Timber Homes: Thinking big with wood

As the world’s oldest construction material timber had somewhat fallen out of fashion but in recent years it has staged a spectacular come back with an increasing number of developers trying it on for size. So is it going to be the next big thing or it is just a fad? By Michelle Gordon

Timber has long been a material of choice in Scotland where 70% of new-build homes have timber frames but it accounts for just 15% to 20% of the market share in England and Wales where bricks and masonry products have reigned supreme.

However in the last couple of years the oldest construction material known to man has started to take centre stage in an increasing number of developments and its use is predicted to continue growing.

“The growth that we are experiencing is considerable,” said Alex Goodfellow, group managing director of Stewart Milne Timber Systems. “The level of enquiries that we are getting is up 40 to 50% on two years ago.”

For those within the timber sector the growth of the industry comes as no surprise. As construction output picks up post-recession and housing demand continues to outstrip supply, timber ticks all of the boxes for a speedy, sustainable, cost-effective build.

“The market has really, really grown in the last couple of years in timber frame as the house building industry has recovered. We have grown because we can meet some of the challenges that our customers are having at the moment and have had in the last couple of years,” said Goodfellow.

“As the country has come out of the recession and all of the things that recession brings, we have been provided with this great opportunity to build more homes but the challenges are that we don’t have enough people, we don’t have enough resources beyond building sites, and we have found that some of the materials are not available or costs have gone up significantly in the last couple of years, so a lot of people have turned towards timber frame.

“When customers look to timber frame they are looking at something that may not have been their primary choice in the past but it is something that they are not unfamiliar with; it is something that is tried and tested, something that is reliable and it is available.”

You can build more quickly with timber frame says Goodfellow, with offsite manufacturing also enabling greater quality due to factory conditions. The fact that the frames are produced in a factory also means there is less activity on site meaning less noise and disruption for nearby residents, less construction waste and a reduced risk of accidents.

While the UK Government has pulled the plug on its targets for zero carbon homes, the European Union’s Energy Performance of Buildings Directive still stands, requiring all new buildings to be nearly zero-energy by the end of 2020 and timber’s green credentials have been a strong driver for its increased use.

“As the housing market has been slightly unleashed again developers are seeing a need to build quickly and there is a bit more of a churn in the market through incentives such as Help to Buy. More and more developers are turning to timber frame to deliver their projects more quickly,” said David Hopkins, executive director of the Wood for Good campaign.

“[Timber is] naturally low carbon so the increase in the manufacturing base across the whole timber industry doesn’t come with huge increases in emission and energy demand which it does in all other sectors if you have an upturn in brick production or steel or car production or any other sector it also comes with a huge surge in the power demand. Timber is a very low energy input system so you can have big economic growth without huge energy demand and emissions output.

“It drives a lot of investment back into our forests so it is like a virtuous circle really, as we are only ever going to use sustainably grown materials which means for every tree cut down a couple more are planted. It drives investment back into those with all of the biodiversity and eco-system and ecological services that they provide.”

Timber is the only mainstream building material that is 100% renewable says Wood for Good, which last year launched its ‘Build with Carbon’ campaign aimed at demonstrating how increased timber construction can act as an effective emissions reduction and carbon storage mechanism, while helping to meet social need and driving vital investment into our forests.

Trees absorb carbon dioxide from the atmosphere through the process of photosynthesis, storing the carbon and releasing the oxygen. The carbon is stored thereafter in wood products and research shows that roughly one tonne of carbon is stored for every metre cubed of timber used.

According to Wood for Good, new-build homes in the UK could be effective carbon ‘banks’, capturing and storing nearly four million tonnes of CO2 every year if housing targets were met through timber-frame construction.

“The carbon is stored in the tree and then in the timber product,” explains Hopkins. “They represent carbon emissions which have been sequestered from the atmosphere and stored right there in the physical form of timber. So you could look at pieces of wood/timber and timber products/buildings as representations of sequestered carbon.”

“Concrete and steel production is responsible for 10% of all carbon emissions,” said Andrew Waugh, director at architects Waugh Thistleton, which has a history of delivering timber buildings. “Furthermore 64% of the carbon emissions from the production of building materials come from cement and clay.

“Any technology that means we are not using concrete, cement and steel in construction can have a massive impact on the reduction of global carbon emissions – particularly if the production of that replacement resource actually absorbs carbon during its lifetime.”

And timber’s green credentials don’t stop there. Timber performs well in terms of air tightness and thermal bridging making it extremely energy efficient and leading to reduced energy bills for residents.

“We are finding that timber is becoming more widely and commonly specified because its more cost efficiently able to achieve higher energy standards,” said Goodfellow.

Waugh added: “We’re also hearing from end users that it is far outperforming predictions on acoustic and thermal performances as well as air tightness meaning great homes as well as cost effective safe and sustainable building. For that reason we’re designing more residential buildings, and for more clients, in timber than ever before and we don’t expect that to change.”

In fact timber is the material of choice for the first phase of homes at the UK’s first eco town in North West Bicester. Lead developer A2 Dominion has opted to use Stewart Milne Timber Systems’ Sigma II Build system for all of the 393 zero carbon homes which will be built in phase one of the development over the next five years.

The system is manufactured offsite and enabled the homes, which reached high energy performance levels, to be built within five to seven days.

“Timber allows us to meet many of our objectives on this scheme, a fabric first approach, reducing the carbon content within the construction of the homes, locally sourced material and high thermal efficiency,” explained Steve Hornblow, project director for NW Bicester. “A traditional masonry approach was considered but the timber frame solution fitted much better with the aspirations of the scheme.”

