An insight into timber in construction and regulation following the Barking blaze

Materials World magazine
,
1 Jul 2019

A fire that engulfed a block of flats in London has brought timber under scrutiny. Shardell Joseph looks into timber in construction, regulations and the impact of misconceptions. 

A fire broke out on the Samuel Garside House development in East London, UK, on 9 June 2019. The blaze destroyed a block of 20 flats in minutes, with 10 damaged by heat and smoke. While cause of the fire is still under investigation, it was reported that a resident on a lower floor balcony was seen lighting a barbeque shortly before it began, but a direct link is as yet unconfirmed.

Timber has since taken the hot seat in a wave of scrutiny, with a particular focus on the use of timber cladding. A fire risk assessment carried out by Osterna identified the decorative wooden cladding used on the balconies as a significant hazard. Due to this, the incident has been compared with the Grenfell Tower blaze, which killed 72 people on 14 June 2017, and its use of highly flammable cladding.

However, the Timber Trade Federation (TTF) and the Wood Protection Association (WPA) claimed in press statements that timber cladding was not the issue here, but rather that the lack of a flame retardant treatment created an unnecessary fire risk, even though it was not required by building regulations and those used were approved by Building Control.

‘If a comprehensive fire risk assessment had been conducted on this design it would have been clear that additional protection was required in these particular circumstances,’ said TTF Managing Director, Dave Hopkins.

Timber coming under fire

Timber has significant advantages over masonry in construction, mostly for the speed and cost of construction. Along with this, timber offers reductions in labour and occupational risk, and a greater degree of architectural quality with the majority of the structure being built under factory conditions.

Wood burns well, and when timber’s infamous fire burning properties are considered in the context of incidents such as the Barking block fire, it is easy for misconceptions to spread. However, in a UK government report, Analysis of fires in building of timber framed construction, England, 2009-10 to 2011-12, no evidence was found of the difference in the distribution size of fires between timber-framed buildings and those without special construction, such as steel and concrete.

‘Timber is a safe material for cladding where suitable measures are taken to minimise risk. For example, avoiding locations close to waste stores or structures where ignition could occur,’ Wood Technology Society Vice Chair and IOM3 Fellow, Morwenna Spear, told Materials World.

‘This element is partially covered by the building regulations relating to the approved boundaries, mentioned above, and partially relates to best practice, and good design by practitioners.’

Treating timber

There is a vast difference in fire resistance when timber has been treated with a fire retardant. After the Barking fire, leading timber trade associations including TTF, WPA, and Timber & Decking Cladding Association raised the issue that the timber components used in these balconies would have performed very differently and would not have been engulfed in flames so quickly if the wood had been treated with an industrial flame retardant prior to installation.

Untreated wood typically has a Euroclass rating of D - combustible material with medium contribution to fire - or E - combustible material with high contribution to fire. But when treated under factory conditions, this rating can reach as high as B - combustible material with very limited contribution to fire.

‘While it is not possible to bring any organic substrate, including wood-based materials, to a Class A rating, flame retardant enhanced wood-based materials improve safety, add value and are fit for purpose for many applications,’ Wood Protection Association Executive Chairman, Stephen Young, told Materials World.

Jerry Quayle & Associates Managing Director Passive Fire Consultant, Jerry Quayle, added, ‘We can get a Class B out of a piece of timber with a sufficient treatment, the chemicals on it, or with a coating.

‘So you could coat it and get the Class B, meaning it doesn’t burn very far when there’s a source of heat underneath it. When you take that source of heat away, the fire goes out.’

The timber used on the balconies of the flats has since been identified as ThermoWood, also known as heat treated timber – unrelated to fire retardant treatment – which has a Class D fire rating if untreated. It was revealed in a post-incident assessment, carried out by Osterna, that the external cladding, wooden joists and deck balconies were a significant hazard, putting residents at risk of smoke inhalation and burn injuries.

Regulating timber structures

Reflecting on the regulations imposed on timber construction, Young posed the question, ‘If the construction burned as quickly as reported, should standards change?

‘We believe that a fire risk assessment would have highlighted the potential risk of using Euroclass D rated material i.e. untreated wood, and that enhanced reaction to fire properties such as Euroclass B or C would have mitigated the ignition, spread and damage caused by the Barking flats fire,’ Young said.

Since Grenfell, there has been a call to tighten building regulations. In 2018, following Dame Judith Hackitt’s Independent review of building regulations and fire safety report, the government amended the regulations, promising to ban combustible cladding by prohibiting the use of combustible materials anywhere in the external walls of high-rise architecture. The higher Class B is required for external surfaces on buildings above 18m, but there has been no standard set for buildings below this height.

Anything below 18m can have cladding fire rating as low as Class D, which is evidently a significant fire risk. The ThermoWood used for the construction of the Samuel Garside House was Euroclass D with S2 rating, indicating a high amount of smoke emitted during burn. As such, the building had very little protection and was engulfed in less than six minutes. At present, there are no regulations that make it compulsory to treat wood with fire retardants before construction.

Major government-backed changes to fire regulations are now expected. It comes as no shock, however, to know that people within the wood industry are still calling for even tighter regulations on smaller buildings and the implementation of fire retardant treatments.

‘Better and clearer systems are required across the board to ensure that designs on paper are fully checked, and that built structures are found to fully deliver the specification and standards,’ Wood Technology Society Board Member and IOM3 Fellow, Jim Coulson,
told Materials World.

According to Wood Technology Society, ‘The key issue is that building regulations throughout the UK are – despite the recent changes in the English fire regulations – less restrictive towards timber clad façades and balconies than most other countries.

‘The façade design at Barking would not have been permitted in Scandinavia, most of continental Europe or North America.’

The future of timber in construction

In the wake of the fire, there has been a huge amount of attention on timber and its use within the construction industry. The Sunday Times conducted an investigation into timber cladding in the UK, which reported that 12,600 flats with timber cladding are being investigated for safety. Also, housing associations such as Clarion, L&Q and Peabody have claimed to be carrying out work to deal with potential issues arising from ThermoWood.

Regardless of the impact treating wood could have on fire safety classifications, some speculate the likely knock-on effect these fires,
and subsequent material misconceptions can have on the use of timber in construction.

‘There is potential for negative feedback on greenhouse gas reduction within the construction sector if poor design and instances such as this fire lead to a move away from sustainable and renewable materials in construction,’ said Coulson. ‘However, safety of structures must be ensured, regardless of construction materials and systems used. This is most appropriately considered within the building standards.’

Timber has become an increasingly attractive material in construction due to being a carbon-negative material, as it is believed to play a positive role in reducing global emissions globally. It is now up to all players in the chain and regulatory bodies to ensure all timber constructions are properly treated and built to a high safety standard. Only then, with education to combat misconceptions, can the timber and construction industry rebuild public trust in the material.

‘The case for using more wood in construction to support the carbon reduction policy of the UK is now well recognised but the use of wood must go hand in glove with initiatives to improve understanding of correctly specifying timber materials and installing them correctly,’ said Young. ‘Timber industry trade bodies like TTF and WPA have agreed to work together to help tackle this.’