A year of scrutiny

12 February 2019

Janet Sycamore, director of operations at the Timber Decking and Cladding Association says recent scrutiny must not undermine confidence in timber cladding

As we ease into 2019, we’ll remember 2018 as the year when cladding went firmly under the spotlight. The devastating fire at Grenfell Tower in June 2017 prompted a complex government consultation on combustible cladding throughout 2018. And we now know the outcome.

The key issue is the height of the building, with 18m being the critical figure. Yet, timber cladding on particularly tall buildings is a small market for the UK. It is not widely used in the high-rise building market and almost everyone we have spoken to about the regulation has confirmed that their cladding sales to the high-rise market have not been affected.

In fact, our members are reporting solid growth. However, the market is currently overcautious, often specifying fire treated timber when it isn’t mandatory. This may well settle down now that the changes to building regulations are clear.

The recent scrutiny, whilst important, must not undermine the confidence in timber cladding. It’s a highly appropriate and environmentally considerate material.

Levelling the playing field

Key changes in regulations followed the government consultation. Ironically, until now the four sets of building regulations in the UK have maintained less strict regulations than many other countries. The changes put us more in line with the international standard. Back to the 18m figure. If the upper floor level exceeds this height, the regulations now clearly state that timber cladding must not be used. Only non-combustible external cladding must be installed in this instance. It’s considered a sensible design precaution in the wake of lessons learnt from Grenfell Tower.

Interestingly, Scotland chose to go further than England and set the limit at 11m. Traditionally incorporating a higher level of fire safety in their regulations, the revised Scottish standards were developed by an expert committee including representatives from the timber frame industry, Edinburgh Napier University, the fire engineering department at Edinburgh University and the Construction Scotland Innovation Centre. The fire regulations in Wales and Northern Ireland are also likely to change in the near future although nothing is yet published.

So, let’s be clear on the new height limits for installation of timber cladding and how they compare internationally:

  • England: no timber cladding above 18m (six storeys) on buildings categorised as ‘high risk’ (residential tower blocks etc). Low risk buildings above this height must use flame retardant treated cladding.
  • Scotland: no building over 11m (four storeys) can be timber-clad unless the assembly can demonstrate fire safety through testing in accordance with BS 8414. Similar provisions apply to all entertainment and assembly buildings, irrespective of their height.
  • Germany: timber-clad facades are limited to heights of four to six storeys in most cases, depending on the construction detailing, use and proximity to a fire station. Internal sprinklers are mandatory.
  • Finland: residential buildings can only have timber facades up to six storeys high. Internal sprinklers are mandatory in buildings such as blocks of flats.
  • Sweden: the height limit for timber cladding is four storeys.
  • US and Canada: the height limit for timber cladding is six storeys.

“All these overseas countries are significant users of timber in construction and the regulations have been established after extensive fire testing,” said Dr Ivor Davies of Edinburgh Napier University.

“For example, Germany was part of a €5m research programme on the risks posed by timber facades. Fire regulations are not seen as a barrier to timber use in these regions. Far from it, in fact.”

Finland published some research that highlighted people felt safer in a timber framed and clad apartment block built to current fire regulations. It was considered safer than an all-concrete building of equivalent size, built to the previous regulations.

CE mark confusion

CE marking is not new for timber cladding. Under the Construction Products Regulation (CPR) it became a legal requirement for those placing timber cladding on the market in 2013.

But there’s still much confusion about when CE marking is required.

CE marking is mandatory for any construction product covered by a harmonised standard. The standard of relevance to timber cladding is BS EN 14915. Where the communication becomes potentially subjective is in article 5(a). The standard says that when the product is “individually manufactured or custom-made in a non-series process in response to a specific order” CE marking is not required.

Manufacturers must take care here. Are you supplying “individually manufactured” or “custom-made” material in a “non-series process”? The latter should be understood as the manufacture of goods without using standardised designs and assembly line techniques. Be clear with your definitions to ensure that you’re meeting the regulations correctly.

