A timber-framed future for UK housing: Donaldson Timber Systems

Brick-clad timber buildings using Donaldson's timber frame system

Why have Donaldson Timber Systems just invested £10m in their offsite timber-frame factory? Because they anticipate a big future for timber-frame housing in the UK. They’ve boosted their capacity and technical capabilities because – like many of the UK’s major housebuilders – they see timber frame as increasingly central to UK housing.

Donaldson Group provides a host of engineered timber services and products, including roof trusses, open web joists and I-joists among others. But it’s their timber-frame build systems – from Donaldson Timber Systems – that we’re focusing on here. John Smith, Technical Director of Donaldson Timber Systems, tells us all about them.

A future-focused, industrialised frame factory
The company has recently given an extensive refit to its factory in Oxfordshire. It is now fully geared up to deliver closed-panel timber-frame build systems at scale. “We have a new floor line and robotic wall line – all optimised to produce up to 5000 units per year, increasing our national capacity to 9,000 units per year,” John informs us.

Sigma II panels, complete with pre-fitted windows, being installed onsite.

Sigma II panels, complete with pre-fitted windows, being installed onsite.; © Donaldson Timber Systems

The investment in machinery and performance upgrades at the Witney site includes four timber processing centres and a new floor panel production line, offering customers a fully completed pre-glued floor cassette solution. The site has also installed the most advanced automated pre-insulated closed-panel wall production line in Europe.

The purpose of all this is to increase automation to improve efficiency and create additional capacity, all with less requirement for physically demanding roles, allowing us to hire a wider variety of people to work in our factories.

A turn towards timber for the biggest UK housebuilders
It’s clear that Donaldson are confident that timber expansion in the UK is inevitable. While Scotland has long dwarfed England as a market for timber frame – some 90% of its new houses are timber – timber is definitely on the up in England.

Of the total 214,000 new homes produced in the UK in 2019, 58,000 (27%) of them were timber frame, up from 25% in 2016.

The major players – including Barratt, Taylor Wimpey and Vistry – have all opened their own timber-frame factories within the last two years. Such a confident buy-in from the biggest UK housebuilders speaks volumes about the future of timber in England and Wales. Evidently they believe that wood is where it’s at.
And while the moves into timber frame by these volume housebuilders mean they are no longer Donaldson customers, John welcomes the fact that the volume of timber housing in England is set to grow.

“That Barratt – the UK’s biggest housebuilder – has invested heavily in timber frame is good news for the industry as a whole,” he suggests. “All the big builders have committed to a level of offsite production – partly due to the problem of skills shortages. And timber frame is a tried-and-tested, proven answer.”

Case study: Orchard Field
A sustainable development of 88 new houses in the village of Siddington in Gloucestershire, Orchard Field uses the Sigma® II system. There’s a mixture of 1, 2, 3, 4 and 5 bedroom homes, each meeting Association for Environment Conscious Building standards, which demand excellent construction and low energy consumption.

Brick-clad timber buildings using Donaldson's timber frame system

Orchard Field is a sustainable development
of 88 new properties in the village of Siddington near Cirencester, using Donaldson’s Sigma II frame.

The frames are 23.5cm thick and, once they are clad, the walls are a heat-saving 45cm thick. Other environmentally friendly features include ground-floor underfloor heating fuelled by air source heat pumps, the use of MVHR, small-bore pipes delivering rapid hot water to sinks and showers, solar panels and electric car charging points. This was the first venture in timber frame for developers Stonewood Partnerships. The development achieves near Passivhaus standards, but at the same time exceptionally low embodied carbon.

Alpha, Delta, Sigma II: three timber frames
Donaldson have three timber-frame, panel-based building systems: Alpha, Delta and Sigma II. All three are eminently suitable for low-to-medium rise house building and are fully compliant with Building Regulations for England, Scotland and Wales. All are high performing, factory-made, and are fully tested and technically supported.
Alpha is a traditional open-panel timber frame and has been a core product in the UK timber market for many years. It has been fully tested on large-volume housing projects and has the option of pre-assembled floor cassettes or loose joists, as well as engineered roof trusses or insulated roof cassettes.
Delta is the next step up in terms of factory-fitted features. It’s still an open panel but comes with insulation pre-installed. So it suits projects seeking to achieve an enhanced thermal performance level, and reduced site waste – a solution for customers keen to take advantage of more offsite manufacturing features. Similar to Alpha, it comes with the option of pre-assembled floor cassettes and roof trusses or insulated roof cassettes.

