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Structural timber is an innocent casualty of ungrounded fears over fire safety

Google’s king's cross hq by big and heatherwick studio. © heatherwick studio

Mass timber can help us tackle the climate emergency safely and we cannot afford to ignore it, says Maribel Mantecon

Following the Grenfell Tower fire tragedy in 2017 structural timber, along with all combustible materials, has been banned in the external walls of residential buildings above 18m. Public safety is paramount and there was clearly a need to provide reassurance. Yet structural timber has become an innocent casualty.

In the midst of a climate emergency, structural timber can play a key role in assisting with the removal of carbon dioxide from the atmosphere and give us a chance to avoid catastrophic and irreversible climate impacts.

We must radically cut carbon emissions and cannot afford knee-jerk reactions that may undermine our efforts to do all we can to secure a future for our children. What we need are carefully considered strategies and regulations.

Since the Great Fire of London in 1666, timber has been generally perceived in the UK as unsafe, especially compared to the two most common structural frame materials, concrete and steel. However, concrete and steel represent a staggering 11 per cent of global carbon emissions and we really need to look elsewhere moving forward. To put it into context, concrete’s carbon emissions are 550 kgCO2/m³, steel’s 12,000 kgCO2/m³ while, in comparison, cross-laminated timber has a negative emission of -600 kgCO2/m³.

Clearly not all timber products have the same level of fire-resistance. Mass or engineered timber can match or exceed the performance of concrete and steel. In the UK, structural elements over 18m require two hours of fire protection. Under test conditions, 180mm cross-laminated timber lasts over three hours. Performance-based fire engineering needs to be taken into consideration to meet building regulations.

Prefabricated engineered timber and modular CLT also have the sustainable benefits of reduced waste and energy during manufacturing.

Laminated glass balustrades, also included in the combustible ban, are being considered for exception. Yet, although the RIBA had called for structural timber to be exempt, this has not been taken up by the government. How can it be that there is the time and appetite to reconsider glass balconies, but not to review structural timber, which could make a significant shift towards zero-carbon buildings?

Of course, making buildings safe is a given, but there is a misunderstanding here that needs to be put right. And it needs to be done quickly.

By using off-site manufactured structural timber with non-combustible insulation and cladding, we can design buildings that are safe, better for the environment and for our wellbeing.

In Copenhagen, a beautiful all-timber district is being planned. In the USA, where it meets building regulations for fire safety via testing, mass timber is being embraced with large glulam columns and beams often appearing instead of concrete and steel in large buildings.

The world’s tallest timber building, the 18-storey Mjøstårnet Tower in Norway, has been designed to withstand a fire that is left to develop freely without active extinguishing and now Sweden has unveiled its own tall timber building, the Kajstaden scheme by CF Møller Architects.

If these countries can put safety procedures in place to allow them to build with timber so can we. We must insist that the government reviews this, puts in place fire test compliance that permits the use of structural timber members and encourages further research and development in this field. Without this, not only will we fall behind other countries but we risk missing our legally-binding 2050 Net Zero target.

Current regulations here result in strange contradictions. Google’s new headquarters in King’s Cross by BIG and Heatherwick Studio will boast the largest wooden façade in the world (pictured) and this is considered acceptable as it is an office building. But in the residential sector, all over the country even small four-storey housing developments are seeing modular CLT being designed out.

Mass timber can help us tackle the climate emergency safely and we cannot afford to ignore it.

Maribel Mantecon is an associate at CZWG Architects


Readers' comments (7)

  • Populist politics has surely crept into the factors influencing government attitudes in Britain - looking at the images of CF Moller's Kajstaden tower the timber clad balconies are surely something that in the UK would now be out of favour following a few alarming fires caused by barbecues.
    I once tried to persuade a boatyard owner that a large span portal framed shed would be more secure against collapse in a fire if it were a timber rather than steel structure, but he was having none of it - and unfortunately public opinion (at present, anyway) is likely to be more heavily influenced by the horrors of the likes of the fires at Lakanal House and Grenfell Tower than by the unfolding horrors of the sheer human ineptitude that enabled these disasters.

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  • I'm no fan of CLT (Dartington Primary School) but there is little doubt that, it , and heavy timbers, perform well in a fire.
    Again - sorry to bang on about it - ditch The Building Regulations - Go IBC.

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  • I thought that Dartington Primary was the victim of criminally deficient specification of the external skin, but if non-disclosure agreements were part of the liability settlement we might never get to know.
    This in itself could surely be termed criminal - and unless the construction detailing strayed from what received local authority building approval it should be a matter of public record.

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  • Robert,
    Had the same thing happened in the USA then indeed it would have been criminal; and had a decent lawyer been on the case it would have been deemed so here.
    I had quite an education in the apathy of bureaucracy during a fairly extensive correspondence with Devon County Council which finally ended when the DCC, Jan Shadbolt, informed me, after I had suggested incompetence was evident on all sides, that she would no longer respond to my concerns.
    There are several millions the taxpayers of Devon are still out of pocket.
    It was only after FOI requests was I able to learn of the settlement amount.
    I've been in the construction industry as a designer and contractor for most of my life and can confidently state the fiasco was way beyond anything I could have imagined.
    As to your point Re: the failing fabric. It is surely definitive proof of the unsuitability of CLT if a structure built of it has to be demolished in the event of moisture intrusion.

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  • Some bold figures quoted there. Could you provide a source of the -600kg CO2/m³ for CLT?

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  • Hi Colin, yes, these figures should really make us sit up and pay attention-my source for them was FCS's Carbon Counts research and current exhibition

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  • No mention of the tallest timber building going up in Milwaukee Wisconsin. It is my home town so I am a bit biased. It is going to be 23 stories and all residential. https://archinect.com/news/article/150161330/milwaukee-s-wooden-skyscraper-just-got-a-little-bit-taller

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