Timber frame construction and fire risk during build

Timber frame fire risk during construction is not a Building Regulations problem. The completed building will meet Approved Document B like any other, with its plasterboard linings, cavity barriers and compartmentation in place. The risk sits in the weeks between erecting the frame and completing those linings, when a multi-storey structure of exposed softwood stands open to the weather with no fire resistance at all.

That exposure period is a health and safety and insurance matter, which is why developers are often surprised to find it discussed by a planning officer. The reason is simple: the mitigation involves separation distances, site layout, phasing and access for fire appliances, and all four of those are things a construction management plan condition can control.

Why construction phase fire risk reaches a planning officer

Three routes bring it into the planning process.

The first is neighbour amenity and safety. Where an exposed timber frame stands close to occupied housing, a school or a hospital, the fire and rescue authority or the council's own officers may comment, and the authority has an interest in how the risk is managed next to sensitive receptors.

The second is phasing on larger sites. A scheme that occupies the first phase while erecting the frame of the second has created an occupied building next to an unprotected structure, and the sequencing that avoids that is a layout and programme question rather than a construction detail.

The third is access and water supply. Fire appliance access routes, hardstandings and hydrant positions are fixed by the site layout, and a layout that works for the completed development may be unusable during the build.

None of that makes fire safety a planning consideration in the way the Building Regulations are. It means the practical mitigation shows up in planning documents, usually in a Construction Management Plan secured by condition.

Separation from existing buildings and boundaries

Separation is the primary control during the exposure period. The timber frame sector's own guidance sets out recommended separating distances between an exposed frame and neighbouring buildings or site boundaries, derived from the size and height of the structure being erected.

Where the recommended distance cannot be achieved, the recognised alternatives are:

• Build the boundary elevation in masonry or another non-combustible construction rather than in timber frame.
• Apply the fire-resisting lining to the boundary elevation as the frame goes up, rather than later in the programme, so the exposure period for that face is minimal.
• Erect a temporary fire-resisting screen or hoarding designed for the purpose.
• Phase the works so the exposed frame is never within the critical distance of an occupied building at the same time.
• Change the structural system on the constrained part of the site.

The first and last options are the ones that reach planning, because they change the external materials or the massing. A boundary elevation switched from render on timber frame to facing brick is a material change that may need agreeing with the authority, and it is better raised at application stage than as a late amendment.

Phasing, occupation and the exposed frame

The sequencing problem deserves separate attention because it is the one most often left until the sales programme is set.

Occupation of completed units is driven by cash flow. Frame erection on the next phase is driven by the build programme. Put those two together on a tight site and you can arrive at a situation where residents are living thirty metres from an unprotected five-storey timber structure, which no insurer and no fire and rescue officer will be comfortable with.

Resolving it needs a programme decision, not a drawing. The options are to complete the linings on each phase before starting the frame of the next, to build the phases in an order that keeps the exposed frame away from occupied units, or to use non-combustible construction on the elevations facing the occupied phase.

Say which one you are doing in the construction management plan. An authority asked to approve a phasing condition will accept a clear sequence and will resist a vague commitment to manage the interface.

Site fire plan, access and water supply

A construction phase fire plan is required under health and safety law rather than planning law. The Construction (Design and Management) Regulations 2015 place duties on the client, the principal designer and the principal contractor, and the published health and safety guidance on fire safety in construction sets out what the plan should cover. The Regulatory Reform (Fire Safety) Order 2005 also applies to construction sites.

What a planning officer needs from it is narrow:

1. The emergency vehicle access route through the site, with widths and turning provision, kept available throughout the build.
2. The position of hydrants or other water supplies for firefighting, and whether new hydrants are being provided.
3. The muster points and the escape routes for site operatives, where these interact with public footways.
4. The arrangements for liaison with neighbouring occupiers and with the fire and rescue service.
5. The hours and sequence of the works affecting those arrangements.

Water supply is worth checking early. Fire and rescue authorities have duties around securing water supplies for firefighting, and developers are frequently asked to provide hydrants to serve a new scheme. Finding out at groundworks stage that a hydrant main is needed is a familiar and avoidable delay, and it interacts with the service runs you have already designed.

Insurance-driven design changes

Insurers drive more of this than the planning system does. Contract works insurance for a timber frame project is priced against the exposure period, the separation achieved and the controls in place, and the recognised joint code of practice on fire prevention on construction sites is commonly a condition of cover above a contract value threshold.

That produces design changes which have to be reflected in the planning permission:

• A switch from timber frame to masonry or steel on part of the scheme.
• Non-combustible external wall construction on specific elevations.
• Sprinklers or other suppression where they were not previously proposed.
• Changes to the external material palette, which affects the approved elevations.

Each of those may need a non-material amendment, a variation of a materials condition, or in a significant case a fresh application. Build the insurance conversation into the pre-application programme so the structural decision is made before the elevations are approved rather than after.

Taller buildings bring the regulatory framework in directly. Restrictions on combustible materials in the external walls of relevant buildings apply under the Building Regulations, and the scope and height thresholds have been amended more than once, so check the current text. For buildings of 18 metres or more, or seven or more storeys, containing two or more dwellings, a Fire Statement is required at Planning Gateway One under Article 9A of the Development Management Procedure Order 2015. It must be prepared by someone with the necessary fire-engineering competence, and an AI-assisted draft is a starting point for that professional rather than a substitute.

The questions planners ask about engineered timber overlap heavily with this, and mass timber schemes and the questions planners ask covers the permanent-condition side of the same argument.

Where this sits in the construction management plan

Construction management plan conditions are usually drafted as a list of matters to be covered. Fire is often absent from that list, which is an opportunity rather than a gap: adding a short fire section makes the document more useful and heads off a later request.

Four paragraphs are enough. The structural system and the expected exposure period. The separation achieved to each boundary and occupied building, with a plan. The mitigation adopted where separation is short. And the emergency access and water supply arrangements, cross-referenced to the site layout drawing.

Keep it consistent with the other construction documents. Demolition and site clearance conditions often carry their own requirements, and the way asbestos surveys before demolition and what conditions cover are handled is a good model for how much detail a discharge submission actually needs.

Conditions and informatives to expect

Expect a pre-commencement condition requiring a construction management plan, a condition tying the development to approved materials, and on larger schemes a phasing condition.

Expect informatives rather than conditions on the fire side itself. An authority will often note that the developer must comply with health and safety law and should liaise with the fire and rescue service, which is a signpost rather than a requirement.

Two drafting points. Ask for the materials condition to allow for samples to be agreed rather than naming a product, so an insurance-driven substitution does not need a formal amendment. And where phasing is conditioned, define the phases on a plan with reference numbers, because a phasing condition without a plan is a dispute waiting to happen.

Browse the report types on PlanScope to see which construction stage documents a timber frame scheme is likely to need.

This is general guidance, not legal advice; check the current regulations and the position with your local planning authority, your insurer or a qualified fire engineer before relying on it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.