problem but can raise questions of appearance and consent on an older building.
We compare the weight of the old and the new covering per m² at survey stage, before any quote is written. If the difference is close to the line, we say that plainly and suggest building control confirm the position.
How the sign-off works through GBCP or an approver
If an application is needed, there are two routes. You can use the council's building control service, or a registered building control approver, a private firm registered with the Building Safety Regulator. The registered approver regime in England has applied since April 2024; the older term "approved inspector" is no longer used.
In Stroud District
The Gloucestershire Building Control Partnership, known as GBCP, runs the council's service. It is an arrangement between Stroud District Council and Gloucester City Council. Applications go through www.gbcpartners.co.uk, and the service can be reached on 01453 766321. The Stroud site says that where notice of an inspection arrives before 3pm on a weekday, the council will try to get an inspector out the following working day where it can.
Elsewhere nearby
Cheltenham and Tewkesbury share a service, Cheltenham and Tewkesbury Building Control. Forest of Dean District Council operates its own. Cotswold District Council has its own building regulations pages. Which body applies depends on where the property is, not on who is doing the work.
Whichever route you take, the pattern is the same: an application or notice before work starts, inspections at set stages, and a completion certificate at the end. Keep that certificate with the house papers, because a buyer's solicitor will ask for it.
What the body wants to see
An application is not a long form for a simple re-roof. Expect to describe the roof, the covering and its weight, the battens and underlay, how the ridge, hip and verge will be fixed, and what is happening to insulation and ventilation at the eaves. The more of that we have measured and photographed beforehand, the quicker the conversation goes, and the fewer surprises there are once the roof is open.
What it looks like on a real job
A typical full re-roof on a semi-detached house goes over the 50 per cent limit. So the sequence we follow is this.
- At the survey we measure the slopes and note the covering, battens and underlay, with photographs.
- We tell you whether the job is notifiable and what the application involves, including any insulation consequence.
- The application or notice is made to GBCP or your chosen approver before the strip begins.
- The building control body inspects at the stages it sets. Timber and insulation, once uncovered, are the usual points.
- On completion you receive the certificate or the formal sign-off from the body.
Records worth keeping
We photograph the roof before the strip, with the timbers bare, and again at completion. If an inspector cannot attend at the moment the rafters are exposed, those pictures show what was found. Keep them with the certificate.
Costs and timing
There is usually a building control fee, which is allowed for in your quote. We do not give a figure here because it varies by body and by job. Allow for the process in your timeline, and ask us to talk it through at the survey.
Planning permission and listed building consent are separate matters, and a listed home, or a property inside a conservation area, may need them in addition. The council's planning team will advise, and our signs guide includes what to photograph before you ring them.
Worked examples: which tests each job meets
Three common jobs show how the tests combine. They are illustrations, not rulings; building control decides each case.
Re-covering the rear slope of a semi
One slope is roughly half of a simple pitched roof, so the 50 per cent test is borderline and the survey measurement matters. If the covering is the same material and weight, the structure is untouched and the fire performance is the same, the area tests are the only ones in play. Close to the line, we ask GBCP rather than guess.
A full strip and re-cover in matching tiles
Every slope is renewed, so the 50 per cent limit is passed. The application applies even though the tiles look identical. Because the rafters are laid bare, the insulation rule in Part L also needs checking.
Natural slate replacing concrete tiles
Slate is usually lighter than concrete tile, so the weight trigger may not apply, but the whole roof is being renewed, so the area test does. A change from slate to something much heavier is the reverse and calls for a structural check.
In all three, the answer comes from measured areas and known weights, which is why the quote records them. Our materials guide compares the coverings and what each weighs.
Jobs that stay below the line
Plenty of roof work needs no application. Replacing a handful of slipped tiles, re-bedding a ridge, renewing a flashing or patching a valley all leave the roof share well below 50 per cent, and they do not change structure, weight or fire performance. The same is true of a like-for-like re-cover of one small slope.
Planning is a separate question. Section 55 of the 1990 planning Act excludes work that leaves the look of the outside essentially unaltered, so a re-cover in matching material is not usually something that needs planning permission. The exceptions are a listed building, and a conservation area where an Article 4 Direction applies. Stroud District has 41 conservation areas, with Article 4 Directions in five: two parts of Stroud itself, plus Wotton Under Edge, Frampton on Severn and Bisley, a short list worth checking against your address. The council's page is silent on whether roofs are covered, so ask its planning officers.
Even when no application is needed, the work still has to be done properly. Under BS 5534 the ridge, hip and verge are fixed mechanically, not left to mortar alone. Where we are unsure whether a job crosses a line, we ask GBCP and pass on what they tell us.