微密圈

Last week鈥檚 blaze at a Berkeley Homes development in Worcester Park, south-west London, is the latest in a spate of devastating fires. Residents testified to being woken by neighbours banging on windows and doors, telling them to get out of the four-storey building as the fire spread rapidly and firefighters struggled to get the blaze under control. In recent months, a series of buildings including a timber-frame care home in Crewe, a Holiday Inn in Walsall last month, and a Premier Inn vin Bristol in July, have burned down. These followed the flat fire in June that destroyed a new-build block on a Bellway development in Barking Riverside, east London, which had timber cladding.

All of these are on relatively low-rise buildings, and so far 鈥� thankfully 鈥� no-one has died or been seriously injured. But for those who have long been worried about the proliferation of timber-frame construction, a fatal fire is only a matter of time. 

鈥淚t appears the level of perfection required in construction only exists in the drawings 鈥� it鈥檚 very susceptible鈥�

Jim Glockling, FPA

鈥淲e鈥檝e had some very close shaves,鈥� says building surveyor Arnold Tarling, who has 30 years鈥� experience in fire safety. 鈥淚f we鈥檇 had a couple of deep sleepers, or disabled people, or people on medication 鈥� we would have had deaths.鈥�

Unsurprisingly, this spate of major fires is prompting some to question whether the government鈥檚 plans to tighten regulation in the wake of the Grenfell tragedy are far-reaching enough. The Worcester Park fire happened in the same week the government proposed reducing the building height above which sprinkler systems are mandated down from 30m to 18m 鈥� a regulatory change which would nevertheless leave buildings such as the 15m Worcester Park block unprotected. 

Meanwhile, some are calling for tougher action against timber construction specifically, while others even suggest the whole purpose of 微密圈 Regulations 鈥� which aim to protect people but not buildings themselves 鈥� needs to be looked at.

The case for timber frame

Timber-frame construction has grown more popular in recent years in the UK 鈥� it is lauded as a modern method of construction that is price-competitive and environmentally sustainable. Limited in its non-engineered form predominantly to low-rise construction, timber is lighter and naturally insulating, giving it a far lower carbon emissions impact than concrete, masonry or steel. According to a report on the market MTW Research, 58,000 timber-frame homes were started in 2018, with use of the technology expected to rise by 25% in the next four years. 

Andrew Carpenter, chief executive at the Structural Timber Association, says: 鈥淭imber is an outstanding renewable material that offers a range of environmental benefits. Add to this energy efficiency, speed of construction and offsite manufacturing methods [鈥�] it is important to continue to maximise the benefits of structural timber systems.鈥�

Andrew Mellor, partner at architect PRP, says: 鈥淲e鈥檝e got to look at the sustainability impact of our buildings, and the timber-frame argument around this really does have to be considered.鈥�

鈥淲hat if regulations change subsequent to you building something, meaning you end up with a building you can鈥檛 sell?鈥�

Andrew Mellor, PRP

Furthermore, many argue timber-frame buildings can be just as safe from fire as traditional masonry construction when guidelines are followed. Under 微密圈 Regulations guidance for low-rise buildings, this primarily comes down to the requirement to encase timber frames within a double layer of non-combustible plasterboard to provide an hour鈥檚 protection against fire spreading. Fire engineer Steve Cooper, director at consultant Tenos, says: 鈥淢y professional view is that timber is no more risky than any other form of construction, provided it鈥檚 built correctly and the detailing is done right.鈥�

STA鈥檚 Carpenter also argues that timber-frame buildings that have a robust build process meet safety standards: 鈥淐onstruction in accordance with regulation and manufacturers guidelines achieves building safety. We are working with designers, developers and regulators to ensure timber-frame construction continues to achieve higher levels of fire safety, which improves competency and compliance.鈥�

Warranty providers such as NHBC is also supportive of timber, saying: 鈥淲e consider timber frame as a suitable building material and we will continue to accept construction types that achieve compliance with regulations and standards.鈥�

For critics of timber frame, however, this requirement to build exactly to the drawing is the nub of the problem. Because timber is a combustible material 鈥� unlike concrete, masonry or steel 鈥� any breach in the materials protecting it can potentially make it vulnerable, something which could easily occur from DIY efforts by residents. Extra attention must also be paid to other elements of fire protection, such as fire stops in the cavities between the structure and the external cladding, to ensure these cannot conduct fire. Even Tenos鈥� Cooper, who maintains 鈥渨e can鈥檛 discontinue using timber鈥�, admits it is 鈥渓ess forgiving鈥�. 鈥淭here does have to be a recognition the detailing has to be better,鈥� he says.

Reality of building sites

微密圈 has uncovered some details regarding the construction of Richmond House, the block that burned down in last week鈥檚 fire (right), but what little has been confirmed appears to illustrate just how unforgiving the material is.

A spokesperson for the Worcester Park developer, St James, part of Berkeley Group, confirmed the block in the Hamptons development at Worcester Park was built with from timber frame, but said it clad with 鈥渇ibre-reinforced Portland cement cladding planking of limited combustibility鈥�. 

Tarling, who visited the site two days after the blaze last week, verified this description, and added that the timber-frame walls were internally lined, as required, with plasterboard, and moreover, filled with mineral wool insulation, which is also not flammable. 

Despite this, one resident, Stephen Nobrega, this week told The Guardian that within 20 minutes of him becoming aware of the fire it started 鈥渞ipping through鈥� the building from apartment to apartment 鈥� despite building regulations supposedly ensuring fires are held within each flat for a minimum of an hour before spreading. 

