Metal web joists and light weight engineered joists are becoming increasing popular in the construction industry, particularly for home builds.
This type of joist does offer many great benefits over traditional solid timber joists, however this type of ceiling construction is highly reliant upon maintaining the integrity of the plasterboard protection to prevent premature failure.
In wood-based floors failure will occur some time after the fire has entered the floor cavity and started charring the joists. In relation to solid timber joists, metal-web joists have less sacrificial material resulting in a reduced time to failure from when the fire entered the floor cavity. However with correctly tested fire protection products, metal-web joist floors can perform equally or better than solid timber joisted floors.
The major cause of the breaching of the plasterboard protection layer is the penetration of ceiling with recessed lights, ventilation air valves and ceiling fans. Until now manufacturers of “fire rated products” have generally tested only with solid timber joists as light weight joists are seen as being too onerous and require a much higher level of fire protection and simply better products.
Building regulations require that products are tested with constructions that are representative of those used in application.
Tenmat have now tested a range of downlight covers, fire rated ceiling valves and ceiling fans in the most onerous 30 minute full scale loaded BS EN 1365-2 with metal web joist floor ceiling construction, which produced a result exceeding the 30 minute performance by a full 10 minutes and so can offer products which not only fully meet building regulations but will also allow the extended safe usage of light weight joists systems.
Metal web joist fire test ceiling with 7 large penetrations protected by Tenmat products.