Plenty of owners planning a garage roof expect one of two answers: it is only a roof, so nothing is needed, or it is a building job, so everything is. The truth sits in between. Plenty of garage re-covering work needs no application at all. Other jobs, such as raising the roof, changing its structure or fitting a heavier covering, do need approval, and the difference is set out in the Planning Portal's guidance on re-roofing.
Its test is short enough to remember. Repairs and re-covering stay outside building control where under 25 per cent of the total building envelope and under 50 per cent of the roof is affected. Break either limit and approval is needed; so it is for structural changes, a covering with a very different fire rating, and one adding 15 per cent or more to the weight.
This guide takes you through each part, explains why attached and detached garages raise different questions, covers insulation, and says who to ask in Worthing and Adur. It is general information and not legal advice. Your building control body decides how the rules apply to your garage, so a short call before work starts is always the safest step.
The two limits that decide most garage jobs
The Planning Portal sets out two limits together, and both must be met for the no-application route. First, less than 25 per cent of the total building envelope must be affected. That envelope takes in every wall, the floor, the roof, and each window, door and rooflight. Second, less than 50 per cent of the roof must be affected. These are not interchangeable. A job can pass one test and fail the other, and it needs approval if it fails either.
Take a detached single garage that is a simple box. Replacing the entire roof covering means the whole roof is affected, so the second limit is passed. Whether the first is passed depends on how much of the whole building envelope that roof represents. On a small garage the roof is a large share of the envelope, which is why a full re-cover can tip the job over the line where the same work on a big house would not.
A common slip to avoid
The test is not that more than a quarter of the roof needs approval. It is a quarter of the building envelope and half of the roof. Mixing the two up is the most frequent mistake in online advice, and it changes the answer. A repair to a few sheets sits well under both limits. A whole new covering on a small garage may not.
Whatever the percentages, the Portal names three further triggers: structural alterations, a new covering with a markedly different fire performance, and added weight in the covering of 15 per cent or more. We look at each of those in the sections below, and at the point where approval turns into a practical application.
Attached or detached: what changes for a garage
The envelope in the 25 per cent test is that of the building being worked on. A garage that is part of the house, sharing a wall or a roofline with it, raises a question a stand-alone garage does not: is it measured as part of the whole house, or as a building in its own right? We do not guess. Ask the building control team how they treat your garage, and give them the facts they need to answer.
Tell them whether the garage is attached or detached, how it is built, whether there is a room above or beside it, whether it is heated or used as living space, and what you want to do to the roof. Those details settle which parts of the regulations are relevant, and a clear email gets a clear reply.
Garages that are not simple boxes
A garage with a habitable room above it is a very different building. The ceiling between has fire, sound and insulation implications, and the roof is the roof of a dwelling space. A garage being converted into a room, an office or a gym turns into a case with its own rules; our page on garage conversion roofs explains the roof side of that.
Many garages sit on a boundary or share a wall with next door, and the wall and roof edge may belong in part to a neighbour. That matters for access, for flashings and for the party wall rules that apply to work on a shared structure. Our page on shared garage roofs goes into it.
Finally, the roof may be one of several garages in a row, an arrangement you often find behind older terraces. Each owner's section still needs to meet the thresholds as a separate part of a longer structure. Ask building control how they would count it.
Structure, weight and fire performance of the new covering
These are the triggers that can require approval even for a small job. The first is structural alteration. Changing a flat roof for a pitched one, adding or removing beams, cutting openings for a rooflight or changing the way a roof bears on its walls are all structural. Our guide to converting a flat garage roof to pitched covers what that involves.
The second is weight. For weight, the Planning Portal's line is 15 per cent or more added to the covering. In Approved Document A, a loading increase of more than 15 per cent counts as significant, and strengthening or replacing a structure that cannot cope is a material alteration. The Portal also suggests that a structural engineer or surveyor look at replacement tiles that are much heavier or lighter.
Why precast and sheet garages need care
A concrete sectional garage has roof panels designed around their own weight, with a limited margin. Swapping lightweight sheets for tiles is the sort of change that adds weight quickly. Our page on concrete sectional garages explains the roof panels and the options. A corrugated roof replaced by a different sheet usually adds little, but not always, which is why corrugated garage roofs are surveyed before a covering is chosen.
