Different timber construction applications demand different fire retardant approaches and the latter continue to develop as wood is put to ever wider use.

The Osmose stable includes vacuum pressure impregnated FirePRO for interior above ground applications, from joinery to cladding, sheathing and joists. The product is BS EN 13501-1:2002-compliant and claimed not to compromise timber’s “engineering qualities”, including hygroscopicity.

For interior and weather-protected solid timber and sheet materials, Arch supplies Dricon, a water-borne, humidity-resistant retardant, Euroclass tested to EN13501. It is claimed to cut smoke emission and slow flame spread and flashover.

Like Dricon, Arch’s exterior application retardant, polymer-based Non-Com, can be CE-marked. It is also billed as low corrosive, providing biological protection and having “proven stability” in fluctuating humidity.

Meanwhile, Wolman Wood Protection is preparing for the full UK launch of its high-pressure impregnation Wolmanit Firestop. The product is already established across Europe and the company expects to have two Firestop treatment facilities in the UK later this year or early next.

“A key advantage is that it doesn't require major modification to conventional high-pressure treatment plants,” said Peter Fitzsimons of Wolman. “It’s also a straightforward process to operate, with no heating of treatment tanks or special curing considerations. That also results in clean-looking timber.”

Firestop, he added, is backed by a “full suite of performance data” and is under consideration for listing in the WPA's Fire Retardant Specification Manual.

Wolman also believes its presence in the UK will help generate fire retardant treatment demand generally. “One market barrier has been the difficulty of getting materials treated in a timely fashion due to limited treatment centre [numbers],” said Fitzsimons. “We hope to remove [that] by offering another option.”

Another product, HR Prof from Fire Retardant UK, has been developed for internal or external application and for the latter has been subjected by Sweden’s SP Technical Research Institute to NT 053 weathering tests.

Fire Retardant UK has also carried out “indicative tests” on HR Prof-treated OSB 3. “If further tests at a UK test house prove positive,” said managing director Chris Dilks, “formal SBi tests will be carried out to establish a classification.”

A headline issue for the timber construction sector recently has, of course, been fires in semi-completed timber frame buildings. As at least part of the solution, treatment companies are putting forward retardants for specific use when the frame is still exposed.

Osmose’s answer is its Protim Frameguard, a sister product to its I-guard preservative. The company stresses that construction site fire safety demands a “matrix management approach”, with site security to the fore. But, it maintains, Frameguard, which is tested to BS476 Part 7, adds a further safety element, as well as giving decay and insect protection.

“There’s little anyone can do to prevent a determined arsonist if they can access a building, but by giving protection against flame spread in framing timbers during construction, Frameguard can make starting fires more difficult and give extra time for people to respond,” said Neil Ryan at Osmose-using treatment specialist PTG Timber Treatments.

Dilks’s view is that ground floor panels in timber frame structures, where arsonists are most likely to strike, should be treated. “This may help prevent detractors of timber from pressing their case for brick and block,” he said. “It’s also likely to be more palatable to the timber frame industry on cost. However, not only should frames and studs be treated, so should the OSB sheets that give timber frame panels their structural integrity.”

Arch’s tailored timber-frame construction site product is Vacsol FR which also promises 60-year timber preservation.

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