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Engineered timber products such as cross laminated timber must be exempt from the UK government’s ban on combustible cladding materials, as they are essential in the global battle against climate change, say architects.

Waugh Thistleton – co-founders Andrew Waugh and Anthony Thistleton and dRMM founding director Alex de Rijke have all urged the Government to review its legislation, which prohibits the use of timber products on the external walls of residential buildings taller than 18 metres.

Waugh and Thistleton said the new policy “demonstrates a misunderstanding of the fire performance of engineered timber”.

“We are clear that mass timber construction is not a valid target for this change and will continue to advocate for its exemption,” said the pair.

CLT safer than steel in a fire

De Rijke, who has completed many buildings using cross-laminated timber (CLT), said the material is safer than steel in a fire.

“The government is mistaken to consider engineered structural timber materials, like CLT, as highly combustible thin cladding material,” said De Rijke.

“Mass timber is slow-burning, self-charring – even self-extinguishing, structurally predictable, and does not produce deadly toxic fumes in a fire,” he continued.

De Rijke gives Kingsdale School, the UK’s first CLT building as an example.

“dRMM were the UK’s first architects for a CLT public building in 2004 – the government-funded Kingsdale School – and accordingly had to present the European material to central government, local authority and fire brigade. All were convinced then and now by the evidence that, when properly sized and detailed, CLT is not only safe in a fire, but safer than many other standard industry materials such as steel – ironically the default material for buildings over 18 metres.

“Political knee-jerk reaction is uninformed”

The new legislation, titled Final Impact Assessment: Ban on combustible materials and external wall systems, states that only materials with a European fire rating of Class A1 or A2 may be used on the external walls of tall residential buildings, and states explicitly that wood products do not come under this classification.

This is “likely to slow down the use of engineered timber in future development in the medium to long term” it claims.

The policy was introduced in the wake of the Grenfell Tower tragedy, after it was confirmed that combustible cladding contributed to the fast spread of the fire.

Architects have largely welcomed the ruling, but insist that CLT should be exempt.

“This political knee-jerk reaction is uninformed and counter-productive. Banning safe timber construction prevents the creation of healthy and safe cities, and worsens the global environmental crisis of carbon emissions due to use of materials like concrete and steel,” said De Rijke.

“The Grenfell Tower fire was a tragedy and we fully support a ban on designing or building using combustible, volatile and toxic materials. But engineered mass timber is not one of them.”

UK is world leader in engineered timber construction

Engineered timber, also known as mass timber, is increasingly being championed in architecture as a sustainable alternative to steel and concrete structural frameworks.

Waugh and Thistleton claim that, even if the ban is maintained, the material is still crucial to the future of sustainable and fire-safe construction, as it is mainly a structural material not a surface material.

The pair have worked on numerous CLT projects, including the “world’s largest cross laminated timer building”.

“The new legislation does not propose a ban on engineered timber or CLT structures; it will simply change the way we build tall timber residential buildings,” they said.

“The UK is a world leader in the development of engineered timber construction with over 500 buildings completed. As the government acknowledges, this change in regulations will have an impact on the continued innovation and development of low carbon construction, and hence on the rate at which the construction industry can tackle climate change,” they said.

“It is imperative that architects recognise the impact of their work on the environment. Waugh Thistleton Architects will continue to research, design and build using low carbon technologies and reducing our reliance on concrete and steel.”

Source: Dezeen

The Government has confirmed it is banning the use of all combustible cladding on new residential buildings over 18m.

New building regulations will be introduced for external wall systems banning plastics, wood and other products that include combustible materials found in some aluminium composite panel systems.

Materials that would be allowed are those classed as A1 or A2 under the European Classification system.

Hotels and office building would be exempt because they have different evacuation strategies and the risks are lower.

Full details of the proposed ban have yet to be released. It is still not known whether the ban would apply to any material in wall construction from the internal face of the wall through to its external face, as first proposed.

If this proved the case internal wallpaper and paint, window frames, gaskets and seals, vapour membranes, surface finishes and laminated glass would likely be exempted.

To comply with the stricter requirements, it is estimated that for a 15-storey new build requiring 1,700m2 of cladding, a wall system which comprises only materials of A2 will cost an extra £25,000-£75,000.

Across England, this would equate to an expected overall annual cost of £7.5m-£11m assuming average build rates, according to the Government.

The Communities Secretary James Brokenshire confirmed the decision at the Conservative Party Conference.

“I can confirm that I will change the building regulations to ban the use of combustible materials for all new high rise residential buildings, hospitals, registered care homes and student accommodation.

“And bring about a change in culture on building safety.”

The new ban will be implemented through changes to building regulations to be brought forward in late autumn.

The plan to tighten up on materials use on building exteriors came as the Government also issued a further warning that even small amounts of combustible ACM cladding fitted to existing buildings must be removed.

Fresh guidance from the Government’s expert panel revealed that some experts were mistakenly advising building owners that combustible ACM cladding could remain on high rise buildings when fitted to small parts or strips of the building envelope.

The guidance says: “We have become aware that some building owners have received advice that indicates that it is acceptable to leave small or partial amounts of ACM cladding on their buildings.

“Given the risk of fire spread posed by ACM cladding systems, the independent expert advisory panel’s view is that leaving any amount of ACM cladding on a building would continue to pose a hazard to both residents and firefighters in the event of a fire.

“The clearest way to ensure the safety of residents is to remove all ACM, including small or partial areas of ACM, and replace it with a safe material. This remains the most appropriate remediation solution.”

However, the Fire Brigades Union (FBU) said the new regulations did not go far enough, claiming the move was “designed for political convenience”.

Class A2 materials such as plasterboard, which has limited combustibility, will continue to be permitted under the new rules.

Firefighters are calling for only A1 materials, which do not contribute to a fire at any stage – such as metal, stone and glass – be allowed.

The partial ban on combustible cladding will not be applied retrospectively to buildings that have already had the panels fitted.

FBU general secretary Matt Wrack said: “These measures do not deal with the existing cladding on nearly 500 buildings across England where people live and work every day.

“The government’s proposals only apply to buildings over 18 metres high, plus hospitals, care homes and student accommodation, when they should apply to all buildings, whatever their height or use.

“They continue to allow A2 materials, when they should permit only the highest standard of A1.”

Mr Wrack added: “This announcement is designed for political convenience, not for thoroughgoing change. The failings in the fire safety regime are far wider than just the materials used. The whole deregulated system and weak guidance needs to be overhauled.

“Many residents of high rise residential buildings and firefighters wanted more comprehensive action taken against flammable cladding. This government has failed to deliver.”

A spokesman for Mr Brokenshire said: “We are saddened to see the response of the Fire Brigades Union. We consulted on this very important matter and indeed went beyond what was asked of us.

“These measures will save lives, and we are clear building safety is at the very heart of what Mr Brokenshire is doing.”

Source: Construction Enquirer / The Independent

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