When fire struck at a timber frame construction site in Colindale, north London on July 12 last year, the sector collectively held its breath and waited for the fallout.
No company was more focused on any possible backlash than BSW Alouette. It had just completed phase one of a 1,000-unit Berkeley Homes development at Holborough in the south-east of England and was on the brink of securing phase two (TB Summer 2006).
But the company did more than sit back and wait: BSW Alouette, along with its timber engineering consultant FrameSolve Ltd, swung into action and enlisted the help of IFC Certification Ltd. The result was a fire risk mitigation scheme robust enough to persuade Berkeley to stick with timber.
Implementation of the scheme significantly reduces the risk of fire breaking out during construction and, should the unthinkable happen, reduces the risk of spread of flame.
The senior managers of IFC Certification are all timber technologists, an important credential, as director Jerry Quayle pointed out. “There are no unforeseen dangers about using timber frame in large developments and timber is no more dangerous than any other material on a construction site. However, one must always treat timber with respect and be aware of its properties, particularly where fire is involved.
Temporary fire doors close off individual compartments: each door is numbered and is reassessed before reuse elsewhere on the site
“In an industry where concrete, bricks and mortar have dominated for the last 150 years, perhaps some of this inherent awareness and respect has been lost,” he said. “Bad practices and carelessness have crept into the construction process, which leaves large developments of a size previously unseen in timber fame in the UK very vulnerable to accidental ignition.”
Sharpening up site practice, which in many respects is down to good housekeeping, is at the root of the fire risk mitigation scheme. The first step is an independent assessment of the site to identify any potentially hazardous areas or practices.
As very few construction site fires are caused accidentally, site security is crucial. As part of this, IFC Certification carries out a “socio-economic review”, looking at factors such as the local crime rate and press coverage of the project.
The layout of the site and the unit design is then scrutinised plot by plot, and risks associated with the different design types and their location are analysed before attributing them high, medium or low risk status. Footprint, height, configuration, the nature of external linings/claddings, insulation and internal linings and the separating capability of temporary and/or permanent compartmentation are all considered. Once those ratings are in place, a monitoring schedule can be drawn up and implemented.
Fire extinguishers are in ample supply, as are small skips for safe disposal of waste wood and manual fire bells should the alarm need to be raised
There is no hot work, such as welding, carried out until after the site is handed over to Berkeley, so the risk of sparks is negligible. However, where portable generators are used, spare fuel is stored away from the area and funnels are used for re-fuelling, avoiding the risk of spillage. Access to building materials and components is also strictly controlled; there is no storage of combustible material within the timber frame and no bulk storage adjacent to it. Only the material used on each specific part of the build is brought from central storage when needed.
Within the frame itself, the chimney effect present before the staircase is installed is tackled by installing temporary third party-certified fire doors between the compartments. Each door is numbered so that when it is used elsewhere in the build, it can be reassessed to ensure it is still competent for fire integrity. Other voids, such as windows, are similarly closed off.
The measures aren't all linked to neat and tidy site practices, however. BSW Alouette has also changed its manufacturing processes to accommodate fire mitigation measures. The closed panel walls now incorporate a fire separation wall. This is clad in Fiberock, a plasterboard made by US Gypsum, which has a one-hour fire resistance. The Fiberock is fixed in place with a special screw pattern – a greater number of screws ensures the Fiberock stays in place longer in the event of a fire and has the added benefit of improving racking.
The pre-lined party walls are installed at the same time as the exterior walls, even before the floors are put in, so from an early stage the build is compartmentalised. Once the floors are installed, a cavity barrier runs horizontally between levels to reduce the spread of fire and hot gases upwards.
The Holborough development features seven designs and includes 20% social housing
Site monitoring is carried out regularly, from daily to monthly, depending on the risk rating. IFC Certification started the surveillance and then trained BSW Alouette site managers and FrameSolve consultants who carry out interim inspections. These inspections, some unannounced, are videoed, then logged on paper and retained until the unit is handed over.
Significantly, the measures that have been implemented don't hinder the build process. “The aim is to make the site as low risk as possible for a construction site without stopping it working,” said Quayle. “It's thorough, but non-invasive. The builders are never waiting for us, we're always ahead of them.” And, he added, the scheme was an enhancement of the “very good fire protection system” already in place.
IFC Certification and BSW Alouette are convinced that the company's pragmatic response to the Colindale fire will stand it in good stead. “We'd like to roll out this to all our clients,” said Norman Gore, BSW Alouette managing director.
It's a marketing tool for IFC Certification, too: “We'll be putting it out into the market place,” said Jerry Quayle. Once it's tried and tested, the company can apply for UKAS accreditation of the scheme. This is just stage one. Stage two is on the drawing board and aims to design out the risk. It will provide innovative solutions outside the guidance of Approved Document B.”
In the shorter term, of course, implementing the scheme and altering its manufacturing processes secured the project for BSW Alouette. “We would have lost phase two if we hadn't put all this in place,” said Gore. “Compartmentation was the key that persuaded Berkeley to stick with timber frame.”
“And,” said Luke Whale, FrameSolve director, “they needed an independent expert like IFC Certification to attest to the fact that timber frame developments are as safe as any, including masonry.”
“It's our opinion the scheme will give the developers the confidence to remain with timber frame,” said Quayle. “There are few better construction systems than timber frame at meeting the needs of the builder and developer with regard to speed, efficient use of materials and environmental requirements and it must not be prevented from reaching its potential.”
