Setting the standards for structural timber

Structural Timber Association board member and managing director for Kingspan Timber Solutions and Potton, Mark Stevenson answers self-builders’ queries on how to use structural timber, and why solutions are increasingly likely to be factory-built.

The Structural Timber Association (STA) has an objective to enhance quality through research and guidance, underpinned by the independently audited STA Assure Membership and Quality Standards Scheme. Having worked across all areas of construction for decades, we understand that for self-builders, property development is not a chosen career, it is much more than that – it is a personal mission which, more often than not, represents the investment of a lifetime. It’s therefore vital you make the right decisions, so why should you consider offsite manufactured structural timber?

What are the main benefits of building with structural timber?
With impressive green credentials, combined with cost and time efficiencies, structural timber systems are rapidly becoming the building material of choice – currently accounting for around 75 per cent of the self-build market. Advanced prefabricated systems such as closed panel timber frame, structural insulated panels (SIPs) and volumetric modular options are driving innovation in the timber industry – offering customers more choice than ever before.

Why is there a move to build homes offsite?
Offsite-manufactured structural timber systems have advanced greatly in recent years, offering self-builders cost, programme and performance assurances. The solutions are increasingly likely to be ‘factory-built,’ with greater levels of prefabrication as part of controlled manufacturing processes. If required, complete houses can be finished in the factory ready for onsite installation. Commonly in the self-build sector, the focus is towards panelisation, with doors and windows fitted as part of the manufacturing process. This and shorter construction timescales, better build quality and enhanced energy efficiency – vastly reducing on-going running costs for the life of the building – are compelling reasons to specify these solutions.

Why is factory manufacturing of systems the ideal solution for timber homes?
With standards for efficiency constantly ramping up, the construction industry as a whole has faced a real challenge in creating homes that achieve the actual predicted energy performance. What was an industry wide issue – achieving the actual energy performance as specified in the design brief, has been difficult to attain using traditional site-based methods. This issue has been overcome using a range of timber-based offsite technologies within a quality-controlled factory environment to create high performance low energy build systems. Manufacturing in factory-controlled conditions with stringent controls minimises waste, optimises quality and assures the performance of the building for its intended lifespan.

Does offsite manufacturing mean I have to have an off-the-peg design, or can it be made fully bespoke?
Absolutely not – from traditional cottages, to contemporary designer led architecture, structural timber solutions enhance design ambitions and deliver beyond expectations. The timber industry is no longer defined simply by the supply of timber frame kits – it is driven by intelligent and integrated construction solutions. The breadth of the product portfolio means that any cost, performance and design expectation can be achieved.

I have a difficult site, how can offsite timber help make things easier?
The range of technologies available for offsite manufacturing enable innovative hybrid solutions to be created which overcome almost all the problems that self-builders can face on challenging sites. Often, timber structures are thought as not being suitable for sloping sites, but the reverse is actually true. Prefabrication enables most of the work to be removed from site, and by employing advanced lifting equipment, we can overcome the challenging terrain and build much quicker than with traditional techniques.

When is offsite not suitable for a self-build?
When the customer wants a poorly performing, low value building – which in my experience is never!

Is it a lot more expensive than traditional construction?
Measuring cost is a complicated equation and when all factors are taken into consideration, structural timber solutions represent far greater value for self-builders. Here are a few points to consider:

  • The speed of construction achieved through the high degree of factory prefabrication enables a rapid build process, which is not adversely influenced by inclement weather. Should the self-builder be renting a property during the build, then the rental costs are vastly reduced.
  • Structural timber construction offers cost and programme certainty, making programming and budgeting more predictable than traditional site-based methods. Engineered timber systems means the entire superstructure is designed, supplied and constructed with a single point of responsibility – eliminating the risk of dealing with multiple suppliers.
  • Stringent factory quality controls enhance the manufacture of offsite buildings, delivering a high-performance building envelope, reducing the energy consumption across the lifetime of the home – saving substantial annual costs on utility bills.
  • Mortgage providers are given assurances through guaranteed build quality backed by warranties and accreditations and now consider structural timber as a mainstream construction method.

How can fire safety be assured in timber systems?
Fire safety is an essential Building Regulation design requirement for any building. In a completed building, the structure is protected from the effects of fire by internal plasterboard linings and external claddings. As structural timber systems are manufactured offsite, we have the opportunity to independently test the fire performance of the completed wall and floor elements. This testing enables finite assurances to be given to the self-builder of the structural integrity of the system in the event of a fire and reassures warranty providers that the system used meets, or in most cases exceeds the requirements of the Building Regulations in terms of means of escape and external cladding. Fire safety involves more than providing means of escape in the event of a fire – it also involves the impact your building project may have on neighbouring properties.

With the Fire and Rescue Service, Association of British Insurers (ABI), The Fire Protection Association (FPA), Health and Safety Executive (HSE) and Fire Engineers, the STA has developed a Site Safe Policy. A mandatory requirement of STA membership, the Site Safe Policy addresses the approach needed to mitigate fire risks.

Developed over many years to support STA members and provide the service that self-builder clients would expect of a professional building system provider – the policy is mandatory for members because it ensures they fulfil their CDM (Construction Design and Management Regulations 2015) duties in relation to fire safety.

Are regular builders ready to build timber homes using offsite methods?
Each year, the proportion of homes that are built using timber systems increases. In Scotland, structural timber is now the de facto build method and we see no reason that it won’t be the same throughout the rest of the UK as customers understand the benefits structural timber offers. I expect the number of builders who adopt the technology will also increase due to the chronic shortage of onsite trades.

Is there any legislation I need to be aware of as a client?
Yes, any build has to conform to building and health and safety regulations. This is an area where timber system manufacturers who are accredited under the STA Assure scheme excel. As the UK’s leading organisation representing the sector, one of the Structural Timber Association’s main objectives is to ensure our members meet current legislation and regulatory requirements.

Offering confidence to self-builders by promoting the differing levels of accreditation held by individual member companies, the STA Assure Membership and Quality Standards Scheme is recognised by six of the industry’s leading structural warranty and building control bodies – LABC Warranty, Premier Guarantee, Protek Warranty, Build-Zone, Selfbuild Zone and CRL.

This assessment has been developed to benefit both our members and construction clients, offering reassurances to the construction community that our members meet or even exceed current legislation and regulatory requirements. In addition, we enforce the industry leading initiative, Site Safe and provide all our members with access to the very latest health and safety training.

Mark Stevenson is STA board member and managing director for Kingspan Timber Solutions and Potton