BR18 and the roof: what the Building Regulations require

As a roofer you work every day within the frameworks that building regulations BR18 have set. You don't need to know the paragraphs by heart like a building administrator but you must know what requirements apply to roofing — because your work is ultimately what must meet them and it is often you the customer asks.

§Fire: what does BROOF(t2) mean?

BR18 requires that roof coverings are fire-appropriate. On far most buildings, this means that roof covering must be at least classified BROOF(t2). The classification comes from the European system and means that the roof covering has been tested against flying embers — that is, glowing embers and burning particles landing on the roof from a nearby fire combined with wind. A BROOF(t2)-approved roof covering reduces the risk that the fire ignites the roof and spreads across the surface. Modern roofing systems from established manufacturers are supplied as documented BROOF(t2) solutions — but only when the entire build-up, including substrate and insulation, matches the tested build-up.

§Moisture: the roof must protect the structure

BR18's moisture requirements basically state that buildings must be designed and built so that water and moisture do not cause damage or health problems — neither during construction nor during operation. For the roof, this means that the roof covering must be tight against rain and meltwater, that the construction must be able to handle the moisture naturally transported through it, and that there must be control of the vapour barrier and ventilation in the overall build-up. The roofer's membrane work is the outermost line of defense in the moisture strategy.

§Drainage: water must go away

The regulation requires that roof water is drained away from the building, typically via gutters, roof drains and downpipes to the drainage system. On flat and low-slope roofs it is in practice the fall and drain placement that determines whether the requirement is met: the industry's recommendation – as known from the earlier TOR instructions and today continued in manufacturers' instructions – is a fall of 1:40 on new roofs, while as low as 1:100 has been considered an absolute minimum, which the industry however advises against, because even small construction inaccuracies can then cause standing water.

§The details bear the evidence

BR18 is a function-based regulation: it says what the building must be able to do, not exactly how you do it. The path from functional requirements to concrete implementation goes through guidance — manufacturers' assembly instructions, industry guidelines and general technical common knowledge like BUILD/SBi guidance. When you follow a recognized guidance, you simultaneously have documentation that the work has been carried out in a skilled manner. That is invaluable if a dispute or insurance claim later arises.

• 01Know the specific roof construction before you start — it is part of the building case documentation.
• 02Never deviate from the designed structure without having it clarified in writing with the site manager.
• 03Take pictures of details before they are covered — coverings, penetrations, and connections at roof drains.
• 04Save delivery notes and datasheets so materials can be traced to the approved system solution.

For the apprentice the rules can seem like distant law but they quickly become concrete: The day a customer asks whether the new tar paper roof can lie so close to the neighbour's house or a site manager asks for documentation of the fire class it is the roofer with a handle on BR18 who appears professional. The rules are not an opponent — they are the trade's backing.