Summary
• IWS led an intensive R&D project to develop a robust fire retardant system for timber frame construction.
• Arch Timber Protection was one of the development partners.
• The FR system reduces ignitability, fire propagation and spread of flame.
• Tests have demonstrated a reduced radiant heat and prolonged burn time.

The timber frame supply chain has the credentials, through its speed of construction and carbon-neutrality, to assist the construction industry to deliver its objectives in respect of the volume of housing and the low carbon agenda. But, as with all methods of construction, timber frame has its challenges, principally fire during construction.

Correctly built, completed timber frame buildings are no more vulnerable to fire than any other method of construction. However, during construction the timber frame elements can be left for a period without finished fire protection applied and this phase of the build process is less robust against arson attack.

The key issues are:
• rapid fire growth;
• intensity of the heat generated;
• risk of collateral damage to neighbouring buildings;
• insufficient window of opportunity for fire fighters to extinguish flames.

A project led by Intelligent Wood Systems Ltd (IWS) embarked on a programme designed to reduce the risks involved with fire for timber frame during construction. The project, which has involved more than 12 months of intensive research, has been a collaboration to develop a fire protection system specific for timber frame. The system was launched at Ecobuild in March.

The project team identified early on that flame retardants (FR) should form a key element of the protection, in conjunction with a strategy that focuses on limiting the growth of fire, as this will subsequently reduce the peak heat output as a by-product.

The team was aware that certain FRs for timber are brominated or highly acidic and that the toxic nature of certain product types has had an impact on perceptions and raised concerns about their safety. Therefore, it was important to use specific chemistries that are free of all metals and halogenated compounds, including brominates, and have more favourable environmental credentials as a consequence.

The water-based double-vacuum treatment fire retardants used were developed with partner Arch Timber Protection to provide fire protection for the lifetime of the building – and, crucially, through the construction stage. A purple dye added during treatment provides a way of identifying that the timber components are IWS-FR treated.

Improved performance

Suitable FRs should considerably improve the performance of timbers and sheathing materials against fire and are critical to the robustness of the solution from all angles. They will provide protection internally to the timber frame walls and externally in the cavity through the treated sheathing. If an arsonist compromises the additional layers of protection on the panel, the treated structural timbers will still provide a significant layer of protection.

The resulting solutions will minimise concerns regarding timber frame during construction as the FR system can reduce ignitability, fire propagation and spread of flame. Small-scale test results have shown a reduction of generated heat and larger-scale tests have demonstrated a 70-times reduced radiant heat and prolonged burn time, presenting opportunities for fire crews to tackle situations before they become unmanageable. Tests also showed the capacity of a fire to self-extinguish.

Surrounding buildings

The potential for flammable structures to form a bridge between occupied buildings outside the boundary of the new build and timber frame under construction is a recognised risk by the Health & Safety Executive (HSE). It goes so far as to say in its Fire safety in construction publication:“In situations where fire spread from a construction site might endanger the lives of people in adjacent properties, and effective precautions to reduce this risk to an acceptable level cannot be identified or implemented, alternative build methods with a lower fire risk must be adopted.”

HSE is clear in its guidance that it is the potential radiant heat from a timber frame building on fire during the construction period that must be controlled. The IWS-FR System built into the entire timber frame structure provides a greater resistance to growth of fire and delivers robust protection as proven by tests to reduce fire risks.

FR systems used in conjunction with the UK Timber Frame Association’s 16-step risk assessment approach reduce the growth of fire, which in turn reduces the radiant heat and ultimately lowers the risk for timber frame.