Fire performance
The third trigger is the covering's performance in a fire. Approved Document B now describes roof coverings near compartment walls by a European class, after its 2025 amendments removed the national classes. In practice, a covering with a markedly different fire performance from its predecessor needs approval, and a garage close to a boundary or a house wall is where the question comes up. The maker's data sheet states the class.
Insulation and the thermal upgrade question
Re-covering can bring insulation rules into play. The Planning Portal's re-roofing page says you may be required to upgrade the thermal element, and Approved Document L Volume 1, for dwellings, counts a fresh waterproof layer over a flat deck as renovation of that part of the building. When more than 50 per cent of the element's surface is covered, or the whole job renovates more than 25 per cent of the external envelope, the complete element must be upgraded.
That volume is written for dwellings. Whether and how it reaches a garage depends on the building, its use and whether it is heated, so building control gives the ruling, not a roofer. If they do, Table 4.2 of Approved Document L sets 0.15 W/(m²·K) as the limit for roof elements that are new or replaced in an existing dwelling, and 2.2 for a rooflight. A lower U-value means less heat lost.
When it matters in practice
An unheated garage used for the car and the lawnmower is a different case from one used as a workshop with a heater. A garage that is being converted to a room will need the full set of insulation and ventilation details, and cold-roof ventilation has to be planned from the start. A single-ply EPDM roof over a well-insulated deck is a common way to meet an insulation requirement without raising the roof much; EPDM garage roofs are covered in their own guide.
A flat roof replacement is also the moment to look at the fall. IKO, citing the 2018 edition of BS 6229 (since revised), sets a design fall of 1:40 so the finished roof still reaches 1:80. That is workmanship rather than regulation, but a new roof that ponds is a new roof that fails early.
Where insulation goes in as part of other roof work, VAT is a separate matter, so ask how the quote treats it.
Applying, inspections and who does the checking
If an application is needed, you have two routes. The first is the council's own building control team. Adur and Worthing share one team, at the town hall in Chapel Road, with contact details on the councils' website. The second is a registered building control approver, a private firm on the Building Safety Regulator's register. Since 6 April 2024 that has been the proper term for the private route.
The councils say they now concentrate on statutory work and may not give design advice. They describe a nationwide shortage of inspectors qualified under the new regime, and the owner has to tell the team when particular stages of the work are reached. Fees carry VAT, except regularisation fees, and domestic charges are on the council's fees page.
Doing it in the right order
Apply before the work starts. An application made after the event is called regularisation, and parts of the roof may have to be opened so an officer can see inside. That takes longer than getting it right first time.
Where an application is needed, we walk you through the consent and look after the Building Regulations notification, so you are not left with the forms. Keep the paperwork anyway: a completion certificate is what a buyer's solicitor will want to see.
Good workmanship is not a substitute
A tradesperson being good at the work does not replace a building control application where one is required. If a roofer tells you nothing is needed, ask what the thresholds are and how they have been applied to your garage. The answer should refer to the envelope and the roof, not a single percentage.
Planning, scaffolding, wildlife and the neighbours
Building Regulations are one of three separate systems. Planning permission is another, and it asks whether the finished building looks acceptable. A straight like-for-like re-cover is seldom caught by it, because nothing about its outward appearance changes. Listed buildings and Article 4 areas are the caveats, and a conservation area means an extra check. Check with the Adur & Worthing planning team, or, if your garage lies inside the National Park, with the South Downs National Park Authority.
Party wall law is the third system. It applies when work touches a shared wall, and the neighbour must be served notice two months to a year before building starts. Do not assume that a neighbour who stays quiet has agreed. We do not give advice on the Act itself, but we flag it on the survey when your garage shares a wall.
Scaffolding and the pavement
Most garage roofs can be reached by ladder and platform, but where a scaffold must stand on the highway, a licence under section 169 of the Highways Act 1980 is needed from West Sussex County Council, or Brighton & Hove for sites in the city. The scaffold firm handles that application; the county expects 10 working days between applying and putting the scaffold up. That timing can hold a job up, so ask early.
Bats and birds
Tell us if you have seen bats or nesting birds around the garage, because the law protects both and disturbing them is easy during roof work.
Once surveyed, you get our written quote as one total figure, and it names the covering, the insulation and whether a building control application is needed. Our garage roof replacement page covers the wider choices. For a regulation question about your garage, send us its dimensions, how it is built, and photographs inside and out.