Product innovation

It’ll come as no surprise that western red cedar and larch continue to be the timber cladding species of choice. Loved for their natural beauty, these species are stable and offer natural durability against decay (heartwood only).

So, what could be better than highperforming, natural timber?

With growing interest in modified timber products, many more brands are coming to market. We’re seeing modified wood remodelled into benefit-rich cladding, with the use of intelligent technologies. This innovation is taking the timber cladding market to another level and is addressing the needs of many demanding customers. Modified timber can offer a consistent surface appeal, dimensional stability, improved weather resistance and factory coating capability.

Factory coating is an interesting consideration. Using a dimensionally stable product, coating performance is optimised and visual appeal enhanced. Coated on all four sides, there is no need for further work on site, saving both time and money.

Literally translated as “burnt cedar wood, the Shou Sugi Ban cladding product draws on the ancient Japanese art of charring timber to create a consistent surface appeal. The result – dependent on species and method of charring – is a charcoal-black, contemporary finish that can last for many years without maintenance. It’s important to work with a durable base species though. In Japan the process is only intended to create an inert surface finish to hide weathering stains. It does not improve dimensional stability, increase durability or change the fire performance of the cladding timber.

Having undergone an acetylation process, Accoya excels on durability. Offering a 50-year above ground guarantee and rated as durability class 1, that’s a big tick in the box.

Ideal for coating, James Latham offers Accoya cladding and business is good. The company confirmed that the market is very positive for modified timber. Both Sansin coated Accoya and its charred Shou Sugi Ban Accoya are “doing well”.

Meanwhile, Glenalmond Timber launched Abodo in the UK last year. Abodo is manufactured from thermally modified radiata pine. It offers reassuring stability, whilst it’s naturally durable, of low moisture content and consistent in colour. Abodo is also knot-free, which suits its contemporary use and makes it a popular choice with architects. A long service life that’s warranty-backed provides further confidence.

Incidentally, western red cedar is one of the best softwoods in terms of insulation. However, this is not relevant to external timber cladding because the cladding assembly has a ventilated cavity between the cladding and backing wall. This means that, in accordance with BS EN ISO 6946, the cladding and cavity have to be ignored when calculating U-values.

Bad practice, good guidance

Offering an independent inspection and mediation service, the TDCA experienced a worrying surge of bad practice complaints in 2018. The most common examples included: incorrect fixings, poor fixing methods, lack of provision for moisture movement and durability requirements. These are all poor practices that should never have happened.

The financial impact of bad practice can be costly in addition to the reputational damage. The timber cladding industry should work with TDCA CladMark accredited products and installers. Proactive cladding manufacturers should become CladMark accredited and have their high standards recognised.

Continuing to support the industry and communicate best practice, the TDCA is co-funding a new standard in collaboration with the TTF, Wood Campus, Wood Knowledge Wales and Canada Wood.

BS 8605-2 – the code of practice for timber cladding and the second part of BS 8605 – will give detailed guidance on installation practice providing a single, authoritative resource for all to follow.

Authored by leading cladding expert, Dr Ivor Davies, the planned publication is in 2020. Dr Davies is currently finalising the fire section of BS 8605, now that building regulation changes have been clarified. The BSI drafting committee for BS 8605-2 will soon meet to discuss the fire section in detail.

As the timber cladding market evolves to meet ever-demanding requirements, success will come from a forward-thinking approach. Quality must never be compromised for short-term gain. Long-term growth will come from continual education about best practice, new techniques and innovative products.

The TDCA is poised to support all parties in the timber cladding industry throughout 2019 and beyond.

Abodo cladding has been introduced to the UK by Glenalmond Timber
Shou Sugi Ban Accoya is selling well at James Latham
James Latham supplied Accoya with factory applied Sansin coating for this KFC outlet