FEATURE FIRE PROTECTION
Safety at All Costs Robin Lancashire, senior timber frame consultant at BM TRADA, explains key considerations to bear in mind when designing and installing timber frame cavity barriers.
W
ith timber frame construction expected to continue
installation that must be considered to ensure both buildings and the
growing in popularity, it’s critical that any building
people within them are protected.
made from the material is adequately protected
Cavity barriers prevent smoke and fire tearing through
against the spread of fire.
There’s no denying that timber is growing in popularity as a
Recent fire events in various building types have highlighted the
building material. According to a study by MTW Research, timber frame
performance of cavity barriers and how they are installed in buildings.
housebuilding was expected to see a £70 million increase in 2022, with
Cavities act much like a chimney, so without a properly designed barrier,
demand rising rapidly across both residential and commercial building
fire and smoke can quickly travel unseen through what can be an
sectors.
extensive network of connected spaces in a building.
It’s not hard to see why either. Timber is a highly sustainable
National building regulations stipulate where cavity barriers should
material and can capture carbon better, unlike other materials such
be installed, what they should be constructed of and how they should
as steel and aluminium. Alongside this, it’s fast to build with, so the
be fitted. There are some regulatory differences between the nations
commercial benefits are significant for developers.
that make up the UK, both in terminology and specific requirements,
However, while the growth of timber construction is a good sign,
but the principles are all the same – limit the spread of fire in a cavity.
safety remains vital. This is where the importance of cavity barriers
Balancing ventilation and fire safety
comes in, and in the event of a fire, they must be able to perform as intended. There are some key factors around design, specification and
One of the first decisions to make is how to balance ventilation with fire safety. When building with timber frame, it is important to accommodate the requirement for cavity barriers while also ensuring timber elements remain dry and below the decay threshold (a moisture content of 20% of less). Timber frame construction needs a drained and vented external wall cavity behind all types of cladding. This provides a space where moisture vapour that travels through from the warm side of the wall to the cold side can ventilate away, without forming damaging interstitial condensation. The external wall cavity is also a line of defence from the outside. It prevents wind-driven rain or leaks through the cladding from directly wetting the timber frame structure by letting moisture drain away freely. The key challenge therefore is to provide cavity barriers where required, while allowing the timber frame structure to drain and vent. For those designing and building with timber, the Timber Frame Construction (5th edition) is the go-to publication to reference. The cladding chapter of the book provides detailed information on the
Timber Construction Magazine
Spring 2023
28
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