Plenty of homeowners hear two opposite things about a new roof. One roofer says it is a straight swap and nobody needs telling. Another says building control must approve every tile. Neither is quite right, because the rules are built around the share of the house you change and what the new covering does, not around the word re-roof.
Three things settle the answer. The first is the proportion of the roof, and of the whole outer shell of the house, that you renew. The second is whether the replacement covering weighs more than the old one or would behave differently if fire reached it. The third is the energy standard in Approved Document L, which can bring insulation into a job that began as a tile swap. Councils can also word their own rules differently, and Crawley does. This guide takes each in turn and ends with who signs the work off. It is general information, not legal advice, so your building control body is the one to give a final ruling on your address.
The Planning Portal's two-part test
The best-known national guide comes from the Planning Portal. It says you can normally go ahead without a building control application only if "Less than 25 per cent of the total 'building envelope'" is affected, and "Less than 50 per cent of the roof is affected." Read those as a pair. Both have to be true together before the exemption holds, so passing one test and failing the other still means you ask building control.
What counts as the building envelope?
The envelope is the whole outer shell of the house. That means the walls, the floor, the roof, the windows, the doors, the roof windows and the rooflights together. On a small terraced house the roof is a big slice of that shell, while on a large detached house one slope may be a modest slice. That is why two jobs that look identical from the street can fall on different sides of the line.
Does a single slope pass or fail?
It depends on the house. Re-covering one slope of a simple two-slope roof touches about half of it, which sits right at the edge of the second test. Re-covering both slopes, or a roof with several sections and a rear extension, plainly crosses it. We work out the percentages from the measurements taken at the survey and tell you where your roof sits. Then we confirm the position with building control before work begins, not afterwards, because a stripped roof is a poor place to start a debate.
The test never excuses poor work. Even where no application is needed, new work should still meet the standards, which is why modern fixings are used on tiles rather than the habits of the original builders.
Heavier coverings and fire performance
The Planning Portal names two situations where approval is needed whatever the size of the job. The first is a replacement that adds at least 15 per cent to what the covering weighs. The second is a covering that would perform in a way "significantly different" to the old one if there were a fire.
When does weight become a problem?
Roof timbers are sized for a particular load. Moving from thin slate to thicker, denser concrete tiles adds weight, and the rafters, purlins and walls below must carry it. Approved Document A, the structural volume, calls a rise in roof loading of more than 15% a significant change. The two documents word the threshold slightly differently, with 15 per cent or more in one and more than 15% in the other, so we quote whichever we mean. The Planning Portal advises having the structure assessed by an engineer or surveyor before the work starts, and that is sensible for any swap where the weight is not obviously the same.
Where does fire performance come in?
Coverings are tested for how they behave when fire reaches them from outside the house. A switch to a different family of material, such as a single-ply membrane in place of tile or slate, can change that result. Matching like for like keeps you well inside the exemption, while a change of material is the moment to ask. If you are weighing such a change, our page on replacing a slate roof with tiles shows what to check on the weight side before you pick a product, and we put the old and new weights side by side in the survey notes.
The Part L thermal upgrade on a re-roof
Approved Document L is the part of the Building Regulations on saving fuel and power. For houses in England, the 2021 edition with its 2023 amendments took effect on 15 June 2022. It rates a roof by its U-value, the rate at which heat escapes through each square metre for every degree of difference between inside and outside. A lower number means a better roof, and good insulation produces a low number.
When does the roof have to be upgraded?
The document calls it a major renovation when the work reaches beyond one quarter of the outer envelope area. It also asks for an element such as the roof to be upgraded when more than 50% of that element's surface is renovated. Whether a particular tile swap counts as renovation is a question for your building control body, because it turns on how the roof is built. Where it does count, insulation in the roof is what delivers the upgrade.
Which figures apply?
Table 4.3 deals with existing elements under renovation and gives a roof threshold of 0.35 and an improved value of 0.16 W/(m²·K). Table 4.2 deals with new or replacement elements and gives 0.15 for a roof. Paragraph 4.13 offers relief: if Table 4.3 cannot be achieved sensibly, or insulating to that level would take longer than 15 years to pay back, you aim for the lowest value that is feasible and does pay back in that time.
The 2026 edition takes effect on 24 March 2027 for most work. Its tables become 3.2 and 3.3, with the 15-year payback test sitting at paragraph 3.14. Until that date, the 2021 edition is the one in use.
