The rules

Fire expert warns of roof risks

Poorly positioned service ducts are creating a fire risk in roofs, a leading fire expert has warned.

Speaking last month at a seminar run by insulation manufacturer Rockwool, Martin Shipp, associate director of the fire investigation body Fire Risk Sciences, cited 10 potential fire risks in roofs.

Ductwork was highlighted because maintenance teams often find it impossible to check fire dampers when service ducts are installed in inaccessible spaces.

Fire dampers are valves in pipes that automatically close in the event of a fire to prevent flames and hot gases from moving between rooms and roof spaces.

The FRS has also found that absent or poorly fixed cavity barriers are increasing the risk of fire. The specification of inappropriate cavity ties, such as those made from nylon, was exacerbating the problem.

The eight other potential fire risks in the roof that Shipp cited were:

• Placing smoke control intakes too close to smoke outlets
• Failing to align duct dampers with the fire barrier that they penetrate
• Failing to fire-stop cable or pipe penetrations through compartment walls (even when the cable is the fire alarm system)
• Using polyurethane foam as fire stopping
• Removing passive fire protection from structural steel (in one example, it was in the way of a ventilation duct)
• Increasing the number of cables squeezed into cable ducts
• Always testing the same zone of a smoke control system
• Installing smoke control curtains incorrectly, including in roof spaces, so that they fail to touch the floor.

The findings of FRS, which is the fire division of BRE, are likely to appear in future Building Regulations. Part B, covering the prevention of fire, is being reviewed and a consultation paper will appear in spring 2005 before an updated document is introduced in 2006. Consultations with bodies such as the FRS give the Office of the Deputy Prime Minister an early warning of topics that need to be addressed in the Building Regulations.

BRE is holding a fire conference on 30 September. Contact Sarah Hill 01923-664700 for details.

BBA approves ventilation-free roof spaces

The British Board of Agrément has published guidelines for roof systems without traditional eaves ventilation.

In a recent technical paper, the BBA said specifying this type of roof system is "sound and practical" as long as design and installation instructions are strictly observed.

The BBA said that vapour-permeable membranes could be used without ventilation in cold-pitched roofs, as long as measures are taken to limit the ingress of water vapour into the unventilated space.

The announcement follows a row between vapour-permeable membrane manufacturers Glidevale and Dupont Tyvek over whether the space between the membranes and the roof covering should be ventilated.

Glidevale had complained to the Advertising Standards Authority about a claim by Dupont that all its membranes were suitable for use in cold-pitched roofs without having to ventilate the batten space between the membrane and the tiles or slates.

Dupont had said its product met the requirements of British Standard BS5250:2002 Control of Condensation in Buildings and had BBA approval for all types of pitched roofs.

The ASA upheld the complaint as BS5250 recommends ventilating the batten space and because the BBA approval only covered dwellings.

Dupont Tyvek has now been granted a BBA certificate for a new version of its breather membrane. The product is called Universal Tyvek Supro and its certificate replaces the previous 9913635 certificate.

The BBA paper also recommended that all penetrations into the roof space should be properly sealed and that extractor fans should be used to remove vapour in rooms with high humidity.

It added that specifiers and designers should follow the design and installation instructions in the BBA certificates of roofing membrane manufacturers.

The BBA came to its conclusions after developing evaulation software in conjunction with membrane suppliers and manufacturers. The program models the dynamic movement of vapour in various roofing constructions and takes into account factors such as wind velocity, vapour permeability of the tile underlay and internal/external humidities and temperatures.

• Details of approved products can be found at www.bbacerts.co.uk. The technical paper on breathable membranes is available on the website.
• An updated version of BSS250 is expected in early 2005. A public consultation paper is due to be published this month.