Two houses in England are striking a blow for UK-grown timber.
Shawm House, in West Woodburn, on the edge of Northumberland National Park, and Hieron’s Wood in Little Eaton, Derbyshire may not change the face of volume housebuilding but they will demonstrate some of the potential for using UK timber in construction.
Shawm is an old Northumbrian word meaning "to warm oneself" – an apt name for a highly-insulated house that will be enveloped in Scottish larch.
Originally it was planned as England’s first home-grown Brettstapel house, which attracted interest from the timber industry, but architect Dan Kerr of Mawson Kerr said the unknown for timber frame manufacturers raised the cost. Now the structure will be SIPs, comprising an injected cellulose insulation between two boards of OSB, strengthened with sections of home-grown softwood. SIPs and glulam trusses will form the roof.
"We could achieve the same U-value with SIPs as with Brettstapel and couldn’t justify doubling or trebling the cost," said Mr Kerr. The decision to use some sort of timber frame was arrived at jointly by the selfbuild client and the architects, and speed of erection was one of the advantages. Mr Kerr estimates that the three-bedroom house will be erected and wind and weathertight in less than a week.
"The site is isolated so having someone come in with a crane and erect the structure in one hit is better than someone block building over a few weeks," he said. "Also, the weather can be inhospitable so if we can get it up quickly, that’s great."
Externally, the house will be clad in larch, with the 25x120mm sections flowing from the walls over the roof, concealing gutters. Vertical, and possibly charred, sections will be used on the gable ends.
"We wanted to continue the aesthetic of the cladding on the walls, and keep it simple. It’s a traditional aspect in a barn but used in a contemporary way," said Mr Kerr.
As well as being informed by the rural setting, the house, with an 8x15m open plan living area on the first floor and bedrooms on the ground floor, reflects the neighbouring Grade II listed bastle house. These fortified dwellings, common in the Borders in the 16th and 17th centuries, had their living area upstairs and livestock area below so farmers could safeguard their stock from rustlers.
Around the same time as the building starts on site this summer, 200 miles south Derek Latham will also be starting work on his UK timber house – in sycamore.
The species grows like a weed in Mr Latham’s woodlands, which surround the site, so harvesting it has the dual benefit of providing a building material and improving the woodland management.
The existing literature does not present sycamore as a structural building material – it’s susceptible to rot, insect attack and shakes, it warps and it’s brittle. Testing is being carried out with the University of Derby, but Mr Latham, an architect, has also done his own research.
"Our understanding of British hardwoods in building derives from the 19th century, because that’s when they were used. In those days we were building breathable buildings so if I don’t let the sycamore get wet, it should be OK," he said.
He found that sycamore with a moisture content of less than 18% was not susceptible to rot or insect attack, and if it was dried to 12%, even if it became wet it was unlikely to exceed 18%.
A furniture maker who uses sycamore is also helping out: "He says as long as you have the right piece to start with, it won’t warp or shake so you need to stress grade it as you cut it," said Mr Latham. "You put it in the kiln, pack it and weight it and you should get 90% out as you cut it."
He plans to harvest the timber in winter, season it for six weeks, then place it in a kiln with dehumidifiers for around four weeks.
The sycamore will be used for the structural studding, floor joists, rafters, floorboards, the structural element of one hemp wall, and possibly ceiling boarding.
Boron-treated sycamore will also clad part of the exterior, "in the firm knowledge that in 10 years it will probably need to be replaced".
"A lot of it is suck it and see," said Mr Latham. "It’s truly experimental but it’s my own house so I can do it."
But while it is a small-scale experiment, it potentially has a wider reach. There’s a lot of sycamore in the UK and it has a low ecological value but grows almost anywhere so it could be grown in plantations, while also being cleared from natural woodlands.
"What I’m doing is a home-made exercise but if it indicates that sycamore is usable then perhaps it will lead the way to more industry-scale research and taking it seriously as a building material," said Mr Latham.