What Crawley and nearby councils say
Local wording can be stricter than the national guide, so it pays to know which council handles your address. Crawley Building Control, which runs the Local Authority Building Control service for the borough council, includes "repairing or replacing more than 25%" of a roof's surface among the work needing its approval. Crawley words the threshold its own way, quite unlike the Planning Portal test, and on larger Crawley re-roofs we check with them rather than lean on the national figures.
Who handles building control around Crawley?
All building control work in the borough is done by Crawley Building Control. Horsham District Council trades its service as Sussex Building Control, and Mid Sussex District Council runs a service of its own. In Surrey, the borough and district councils of Reigate and Banstead, Tandridge and Mole Valley share one team, the Southern Building Control Partnership. Other councils in our area have their own arrangements, and we check the right one for your address when we survey the roof.
Can a private body do the job instead?
Yes. You can use a registered building control approver instead of the council, and the registration rules started on 6 April 2024. Private approvers were around before then, so what is new is the register, not the option. Whichever route you take, it is that body, rather than the roofer or the tile maker, that rules on the finished roof. Appoint it early, since inspections can fall during the work and not only at the end, and tell the roofer which one you have chosen.
Planning permission: a different system
Planning permission and Building Regulations have separate decision makers and separate tests. A like-for-like re-roof usually falls outside planning control, because section 55(2)(a) of the Town and Country Planning Act 1990 does not regard works that keep a building's outward look much as before as development at all. A new roof that looks the same is therefore a building control matter, not a planning one.
When can planning still be involved?
Anything that changes the look of the building can bring planning in. Moving from slate to a visibly different tile, adding roof windows, raising the ridge or altering the pitch are all changes to describe to the council. A listed house needs listed building consent for any alteration that touches its character, even one that seems small. A conservation area counts as article 2(3) land, where some permitted development rights are narrower. For Crawley addresses, the planning team at Crawley Borough Council can say what applies, and for other places the right council is named on its website.
Where can I read about the special cases?
Our page on re-roofing in a conservation area covers one of those cases in full, and a listed house needs the same care. Our roof replacement page sets out the whole job from survey to sign-off. When you talk to the council, keep the two ideas separate. Planners look at appearance. Building control looks at structure, safety and the energy performance of what is built, and a green light from one never stands in for the other.
Paperwork, sign-off and what to settle first
A re-roof can end with a few documents, and a buyer's solicitor may ask for them many years later. If an application was needed, ask building control for written confirmation that the work was accepted, and keep it with your deeds. Our page on the building control certificate for a new roof goes through what to ask for.
Which questions should you put to a roofer?
Ask who deals with building control, you or the roofer, and whether the job needs an application at all. Ask what the new covering weighs next to the old one, and whether anybody has looked at the roof timbers for that change. Ask whether insulation is part of the plan and which U-value it is designed to reach. Check that the quote is one total price and states if scaffold and VAT are included. The government gives VAT at 20% as the standard rate.
What should you send us?
Front and rear photos of the roof help most, together with the decade the house dates from and any papers from earlier roof work or loft conversions. Mention a listed building, a conservation area or a block of flats if one applies. During the survey we take measurements of every slope, note the covering and the loft insulation, and say which of the tests above look likely to apply. The first thing we then do is put those answers to your building control body, so the single written price rests on the route it confirms.
Part of our Roof Replacement & New Roofs in Crawley
Re-roofing and the regulations
Can I re-roof with the same tiles and skip building control?
Possibly, if under 25 per cent of the envelope and under 50 per cent of the roof is affected, with a covering that is no heavier and behaves the same in a fire. That is the Planning Portal test. Crawley Building Control words its rule differently, so ask your council before work begins.
Is a new roof exempt from the Part L insulation rules?
Not automatically. Approved Document L treats work above set shares of the envelope and of an element as renovation, which brings a thermal standard with it. If the full upgrade cannot be reached, or repaid within 15 years, a lower feasible figure may apply. Your building control body confirms the route.
Does a heavier roof covering need approval?
The Planning Portal says approval is needed when a replacement covering adds 15 per cent or more to the covering's weight, and it also recommends structural advice first. Ask your roofer to put the weight of each covering in writing before you agree to the job, so the comparison is on paper.