The London Fire Brigade said the blaze was already 鈥渋ntense and well-developed鈥� when they reached the scene, and that ultimately it took 20 fire engines and 125 firefighters five hours to get the 鈥渃hallenging鈥� blaze under control. 

For critics, of course, the fact the timber appears to have been surrounded by non-combustible materials, yet the fire still spread rapidly, underlines their contention that the theoretical safety case for timber does not allow enough leeway for the reality of building sites and human error. 

Jim Glockling, technical director of the Fire Protection Association (FPA), says: 鈥淎lmost every investigation ever made of real buildings says the fire-stopping is inadequate. 

鈥淚t appears the level of perfection required in construction only exists in the drawings  it鈥檚 very susceptible.鈥�

Extremely concerned

Surveyor Tarling points to the 1999 BRE fire test, which presaged the widespread use of timber-frame construction as a case in point. Initially reported by the BRE as a successful test result, 微密圈 uncovered in 2002 that hours after the fire in the six-storey construction was put out, the fire reignited, from burning embers not fully extinguished sitting within the cavity. 

鈥淚鈥檓 extremely concerned about the use of timber-frame buildings,鈥� Tarling says.

Campaigners claim the use of flammable structure means that when fires do happen, they result in much more destruction as they often cannot be contained. The fact the structure itself burns means fire crews often cannot enter buildings to fight the fires because of the risk of collapse. The FPA鈥檚 Glockling claims that while incidence of fire is reducing, the more widespread use of timber frame means that when they do happen, the destruction is far greater. 鈥淭his [Worcester Park] is probably the new normal,鈥� he says, referring to the fact the fire spread quickly, burning most of the block to the ground. 鈥淭here鈥檚 very little fire services can do to chase fire around a void when the structure is burning. This is going to be an ever-increasing outcome.鈥�

So far, published government data on residential fires does not seem to support this theory. Official figures report that the average area of damage from so-called 鈥渄welling fires鈥� fell by around one-third in the 2000s, and has largely plateaued since. Nevertheless, this rash of recent fires is prompting concern about whether the purpose of building regulations, currently designed to save lives but not buildings, needs to be looked at. Because in one sense, as Cooper says, the Worcester Park block 鈥渇unctioned as intended鈥� 鈥� in that everyone was able to escape the building before it burned down. 

The FPA鈥檚 Glockling says: 鈥淲e have to consider if this is what people expect the regulations to be doing. The regs are essentially about evacuation before collapse 鈥� not stopping a fire but slowing it down. But historically the government has only responded when people have died.鈥�

Attitude of insurers and lenders

Of course, even if the government is not focused on damage to property, there is some evidence the issue is catching the attention of lenders and insurers, who are particularly alert to fire risk in the wake of the Grenfell Tower blaze. PRP鈥檚 Mellor says he is aware that housing associations are getting 鈥渦nprecedented鈥� numbers of enquiries from leasehold tenants struggling to get a mortgage, because lenders are demanding additional information about fire safety. 

He says: 鈥淚nsurers and mortgage lenders are going to be focused on property. Mortgage providers have been asking for more reassurance around cladding, and I鈥檓 sure they鈥檙e now going to be looking more closely at timber frame.

Insurers are going to be thinking: 鈥榮hould we put premiums up? Or should we ask for sprinklers on these buildings?鈥� For the industry, there is now a question of whether sprinklers should be a requirement for timber frame at any height.鈥�

Laura Hughes, general insurance manager at the Association of British Insurers, said that since Grenfell, 鈥渋nsurers have tended to ask more questions to property owners on fire safety and management of a building鈥�, taking into account both 鈥渢he type of construction and any active fire safety measures in place such as sprinklers鈥�.

Mellor says concerns about resident safety, insurability and mortgageability have already driven some social landlords to install sprinklers on all blocks of four storeys and above, while both the RIBA and the RICS are backing calls for the government to go further than requiring sprinklers above 18m (around six storeys). 

A spokesperson for the RICS said it was urging government to require sprinklers on all buildings above 11m, as well as on others even lower 鈥渙n a case-by-case basis of risk鈥�, to 鈥渆nsure fires like the Grenfell tragedy and Worcester Park never happen again.鈥�

Former RIBA president Jane Duncan, now chair of the RIBA expert advisory group on fire safety, said the body backed installation of sprinklers in all new and converted residential buildings, and that while the cause of the fire at Richmond House in Worcester Park was not yet clear, 鈥渢he use of sprinklers as an additional layer of fire protection for such buildings is vital.鈥�

However, Tenos鈥� Cooper cautions that while sprinklers may help prevent fire spread they should not be seen as a panacea: 鈥淪prinklers may be an effective measure in timber-framed buildings in the event of a fire starting within the building, but are likely to be completely ineffective if a fire originates outside the building and breaks into the external wall.鈥�

He suggests the problem could be tackled by ensuring workers installing timber-frame buildings demonstrate an additional level of competency, such as has been recently proposed for those working on high-rise buildings. The problem for the industry, however, is what to do right now, with ongoing changes to building regulations guidance and a whole new Approved Document B expected in the next 18 months. 

鈥淭he problem is the uncertainty,鈥� says PRP鈥檚 Mellor. 鈥淛ust trying to keep up with all the change is extremely difficult. What if regulations change subsequent to you building something, meaning you end up with a building you can鈥檛 sell?鈥� 

It may be that, whatever the government ends up imposing, these commercial concerns mean the industry itself starts to change how it builds.

• Read more: Construction鈥檚 response to Grenfell