Addressing the combustibles ban consultation – the burning issue! Banning the use of structural timber?

The Wood Technology Society
,
20 May 2020

WTS Board member John Park explains and discusses:

 

CLT Apartment fire test at National Research Council Canada – follow this link

 

The headline in the architectural press on April 20 proclaimed: “Big names line up to defend timber buildings against proposed fire-safety 'ban.' Glenn Howells Architects, Waugh Thistleton and developer Urban Splash are lobbying the government not to ban structural timber under proposed rule changes on fire safety.”

In light of the current covid-19 situation, the UK Government has extended to 25th May 2020 the consultation for the review of the ban on the use of combustible materials in and on the external walls of buildings.  Here is the link:

https://www.gov.uk/government/consultations/review-of-the-ban-on-the-use-of-combustible-materials-in-and-on-the-external-walls-of-buildings

Having been roundly criticised for its lack of action following the Grenfell Tower fire, the Government is, no doubt, wishing to be seen to be addressing that criticism and making amends for any lack of action. The unfortunate consequence of that is that this consultation is fraught with implications, especially for timber, which go somewhat beyond building construction.

In consideration of this consultation, it is not difficult to draw the conclusion that the objective of Government is clearly to further extend its range rather than curtailing it with (almost!) no place for any subjectivity.  This is evidenced by the commonly occurring “Please provide details and evidence to support your answer”!  Question 7b of the consultation is perhaps the one glimmer of hope (for the timber industry) with even the possibility of a subjective response being considered (“… and why?”)!

Although earlier decisions were based on more than just simple non-combustible vs combustible, what logic there might have been applied (for some appropriate logic see below) was sufficient to rule out the adoption of sprinkler systems.  These were considered to be too costly an option (easier to just ban the use of combustible materials) but which would have resolved the issue for more than just, for example, the use of CLT within external walls.  

The aforementioned big names behind the use of CLT is admirable, but will they – notwithstanding the well-established capabilities in fire of CLT, and other large-dimension timbers and glulam being cited as evidence – be able to win the day with exemplary subjectivity founded on international adoption and fervent belief? Banning the use of wood within external walls would be a bad/wrong/illogical decision wrapped up as it was with choices which had to be made for good reason.  When a Government desires to be seen as effectual in the face of such horrors as precipitated by Grenfell, they will be extremely reluctant to admit that they were wrong by reversing their earlier decisions.

As for earlier decisions, Government’s desire to be seen to be doing something in order to help mitigate climate change was at the root of Grenfell Tower being covered in flammable insulation in the first place.

The outcome is more than just a little ironical as Government is now choosing to ban the one material that was not implicated in the disaster but which can contribute to that climate change mitigation desire by reducing the carbon footprint of buildings! 

Other benefits to be had are the cost savings from speed of erection, reduction in cost of foundations with lighter superstructure, considerable reduction in the time required for second fix work (not to mention reduced on-site noise), reduction in construction waste which, all-in-all, with a CLT building (and other timber elements), would outweigh significantly the cost of installation of sprinkler systems.

Wood in construction, for long having had to contend with calumny beloved of competing materials sectors, is also having to contend with the vagaries of reverse spin; the following is from an article in Inside Housing (on or around 29 April 2020):

Proponents of CLT argue that its fire risk is limited – partly on the basis that the wooden slabs “char rather than burn” on exposure to fire.  But Dr Rory Hadden, a lecturer in fire investigation at the University of Edinburgh, said more research needs to be done to truly understand the risks associated with CLT.

“The key thing that I would emphasise is that charring is burning. The charring process itself produces flammable gases and they contribute to the burning within a space,” he told Inside Housing. “The timber is going to burn. It’s marketing speak to say anything else.

“In a non-combustible building, you have the fuel, the tables, chairs, which will burn in a way that is independent to the structure. As soon as you start putting a fuel load on the walls, the ceilings, it fundamentally changes how that compartment is going to burn. [So] timber is going to require a rethink of how we do these designs.”

The above comment on fuel load, walls and ceilings is somewhat spurious as it is most likely that the use of CLT in multi-storey construction would, when considered prudent, be in combination with plasterboard.  This combination of produce will effectively shield the CLT from fire for a known time period commensurate with the thickness of the plasterboard. 

(“Gyproc 12.5mm WallBoard fixed either side (that should more correctly be ‘each’ side, of course or, even better, ‘both’ sides!) of minimum 63mm x 38mm timber studs at 600mm centres creates a 30-minute fire rated partition to BS476: Part 22. Using different combinations of board and insulation, various system options are available with fire resistances of 30, 60, 90 or 120 minutes. Please refer to White Book C04 S11 P02 for more details.”)

The issue of wood and fire and charring – and that is indeed burning, or rather it is the result of burning including, as with all combustion, consequential off-gassing – are considered on the Wood Technology Society website in the piece ‘Wood and Fire – and some food for thought’ to be found at the bottom of the ‘Wood as a Material’ pop-down list under ‘All About Wood’.  The September 2018 TTJ post-Grenfell Talking Timber article ‘Wood is not the issue’ is an opinion piece on the proposed banning of the use of wood within the external walls of medium-rise construction.

Of course, it is not just the architects addressing this issue with Government as The Confederation of Timber Industries has already made representation at 10 Downing Street.  Will they take heed? Apparently, there is some evidence that the outcome of such consultations can be influenced by weight of numbers which if you believe all you hear is what influenced the Government’s decision to ban combustible materials not just on but in external walls.

So, what is our next step?  Although this may not come to your attention before the consultation closing date, if everyone within the timber trade and industries were to drop their MP a line to point out all that would be wrong with banning the use of structural timber in the external walls of buildings, you never know it might even get some airing in the House, to bring sense to this discussion in order for Government to make logical decisions to put in place a sound Bill that takes into account environmental/business/economic considerations for a safe and prosperous future.

It is also rather ironical that at the same time as the UK Government is looking to hog-tie the advancement of CLT in multi-storey construction many other countries around the world are embracing the material and carrying out intensive testing to confirm its capabilities.  This from FPInnovations in Canada:  http://blog.fpinnovations.ca/blog/2020/05/13/fire-performance-of-mass-timber-construction-continuous-testing-confirms-their-fire-safety-attributes/

Use it as evidence when you write to your MP!