Donaldson timber factory offsite timber frame manufacture

Factory manufacture of the frames ensures a high degree of accuracy and quality.

Sigma II is what John describes as the “halo product”. It’s a fully closed pre-insulated panel, with the option of factory-fitted windows and higher levels of premanufactured value. It maximises the benefits of factory assembly and dramatically cuts down on onsite activity: it offers Donaldson’s highest level of building fabric performance, with excellent thermal performance and airtightness. The Sigma II build system uses only fully recyclable materials and very low levels of embodied carbon.

What customers want: sustainability and surety
There are two big selling points to Donaldson’s timber frame systems: the low embodied carbon and the third-party certification, both of which are becoming increasingly important to customers. All of their systems have STA Assure Gold and Robust Details accreditation – as well as ISO standards for quality, health and safety, and environment – while the Sigma II build system is also BBA and BOPAS+ approved – the latter providing the assurance of 60-year durability assessment and lending confidence from the insurance industry.
“We’re quite proud of the fact that we have pretty much every badge out there!” John enthuses. “Our systems are audited twice per year, which means we generally have at least one auditor at our factory every month. That’s in addition to our own in-house quality control. If it’s factory assembled and you didn’t have controls in place the industry would start to lose credibility.”

Given the new levels of scrutiny brought in by the Building Safety Act, with its emphasis on ‘the golden thread’, this degree of quality assurance is a significant part of Donaldson’s differentiation in the market.

“The offsite housing sector has unfortunately seen some large volumetric manufacturers entering administration in recent years but Donaldson Timber Systems will be celebrating its fiftieth birthday next year,” John states. “Longevity, durability and flexibility – these are all things that a panelised timber system can provide.”

Case study: Eynsham Road

Eynsham Road, Oxford, is a development for 8 apartments for Lifebuild Solutions Ltd, built using Donaldson’s Alpha build system. The site is located in multiple shared rear gardens of occupied houses, with restricted access. Donaldson Timber Eynshame Road Oxford

Using an offsite timber frame build system was key to the success of the project, vastly reducing the construction period, and in turn the disruption to neighbouring properties, as well as achieving both the bespoke architectural design and high thermal performance required.

Catering to the first-timers
For customers newer to timber frame, John suggests, training is a key part of the successful transition from building in brick and block to a more offsite based building system. “We have a full suite of CPD certified training modules for our customers and their sub-contractors, to help them realise the benefits of using a timber frame build systems as quickly as possible”.
At the same time, some of the forward-thinking regional private developers are increasingly keen on achieving near-Passivhaus levels of fabric performance. And housing associations, who are likely to own the building for longer, want future-proof buildings with the accompanied lower utilty bills for tenants. Donaldson’s Sigma II build system can achieve this level of performance and lower bills.
John also points out that Homes England promotes MMC through setting a target of 55% Pre-Manufactured Value (PMV) which is a measure of how much of the building is assembled in a factory and how much is done on site. Donaldson’s Sigma II build system achieves between 55% and 58% PMV.

Donaldson timber panel systems being installed by construction team

Timber panel systems can be quickly and efficiently installed, often by much smaller teams.

Helping customers count their carbon
Donaldson now have their own carbon calculator tool, measuring the embodied and sequestered carbon for all their build systems. Its outputs can include end-of-life carbon emissions for a cradle-to-grave assessment; and can provide comparisons with equivalent masonry builds. Its methodology is in line with the requirements of PAS 2050:2011 the RICS Whole life carbon assessment for the built environment standard.

What will really usher in the timber revolution?
“The Future Homes Standard is welcome but it doesn’t go far enough in terms of really pushing building fabric,” John says.
There are two things that the next government could do that would really make a difference, he suggests.

One is that the industry needs a secure pipeline of work. The current condition of the planning system is an impediment here. It requires proper investment and resourcing in order to ensure projects progress.
Secondly, embodied carbon needs to taken more seriously: both measuring it and setting limits upon it. “Other parts of Europe are already measuring embodied carbon and setting targets,” John points out.
“The UK isn’t going to get to net zero without firstly measuring and then reducing the embodied carbon of our buildings. That would be a key driver for timber use – a step change.”

This article is taken from Designing Timber issue 7

Many thanks to John Smith, Technical Director, Donaldson Timber Frames