The short answer
A commercial re-roof does not normally need Building Regulations approval for simple repairs, but approval can apply once the job is large, the new covering is far heavier, or the insulation must be improved. The Planning Portal gives thresholds written for houses. A shop, factory or school is a question for your building control body, so ask before work starts.
Repair, re-cover and re-roof are different things
Many clients assume a roof is simply a roof. In regulatory terms it is a mix of waterproofing, structure, insulation and fire performance, and a change to one part can bring the others in. The rules draw a line between maintenance and renewal. Patching a leak, replacing a few sheets or re-seaming a membrane is upkeep. Stripping a covering to the deck and laying a new one is a bigger act, and that is where approval starts to bite.
The Planning Portal publishes thresholds for dwellings. Approval for repairs and re-covering is normally not required when under 25 per cent of the whole building envelope is touched and under 50 per cent of the roof itself. Past those points approval is in play and the thermal element, the part of the construction that holds heat in, may need upgrading. The Portal writes its examples around houses.
A commercial building is not a house, so we do not tell a business client that a house figure is safe to lean on. The sensible course is to describe the planned work to your building control body, which is either B&NES building control or a registered building control approver, and ask whether it is notifiable. We can set the scope out clearly so the answer comes back quickly.
Weight, structure and fire
A change in weight can pull a re-roof into the rules even when the area is modest. According to the Planning Portal, approval is needed if the replacement covering weighs 15 per cent or more beyond the old one, since the structure beneath may need checking. Swapping light metal sheet for a heavy tiled or ballasted system is the sort of change that does it.
Going lighter deserves thought as well. A much lighter covering alters how the roof copes with wind, because there is less dead weight to resist uplift. On a large, shallow commercial roof, wind uplift is a design question in its own right.
Fire performance of the covering, the placing of rooflights and the distance to the site boundary are further things building control weighs when a roof is renewed. Those depend on the building, its use and its position, and cannot be settled in general terms, so we gather the details on the survey and pass them on. They are the reason to talk to building control before materials are ordered.
Thermal upgrades on commercial roofs
When a roof is largely renewed, its insulation often has to improve alongside. On a flat commercial roof that usually points to a warm-deck build-up, in which insulation is laid over the structural deck and under the waterproof layer, keeping the deck warm so condensation gets little opportunity to form within the construction.
This is where cost climbs, and a major reason why a re-roof quotation can look very different from a simple re-cover quotation. Our page on commercial roof energy performance explains how insulation, rooflights and U-values relate, and the commercial roof cost page covers price drivers.
An overlay, where a new membrane goes over the old covering, is sometimes suggested to avoid a full strip. It has limits of its own, including added weight and wet insulation left underneath, and it does not remove the question of whether the job is notifiable.
Listed buildings, conservation areas and other consents
Building Regulations are one set of rules among several. A listed building needs listed building consent for work that touches its character, and in Bath that consent comes from B&NES Council. Consent of that kind sits apart from planning permission, and unauthorised work is a criminal matter. B&NES planning should be asked first.
Roughly half of Bath sits inside the city-wide conservation area, and the entire city is a World Heritage Site, so a roof visible from the street can raise further questions. Outside Bath the right council depends on the town. Our page on listed commercial roofs goes further.
Asbestos is a different matter again. Where an old roof carries asbestos cement sheeting, the method of removal affects which rules apply. See asbestos on an industrial roof.
What to do before the work starts
Gather what you already hold before you ask: the original drawings if they exist, the existing specification, any previous approval notices and a note of past leaks. They make the conversation with building control shorter and the answer more reliable. Begin by writing down the plan: how much of the roof, which covering, whether insulation changes and whether rooflights move. Put that to your building control body in writing. If it is notifiable, an application goes in before work begins, and a registered building control approver or the council inspects as the job proceeds.
Timing matters because approval takes time, and a re-roof is also governed by season. Some systems cannot be laid in cold, damp weather, so the programme must allow for both. Our answer on commercial roofing in winter explains which systems cope.
Where work is notifiable, we explain the consent position and deal with the paperwork. For a ruling on your particular building, building control is the body to ask, since the answer is theirs to give. Our free survey comes first. The written fixed price afterwards flags any part of the scope that could bring approval into play. Our wider offer for businesses is under commercial roofing.
