The update to Product Paper 4 in the STA’s Design Guide to Separating Distances During Construction further underlines the industry’s comprehensive approach to answering questions posed following a number of high profile timber frame construction site fires in recent years.
It follows successful testing by the timber frame and engineered flooring supply chain.
Open-web joists, comprising timber chords and nail plates, can now earn two points in the Product Paper – essential for achieving the highest level of timber frame fire mitigation – Category C construction. I-joists also have a new solution to meet the same level, potentially increasing their use in large developments within densely populated urban areas.
A greater range of wall assemblies have also been tested, including several systems, such as the Norbord Wall System, featuring inner sheathing of 3mm resistant board, outer sheathing face of 9mm Norbord No Burn OSB, fire retardant treated studs and 40mm Rockwool ProRox SL 930 insulation. The system combined with a decking solution using similar materials and I-joists protected by Rockwool, can achieve Category C.
Additional floor and wall combinations are also listed, including OSB manufacturer SmartPly’s system to achieve a B3 category construction, featuring fire retardant treated studs, SmartPly FR OSB3 11mm sheathing and stone wall insulation, while floors feature SmartPly FR OSB3 15mm decking and fire-treated solid joists.
Makers of non-combustible board – such as magnesium oxide panels – have also seen slimmer panels successfully tested and listed, including several at either 6mm or 6.5mm. And a new matrix table will allow an easy way of selecting products and systems to meet the necessary category of timber frame construction needed for projects.
“There is a significant increase in the number of options,” said Martin Milner, STA technical adviser, “and the timber frame sector is leading by example.”
“The first version [of the guidance] has been used widely and I hope the second will be also. Where the documents have been used, the construction projects have gone well without a problem with the Health & Safety Executive.
“Compliance with this document allows companies and developers to proceed with their developments without hindrance.”
MiTek, which produces the Posi-Joist open web joist, said it was delighted that its Posi-Joist Fire-Safe Plus product had been listed and could help meet the highest fire mitigation timber frame build category.
“For the majority of 2013 the Structural Timber Association’s guidance did not have a metal web joist or an I-joist solution for Category C build,” said James Morgan, business development director at MiTek Industries Ltd.
The Fire-Safe Plus metal web features fire-retardant treated 47mm thick TR26 chords and improved fixing of metal webs with additional Young Black nails which penetrate the core of the timber beyond a charring zone.
Another new listed open web solution capable of contributing to a Category C solution, a generic one involving a range of manufacturers, uses fire-retardant treated finger-jointed timber, with the top flange turned through 90 degrees and is particularly suited for deep floor applications.
