In my last post I presented an overview of the regulations relating to building in bush fire prone areas, with references to several relevant documents. It’s a little difficult to draw from that a simple list of building requirements, because specifications are somewhat dependent on the threat level assessed at a given location. For those wishing to simply improve existing structures, which are not subject to current regulations, there are nonetheless some guidelines that can be followed.
In general, the objective is to minimise the opportunity for embers to come into contact with fuel (flammable material) and to provide appropriate protection of more flammable building elements from radiant heat.
In this context, fuel, in the first instance, is most often leaf litter and other debris, rather than the building itself. The aim here is to prevent the build up of combustible material either by regular cleaning or by covering collection points, like roof gutters, with appropriate litter guards.
With regard to the building structure itself, the regulations for new work effectively require that there be no opening of more than 3mm in the structure (excluding subfloor). Any opening that is greater than 3mm should be either sealed by an approved method or covered with a mesh, made from corrosion resistant steel, bronze or aluminium, that has openings no greater than 2mm.
Sarking, behind weatherboards or external cladding and under roof tiles or sheeting, should be continuous and have a flammability index no greater than five (5). The installation of weather strips or draught excluders at the base of side-hung doors can also help.
Like many houses in our rural residential areas, my own (1980s) house is cedar clad with a corrugated iron roof. This cladding would be entirely unacceptable today, but if recladding your house with a more fire resistant material is impractical, simply painting the cladding to ‘bind in’ the nice little wood filaments that characterise a natural, rough sawn timber surface, can help to reduce the risk of attack.
With regard to the roofing, I was quite surprised recently when I removed a section of roof in the course of my current round of renovations. The roof itself is fully sarked, in line with current requirements, but the gaps between the ridge capping and the corrugated roofing material had allowed a quite considerable build up of fine leaf material and what was probably wattle pollen along the ridge line. Small birds or other wildlife had also managed to make their way under the ridge capping and make holes in the sarking with the result that there was quite a deposit of this fine, combustible material in the actual roof cavity.
There are various products available to close off these sorts of gaps in corrugated roofing, from foam infill strips to profiled metal flashings. These can often be retrospectively fitted, but some care is generally recommended in relation to ensuring that the material used is appropriately fire resistant.
Current requirements also restrict the materials that can be used in window frame and door construction, depending on the assessed Bushfire Attack Level (BAL). Glazing (the outer element in the case of double glazing) must generally be toughened glass and at least 5mm thick. Once again, replacing existing elements is often not practical, but when opportunities present themselves, it’s good to keep the relevant recommendations in mind.
These are just some of the more obvious building requirements. It should also be noted that building construction is only one element of protecting your property from bush fire attack. As noted in my previous post, the best place to start for anyone interested in further reading is the NSW Rural Fire Service (RFS) document Planning for Bush Fire Protection (PBP). If you are building or renovating, then the National Construction Code/Building Code of Australia (NCC/BCA) is the ultimate reference.