A commercial roof is a regulated part of the building, not just a weatherproof lid. When you strip and re-cover one, three separate bodies of rules can come into play: the energy requirements of Part L, the structural limits of Part A, and the fire provisions of Part B. Alongside them sit health and safety duties on asbestos and work at height, which are enforced by a different regulator. This guide describes how those pieces fit together for a business roof in England, so that you ask the right questions of your contractor and your building control body before a scaffold goes up. It is general information, and your building control body has the final say on your project.
When a re-roof needs a building control application
Most owners assume a like-for-like re-covering is exempt. Sometimes it is. The Planning Portal sets a two-part test: ordinary repairs and re-covering are usually left alone by building control while the work touches under a quarter of the whole building envelope and under half of the roof. Both conditions have to be met, and the figures are 25% and 50%. The envelope is every external surface of the building, including walls, floor and roof, so a large single-storey warehouse with a small roof-to-wall ratio can pass the first test easily and still fail the second.
Once the work goes beyond that threshold, you need approval, and the insulation across the entire roof can be made to meet current standards, not just the area you are touching. That is the point at which a straightforward patch-and-repair budget can double. It is why we ask early how much of the roof you want done and over what period. Phasing a job in two stages to stay under a threshold can look neat on paper, but a building control body may treat connected stages as one project, so raise it with them before you plan around it.
You can apply through your council's building control team or through a registered building control approver, which is the title private building control providers have used since April 2024. Where the work is notifiable, we handle the Building Regulations side for our customers. If you are unsure of the local position, the planning and building control pages of your council, for example Basingstoke and Deane Borough Council, are the place to start.
Plan for the paperwork as well as the roof. A building control body will want to see the specification before work starts: the covering, the insulation product and thickness, and any structural check. Inspections happen at set stages, and a completion certificate follows when they are satisfied. Cheap shortcuts here come back later, because a missing certificate can hold up a sale, a lease renewal or an insurance claim on the roof. Listed buildings and conservation areas add another layer, since changes to materials or appearance may need consent, so check with the council's conservation officer before choosing a different covering.
If your building is part of a larger estate, the roof may also be subject to the freeholder's consent and a managing agent's approved-contractor rules. Ask for those in writing at the start, so that the survey, quote and programme are drawn up against the same requirements.
Part L: the roof as a thermal element
Approved Document L for non-domestic buildings treats a roof as a thermal element. That means that when you renovate a substantial part of it, the energy rules expect the insulation to be improved as part of the work, not left as it was. In practice, a new waterproof layer on a tired roof is the best moment to add insulation, because the old covering is already off and the cost of reaching the deck is already spent.
The design consequences are physical and specific. Thicker insulation lifts the surface of the roof, so upstands at the walls, rooflight kerbs and plant bases must be raised to keep the same weather protection above the new surface. Outlets and gutters may need to be reset. A flat roof needs falls so water leaves the surface, and tapered insulation boards build those falls into the system. Where the existing roof is a profiled metal sheet, the build-up of liner, spacers and insulation is a specified assembly that must be completed as designed, because gaps or compressed insulation at fixings leave cold bridges and condensation. Part L also covers air tightness and thermal bridging at junctions, so detailing at eaves, verges and abutments is not a matter for improvisation on site.
The cost effect is substantial, which is why we have given it its own section in our guide to commercial roof replacement cost. We would rather tell you at survey that your roof will need an insulation upgrade than have it surface as a variation halfway through the job.
Part A: weight, wind and the structure underneath
Part A, the structural part of the regulations, matters whenever the new covering is heavier than the old one. Where the new covering weighs 15% or more above the old, approval is needed, and the frame carrying it may have to be strengthened. On an industrial unit, the arithmetic is rarely obvious. A lightweight single skin of profiled steel on purlins can be much lighter than a double-skin insulated panel system, and a built-up ballasted flat roof adds weight again with its stone or paving.
The same check applies to overcladding. Fixing a new sheeted layer over the old roof adds a second covering and its supporting spacers to a structure that was designed for one, and the existing purlins, rafters or trusses have to take it. Our guide to commercial roof overcladding covers how that decision is made. Where the structure is corroded, undersized or has already been modified for plant or solar, a structural engineer's input before the job is a sensible spend, and building control will often ask for the calculation anyway.
Part B: fire, boundaries and compartment lines
Approved Document B deals with fire safety, and two parts of it touch a re-roof. The first is external fire spread: roof coverings are classified by how they perform when exposed to fire from outside, and the classification restricts how close to a boundary a roof of a given type may be. A building near a neighbour's boundary may therefore be limited in the coverings it can use, and the product data sheet should state its classification. The second is internal fire spread: the roof structure can pass through or sit over compartment walls, and the fire resistance of that wall has to be maintained where it meets the roof. When a new covering or new insulation goes in, the fire stopping at the head of a compartment wall must be reinstated, not covered over.
Rooflights deserve a mention because they weaken a roof's fire performance, and rules on their position and area relative to boundaries apply. Plastic rooflights near a boundary or a compartment line are not a place to substitute products casually. Replacement units should match the performance of what they replace, or better, and the manufacturer's evidence should be on file. A fire strategy or a fire risk assessment, which a responsible person for a business premises must hold, will identify these lines, so ask for it before you specify materials.
Asbestos and work at height: the duties outside the Building Regulations
Two sets of duties govern how the work is done, whatever building control decides. First, asbestos. Under the Control of Asbestos Regulations 2012, the person in control of a non-domestic building has a duty to manage asbestos, which starts with knowing whether it is there. Asbestos cement sheets are common on industrial roofs built before the material was banned. The HSE says that removing asbestos cement sheets carefully without breaking them is non-licensed work, but it becomes notifiable non-licensed work if the material will be substantially broken up. A risk assessment, controls and trained workers are always needed, and overlaying is sometimes an alternative. Our guide to asbestos roofs on commercial buildings goes through the options. Official guidance is on the HSE's non-licensed work page.
Second, work at height. The Work at Height Regulations 2005 apply to every roof job, and fragile roofs are one of the commonest causes of serious falls in construction. Old rooflights, fibre-cement sheets and deteriorated metal panels can look solid and fail underfoot. Edge protection, covers, nets and safe access are part of the planning, and a contractor who does not mention them has not planned the job. We cover that side in our guide to fragile roof safety.
What to settle before work starts
A short checklist helps owners and managers, and it turns a regulation question into a set of documents:
- Which part of the roof is being renewed, and does it pass the Planning Portal threshold?
- Is an insulation upgrade required, and which product and thickness will meet it?
- Is the new covering more than 15% heavier than the old one, and has the structure been checked?
- What is the fire classification of the covering and rooflights, and are there boundaries or compartment walls to respect?
- Has the roof been surveyed for asbestos, and is the removal method agreed?
- How will people be kept safe at height and on the ground?
Keep the answers together with the building control decision notice or completion certificate. They matter when you sell, let or insure the building, and a buyer's solicitor will ask for them.
How we handle it
We begin with a free survey of the roof, with photographs, and the report says plainly whether we think the work will need approval and why. You then get a fixed written quote that includes any insulation upgrade the rules require. Where an application is needed we look after it with building control, and when we leave, the roof area is left tidy with the old material gone. A written 10-year workmanship guarantee backs what we fit. Our commercial roofing in Basingstoke page describes the systems we work on, and you can reach us on 01256 213956 or by WhatsApp with a few photos of the roof.
