About 500 fires occur in England every day.  Detailed data is recorded about all incidents attended by the fire and rescue services in England. Fire statistics are collected and collated each year, recording fire incidents, their causes, spread and consequences for all fires and all construction types . Fire brigades and others investigate some fires in more detail to learn and inform the review of effectiveness of fire safety provisions.

Every building has voids, cavities and service and installation shafts as part of its construction. Fire can spread unnoticed in these spaces away from direct view, circumventing compartmentation and other fire safety measures within a building. Fire and smoke can spread rapidly in these concealed spaces and pose risk to life of occupants and fire-fighters as well as widespread damage.

The management of the uncontrolled spread of fire and smoke relies on cavity barriers and fire stops where there are joints and penetrations between building elements and openings at interfaces. Construction tolerances and shrinkage, due to timber elements drying out over time, can also cause gaps which need to be managed.

In the UK, building regulations provide requirements and guidance on the performance expectations of constructional features preventing unseen fire spread in concealed spaces.

• At the edges of cavities
• Around openings (windows, doors)
• At exit and entry points of services
• At the junction between any external cavity wall and every compartment floor and compartment wall
• At the junction between an internal cavity wall and every compartment floor or other wall or door assembly forming a fire-resisting barrier
• In roof spaces
• In external facades/cladding
• To protect escape routes

Fire stopping is used to provide continuity where gaps, imperfections, joints and small openings are present in fire-resisting elements of construction. Fire stop products are used to seal around small openings to close gaps and maintain the performance level of the wall or floor. As such, fire stopping will be expected to be of the same fire resistance as the element of structure to which it is fitted or attached.

Any fire-stopping test must be relevant for the construction method being used, and variations between the as-built construction and the tested assembly may invalidate the application of the test results.

The installation of these fire safety and protection measures will be undertaken as the building process proceeds. Whilst this is the case for all buildings regardless of material, relevant considerations for timber buildings specifically are the focus here. This important aspect of ensuring fire safety in timber structures has been, and remains, a focus of research. Further reading on this is available, for example:

• Fires in cavities in residential buildings (2013) The performance of cavities barriers in external walls with combustible materials, NHBC Foundation, 2013
• Design principles for fire safe detailing in timber structures (2020), Werther N. et al World Conference of Timber Engineering Santiago, Chile

Cavity barriers are typically of non-combustible material, fitted within cavities horizontally at each floor and vertically at each party wall and around all openings. The specification and selection of cavity barrier systems is key to achieving fire safety but is not always firmly and reliably owned by a specific supply chain partner in the construction process; architects can defer the specification to the contractor; often key decisions are further deferred to the passive fire protection installer. Whilst generic systems and products are available to guide decisions, specific manufacturer and system type should be specified for a project. The installation needs to be approved by a competent review and sign off. As cavity barriers are typically hidden by the progress of the construction process, it is critical that final as-built and maintenance information is collated (see Information management in timber buildings).

The following will influence the product choice:

• Expected building movement. This could be due to future settlement, shrinkage, differential thermal expansion, deflection or sway of structural elements.
• Expected collapse or deformation of structures or surfaces that the cavity barrier is attached to.
• Services such as ducts or pipes.

Approved proprietary systems are available from many suppliers.

Any product chosen should be third party certified or CE marked and tested using relevant standards. Third-party standards such as RedBookLive are also available and often requested by insurers. This can increase confidence that the product is fit for intended purpose and manufactured to constant quality. Evaluation will consider

• Factory production control
• Initial type testing
• Appraisal of the product test and assessment against a technical schedule and scope of application
• Traceability of product
• Traceability through labelling

For a selection of third-party certified products see RedBookLive.

Other schemes and certification providers are available, here only shown as an example, see UKAS for more information and a full list of UK providers.

The quality of installation of cavity barriers is vitally important to providing compliant and performing cavity barrier and fire stopping solutions. Local fire and rescue services carry out inspections to help ensure buildings are compliant. The Association for Specialist Fire Protection (ASFP) is a leading advocate for driving standards across the industry, bringing focus to installation standards and quality of workmanship. The ASFP currently recommends the use of installers part of UKAS accredited/approved schemes.

Specific considerations for timber construction
In addition to guidance in the Building regulations, other publications are available: for example for lower rise construction, The Structural Timber Association Fire Safety In use guidance Volume 2 – Cavity barriers and fire stopping 

As industry guidance evolves, every effort will be made to update the site to signpost additional information. Current information, linked above, covers functional requirements for cavity barriers in typical timber construction projects, roles and responsibilities and cavity barrier locations, detailing and ‘care points’ for the various supply chain interactions. It also highlights the use of competent and trained installers, as well as provision of photographic evidence of installed cavity barriers and firestops. This forms part of the STA Site Safe policy. For more information on quality assurance schemes available for timber construction, please see https://www.structuraltimber.co.uk/sta-assure/.

Modular construction
As construction techniques evolve and with increased use of timber solutions in modular construction techniques, attention to detail is key. Fire events have identified issues with the provision and quality of installation of fire protection products and systems in concealed spaces in this type of construction. These forms of construction introduce additional voids, cavities, and shafts into buildings and where modular construction is employed cavities between modules must be carefully considered, designed and managed.

For further information see Fire Safe Use of Wood in Buildings. Global Design Guide.

Facade cavities
Fire propagation through and over ventilated facade systems is a key to achieving fire safety for occupants in and around the building and for emergency services. In the external layer of the building, cavities are the norm, especially in the UK where facades are generally ventilated to ensure adequate moisture control and weather tightness. These cavities can present significant path of fire spread in the event of a fire, resulting in loss of life and property.

Several literature reviews and large-scale experimental studies have been completed and research continues (see Reaction to fire performance – external surfaces). Various test methods are used throughout the world to assess and evaluate the performance of facade solutions, including cavity protection systems. According to the testing experience at BRE, flames in ventilation cavities can extend up to ten times further than flames outside the cavity, as reported by Colwell et al. An air cavity also contributes to increased burning rates in the cladding system, see Boström et al.

Careful detailing and third-party assured cavity and fire stopping products manage these risks, if installed and executed correctly. This needs specialist review and supply chain engagement, as the chosen cavity barrier must retain its ability to control moisture as well as perform adequately in the case of a fire. An overview from Fire Safe Use of Wood in Buildings. Global Design Guide illustrates the basic principles of managing fire spread, whilst allowing for ventilation, see below. The use of self-expanding, or intumescing, cavity barriers is often considered, and products are available for timber construction. This requires careful review and detailing, confirmation of acceptable activation temperatures and overall alignment with the fire safety objectives for the project. Early and continued liaison with the design, construction and client team is recommended to ensure compliant and reliable management of risks.

Separating timber wall and floor assemblies covered the design of fire resisting timber construction, as has also been outlined earlier in this section. For this performance to be delivered it is assumed that:

• Joints between panels are tight or filled with fire resisting material,
• Linings are installed so joints are staggered and
• Fixings are inserted as per manufacturers’ instructions.

Joints between structural elements have also been covered, and standard set-up for wall-to-floor and floor-to-floor joints can be found for example in Table 9.1 Global guidelines for element joints in Fire Safe Use of Wood in Buildings. Global Design Guide.

Information on protecting the installation of building services and fire compartmentation, including  service penetrations, exhaust systems and ventilation ducts, is available in Fire Safe Use of Wood in Buildings. Global Design Guide as well as here https://asfp.org.uk/page/Publicationslist.

Information on fire doors can be found here.