Fibreglass (GRP) flat roofs are commonly used throughout the UK because they are durable, seamless and low-maintenance. However, when you are renovating a roof or specifying a new build, above all the marketing statements, there is a question that matters most: does this GRP system comply with current UK fire regulations? This guide explains what Approved Document B says about roofs, how classifications like BROOF(t4) operate and what to check when selecting a GRP roofing system. What Building Regulations say about roofs Fire performance of roofs in England and Wales to comply with fire safety are based on the Requirement B4 of the Building Regulations 2010. Such regulations include the spread of fire across a roof and between buildings. Further information is contained in Approved Document B (Fire safety), Volumes 1 and 2, published on GOV.UK. In Approved Document B, the noteworthy points, as concerns roof coverings, are: Roofs must resist the spread of flame across the surface when exposed to fire from outside They must also limit fire penetration through the roof build-up The higher the fire performance, the fewer restrictions there are on distance to the boundary and the easier it is to use the roof on larger buildings Historically the UK used national classes from BS 476-3 (e.g. AA, AB). Current guidance shifts designers towards European classifications under BS EN 13501-5, and recent updates phase out many national classes so everything is aligned with EN standards. EN 13501-5 and why BROOF(t4) matters Under BS EN 13501-5, roof build-ups are given external fire performance classes: BROOF(t4) – highest external fire performance CROOF(t4), DROOF(t4), EROOF(t4), FROOF(t4) – progressively lower performance The "t4" refers to Test 4 in CEN/TS 1187, a severe scenario that combines burning brands, wind and intense radiant heat. The test measures both flame spread over the roof surface and fire penetration through the full build-up. A roof that achieves BROOF(t4) is generally treated in Approved Document B as "unrestricted" for external fire spread. In practice, that usually means it can be used: Close to or on the boundary On a wide range of building types and sizes Without extra limitations beyond the rest of the fire strategy For modern flat roofs, BROOF(t4) is therefore the benchmark most specifiers and building control bodies look for. How this applies to GRP roofing systems GRP itself is only one part of the story. What is tested and classified is the complete roof system, typically including: Deck (OSB3, plywood, concrete, etc.) Any insulation and vapour control layer GRP laminate Fire-retardant GRP topcoat or coating Reputable GRP manufacturers provide systems, not just resins, that have been tested to BS EN 13501-5 or, for older certificates, BS 476-3. Many of these GRP systems are marketed specifically as BROOF(t4)-compliant liquid roofs when installed on the deck and insulation build-ups used in their test reports. The crucial point is that you cannot assume "any GRP roof" is BROOF(t4). The build-up must match the tested specification. Change the insulation, increase the thickness or switch decks and you may no longer be using the certified system. Compliance checklist for GRP flat roofs When assessing the fire resistance of a GRP roof, use this quick checklist: Ask for proof of classification Request a current classification report or certificate showing the system tested to BS EN 13501-5 with a rating of BROOF(t4) where required. Match the build-up to the test Confirm that the deck type, insulation type and thickness, vapour control layer and GRP specification on your project mirror the tested build-up. If not, speak to the manufacturer or a fire engineer. Check distance to the boundary Approved Document B sets minimum roof-to-boundary distances based on the fire class and building use. Using a BROOF(t4) system gives the most flexibility in tight urban sites. Differentiate external performance from structural fire resistance EN 13501-5 focuses on fire from outside. Structural fire resistance (load-bearing capacity in a fire) is covered separately under other parts of the regulations and must also be satisfied. Adding a green roof? According to government-funded research it has been demonstrated that when the waterproofing beneath a green roof is AA or BROOF(t4) a well-designed green roof with a small amount of organic material and appropriate depth will be able to maintain good fire performance. Before making any decisions on the design of your building or the shape of the roof, always look at the latest Fire safety: Approved Document B on GOV.UK and discuss with Building Control at the very first opportunity.. Getting GRP materials that support compliance Apex Fibreglass Roofing Supplies is a company that provides full fibreglass roofing systems. We provide you with the resins, glass matting, topcoats and trims to construct powerful GRP flat roofs that can withstand the British weather. A properly defined and tested GRP system combined with quality materials and professional installation would produce a flat roof that will last, keep the water out, and comply with the current rules of the UK fire safety. When you are thinking of a new GRP flat roof, or even a renewal of a roof that you already have, the GRP kits of Apex Fibreglass Roofing Supplies is an easy place to start. Disclaimer: The paper is just a brief overview. On GOV.UK, the current Approved Document on your particular project is always available and the reports on the official fire classification of the GRP system used.