A2 Dominion has been able to meet the challenge of reducing the amount of carbon used in the build by 30% through embodied carbon of individual materials and local material sourcing while residents of the energy efficient homes will benefit from reduced energy bills.

“Because it is manufactured offsite and erected onsite it takes less time to construct, reducing costs, environmental impact and building time, which is a particular benefit to being able to deliver zero waste landfill as part of the construction process,” said Hornblow.

The use of timber frames has also helped to speed up the build process. “It has enabled us to speed up construction unhampered by weather conditions,” said Hornblow. “Homes have been made watertight in just a few weeks rather than months with traditional construction so we were able to continue working all through last winter regardless of weather.”

There are limitations, however, to what can be achieved with timber frame, which can’t go higher than seven storeys, but cross laminated timber (CLT) is taking building with timber to whole new heights (literally).

Work is currently underway on a 10-storey residential building in Dalston Lane, Hackney, which will become the tallest of its kind in the UK.

More than 3,000m3 of timber will be used making it by volume the largest CLT project globally and the building will comprise 121 units over 12,500sqm and over 3,460sqm of commercial space. For the architects Waugh Thistleton, CLT engineers Ramboll and developer Regal Homes, the most exciting aspect of the project is the sheer size of the structure.

“The height and size of the Dalston Lane building shows how versatile CLT is, as well as its potential in leading the future of sustainable construction,” said Ramboll director and CLT expert Gavin White. “We have been working on CLT projects for over 10 years now, so it’s heartening to see Hackney actively encouraging CLT construction, and we look forward to completing what will be a landmark building.”

Dalston Lane’s external, party and core walls, floors and stairs will be made entirely of CLT and Ramboll’s CLT experts have calculated that the building will save 2,400 tonnes of carbon, compared to an equivalent block with a concrete frame. There were many reasons for using cross laminated timber to construct the tower block said Waugh.

“Always first and foremost in our mind is to build sustainably. Housing is the most pressing challenge to the construction industry of this generation, but if we don’t stop to think about how we meet the challenge with responsibility to the environment then we simply push the next catastrophe down the line for our children to address.

“CLT answers this question ably by using a sustainable, replenishable resource, reducing carbon emissions that might otherwise be generated by building in concrete and providing an economic imperative to grow trees that lock in carbon absorbed during their lifetime – a process called sequestering. Including for sequestered carbon, we believe the construction of the building may even be carbon negative.

“Following on from that, we were able to show to our client the benefit of a supportive local authority when an approach to sustainability rises above the mere box ticking approach.

“More prosaically, building over the safeguarded routes for Crossrail and close to HS1 meant we also needed to reduce the weight of the building to an absolute minimum. Once again, building in timber was integral to the delivery of the project in this regard.

“The fact that timber makes better quality homes quickly and cheaply is a fabulous fringe benefit.”

CLT tower blocks are by no means commonplace in the UK but the method is growing in popularity as people realise just how versatile timber can be. Ramboll has previously completed an eight-storey student residential building from CLT at the University of East Anglia while Waugh Thistleton’s portfolio includes the nine-storey Murray Grove, which was completed in 2009 on behalf of Telford Homes, and was commissioned by Metropolitan Housing Trust.

“Since then [2009] there has been a steadily growing interest in the technology, particularly in Hackney (also home to Murray Grove) where the local authority has been very supportive of the approach due to its sustainable credentials,” said Andrew Waugh, director at Waugh Thistleton.

“Within a mile or two of Murray Grove there are at least four timber buildings that are five storeys or more and there are other buildings being built all over the UK of varying scales in structural cross-laminated timber and not just for housing. A whole campus of large-scale timber office buildings is being built in Oswestry in west London as we speak.”

Offsite fabrication has been the “Holy Grail” since the Egan Report said Waugh but it had always felt “frustratingly out of reach” on large projects. “Working in CLT feels a bit like a new dawn in that regard, straight from computer to saw mill and delivered to site flat packed and ready to erect with tiny construction tolerances meaning you can procure your windows at the same time as you order your external wall.

“We’ve even recently produced parts of a building with the external wall completely prefabricated through to the outer cladding on a constrained urban site. Prefab no longer means standard, orthogonal boxes or nothing.”

While CLT allows developers to build taller structures it offers the same benefits and green credentials as timber frame. “It’s necessary to remember that height isn’t the most important thing,” said Waugh. “There are some 500 CLT buildings in the UK, and the true value of these residential schemes is in helping meeting the national housing crisis – without increasing our carbon pollution.”

Both Waugh and White agree though that education is still an issue with many people both inside and outside of the construction sector being ignorant of the possibilities of building with timber.

“I think we need to educate people more about what can be achieved with timber engineering,” said White. “We can go tall; we can create amazing long-span structures and great education environments, enable quick construction times and ensure low embodied carbon. We just need to get the message out to more people so that they can experience this for themselves.

“The problem of providing housing in the UK is not going to go away and it’s not going to be solved over night. We in the construction industry must aspire to address this in a way that does not push other challenges – like climate change – down the line for others to deal with.

“That said, we’re not naïve enough to ignore that the construction industry is not sustainable unless it thrives economically. Timber has benefits in terms of cost and speed to add to its sustainable credentials. It seems like a no-brainer to us and to the increasing people that read the evidence, thus more will start to make the switch.”

This article first appeared in the October/November 2015 print edition of Housing magazine. Photo: Homes being constructed at NW Bicester