Timber frame and the fire questions asked at planning

Construction method is not, in general, a planning matter. How the walls are built is for Building Regulations and the Building Safety Regulator, and a case officer has no power to refuse a house because it has a timber frame. Even so, fire questions about timber and mass timber do arrive at planning stage, through three specific routes: the Fire Statement required for relevant buildings, external materials as a matter of appearance and regulation 7, and construction-phase fire risk controlled through a construction management condition.

If you are a self-builder putting up a two-storey timber frame house, almost none of this bites. If you are working on a block of flats, read on.

Where planning controls fire, and where it does not

Planning controls the use of land, the scale and siting of buildings, their external appearance and their relationship with neighbours and the highway. Fire performance of a wall build-up sits outside that.

Article 9A of the Town and Country Planning (Development Management Procedure) (England) Order 2015 is the exception that proves it. Applications for development involving one or more relevant buildings must be accompanied by a fire statement on the form published by the Secretary of State. A relevant building is one containing two or more dwellings or educational accommodation that is at least 18 metres in height or has at least seven storeys. The Health and Safety Executive, acting through the Building Safety Regulator, is a statutory consultee on those applications. That is Planning Gateway One.

The statement is deliberately about the things planning can influence: the siting and layout of the building, access and hard standing for fire service vehicles, the location of water supplies for firefighting, external wall construction in principle, and how the scheme allows for evacuation. A Fire Statement of this kind has to come from someone with the necessary fire engineering competence under the Building Safety Act 2022 framework, and a draft prepared any other way is a starting point for that person rather than a substitute for them.

The questions councils and consultees actually ask

For schemes below the Gateway One threshold, the fire questions that reach a planning file tend to come from the local fire and rescue authority as a consultee, or from a highways officer looking at access.

• Can a pump appliance get within the required distance of the dwelling entrances, and can it turn?
• Is there a hydrant within reach, and if not, who is paying for one?
• Where a private drive serves several houses, is it built to carry a 12.5 tonne appliance?
• On a tight urban plot, how close is combustible construction to the boundary during the build?

None of those are about whether the frame is timber. But they get asked more sharply when it is, because the fire officer knows the construction period is the risky window.

In London, policy D12 of the London Plan 2021 adds a fire safety requirement to major development, and boroughs ask for fire statements more widely than Article 9A alone requires. Check the borough's validation list rather than assuming the national threshold applies.

Height, and what regulation 7 does to a timber design

Regulation 7(2) of the Building Regulations 2010, as amended, requires materials which become part of an external wall, or of a specified attachment, to achieve European Class A2-s1, d0 or better on relevant buildings at or above 18 metres. The scope was extended in December 2022 to take in hotels, hostels and boarding houses.

Read that as written. It does not say cladding. It says materials which become part of an external wall, and that has been understood to reach structural elements within the external wall build-up. Cross-laminated timber forming the external wall of an 18 metre residential block is therefore a problem, whatever is hung on the front of it. Below 18 metres the restriction does not apply, which is why so many mass timber residential schemes in England stop at six or seven storeys with a non-combustible external wall line.

This matters at planning because it constrains the elevations. A scheme that shows timber cladding on a tall block, then meets regulation 7 by substituting a mineral board at technical design, arrives at discharge of conditions with a different building from the one that was approved. Resolve the materials strategy before the Design and Access Statement is written, and say in it which surfaces are combustible and which are not.

Construction-phase risk and the conditions that control it

A timber frame under construction is at its most vulnerable between erection and the fitting of plasterboard. Fire load is high, compartmentation does not yet exist and the site is open.

The insurance industry's Joint Code of Practice on fire prevention on construction sites is the reference document, and most contractors' policies require compliance on timber frame work. The Structural Timber Association publishes guidance on separating distances during construction, which categorises a build by floor area and distance to the site boundary and to other occupied buildings, and sets out the controls each category needs.

Councils rarely impose any of this directly. What they do impose is a condition requiring a construction management plan, and on a constrained site that plan is the right place to deal with hot works permits, site security out of hours, temporary water supplies, phased plasterboard fixing and separation from the boundary. Drafting it properly at application stage is faster than arguing about it after committee.

Illustrative example. A four-storey timber frame block of 14 flats sits 6 metres from a terrace of Victorian houses across a side road. The fire and rescue consultee raises separating distance during construction. The applicant offers a condition requiring a construction management plan prepared in line with the Joint Code, phased erection with plasterboard following within an agreed period, no hot works, and a fire marshal during erection. The condition is agreed and the objection is withdrawn. The detail here is illustrative.

Insurance, warranty and lending, which shape the scheme before planning does

This is the part self-builders discover late. Structural warranty providers and building insurers each apply their own acceptance rules to timber frame and mass timber, and those rules are commercial rather than statutory. A provider may require a particular erection sequence, a specified separating distance, or a third-party review of the fire strategy. Lenders follow the warranty.

The practical consequence is that the structural decision should be tested with the warranty provider and the insurer before the planning application fixes the massing and the elevations, because a late switch to masonry changes wall thicknesses, window reveals and floor-to-floor heights. Escape and fabric can pull against each other in the same way on older buildings, as anyone who has dealt with fire safety in a listed building will recognise.

What to put in the application, and what to leave out

State the construction method plainly in the design statement and deal with the three planning-relevant points: appliance access and water supply, the external wall materials and their fire classification, and construction-phase management secured by condition.

Do not offer a full fire engineering case at planning for a building below the Gateway One threshold. It invites scrutiny of matters the council cannot control and it will not be read by anyone qualified to judge it. Where the building is a relevant building, the fire statement is mandatory and a supporting Fire Safety Strategy to BS 9991 is fire engineering work that has to be authored by a competent fire engineer.

Be accurate about what is fixed and what is indicative. A planning submission that promises a specific wall build-up is making a commitment it may not be able to keep after Gateway Two. The three constraints that shape tall mass timber residential schemes are worth reading before you settle the storey count.

This is general guidance, not legal advice. Check the position with your local planning authority, the Building Safety Regulator or a qualified professional before relying on it.

Browse the PlanScope report types to see which documents a framed residential scheme is likely to need.

PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.