Changes to Approved Document B could have profound implications for timber construction and the UK’s net zero targets. Andrew Orriss, Chief Executive of the Structural Timber Association (STA) provides some critical considerations.
THE GOVERNMENT has been consulting on changes to Approved Document B, the fire safety guidance that sits alongside the Building Regulations. The consultation was run jointly by the Building Safety Regulator, the Health and Safety Executive, and the Ministry of Housing, Communities and Local Government. It applied to England and closed on 1 July, so it is no longer open for responses.
Before getting into the detail, it is worth clearing up a point that keeps coming up in discussions about this consultation, including in the STA’s own response. Approved Document B is not the regulation. It is statutory guidance on ways to meet the regulation. The Building Regulations set the legal requirements. Approved Document B – like the other Approved Documents – sets out one way (not the only way) of satisfying them. That distinction matters, because much of the anxiety around this consultation comes from people reading the guidance as if it carries the force of law. It doesn’t. Alternative routes to compliance, using recognised standards such as BS 9991, BS 9999 or BS 7974, are equally valid.
11 metre thresholds
This review didn’t come from nowhere. The Grenfell Tower Inquiry Phase 2 report recommended that Approved Document B be kept under continuous review, and this set of changes is the latest step in that process. The areas covered include cavity barriers, rules for work on existing buildings, external wall systems, and a proposed height threshold above which buildings with combustible structural elements, including timber, would need to look beyond Approved Document B for their fire strategy.
That last point, the 11m threshold, is where most of the industry attention has landed. The government’s reasoning is that the guidance in its current form was written with reference to construction methods and materials from decades ago, before combustible structure and insulation were used at the scale, they are today, and that taller or more complex buildings need a different approach. The STA does not disagree with the principle of a threshold. Its response supports the idea that there should be a point above which Approved Document B guidance no longer applies on its own.
Where it takes issue is with how the threshold is drawn. A single cut-off at 11m, applied the same way to a four-storey timber frame house and office block or school, does not reflect how different those buildings are actually used. The STA response includes requests for more categories: different treatment for residential and non-residential buildings, and clearer thinking about long-standing building types, such as exposed oak frame structures, that could otherwise be caught by wording that presumably wasn’t really aimed at them.
Clarity required
The other significant concern is about clarity, not intent. Some of the drafting, if read literally, could restrict the use of OSB sheathing and common insulation types in ordinary low-rise timber frame housing. The STA doesn’t believe that is the goal of the consultation. But guidance will be read by people who are not fire engineers, and if the wording allows for that reading, it will get read that way project designers and building control officers. The STA’s request is straightforward: say what is intended clearly, and where guidance doesn’t yet exist for a particular building type or method, say that too, so that people know when they need to bring in a specialist rather than guessing.
None of this is an argument against timber construction. The STA has said plainly that it supports what government is trying to do here. Reviewing fire safety guidance after the Grenfell Inquiry is right, and the Building Safety Regulator (BSR) has stated that this consultation is in line with the Timber in Construction Roadmap, which backs timber use to cut embodied carbon. The STA doesn’t dispute that goal. Its point is that the claim only holds if the detail gets fixed. As currently drafted, several of the changes would make it harder to build in timber, not easier, so unless the BSR clarifies its intent and amends the proposals, the guidance won’t end up matching the Roadmap it says it supports.
The STA will keep trying to liaise with the Building Safety Regulator now that the consultation has closed and will, if necessary, work with the regulator and other stakeholders to develop further guidance for Industry where this is required. If low-rise timbe frame dwellings require guidance outside of Approved Document B to demonstrate compliance without a significant shift in product used, then that would be disappointing.
