Some of the most important new buildings to be completed in and around London are not oddly-shaped skyscrapers made of steel and glass, but highly-efficient low-rise buildings made largely of timber. After years of proven success in Europe, the use of structural timber, including CLT, glulam and other types of ply, is making inroads in major building projects in the UK and helping to increase sustainability and energy efficiency.
Plywood on Steroids
The primary material used in all of these structures is cross-laminated timber, an engineered wood product that's been used in Europe for decades, but which has had a slower uptake in the UK, US and Canada. Cross-laminated timber (CLT) is what Arup engineer Timothy Snelson calls "plywood on steroids," extra-thick layers of softwood which are laid with the grain running perpendicular to one another.
Standard plywood is made at a thickness of usually 6 - 12 mm (0.23 - 0.47 in), but CLT uses much fatter layers, resulting in thicknesses of 57 - 300 mm (2.2 - 11.8 in) with some "jumbo" versions as thick as 500 mm (19.7 in). The cross-layering of the wood adds stability, as with regular ply, but the greater thickness creates panels that are strong enough to be used structurally, without the need for reinforcing brick or concrete.
Timber absorbs carbon as it grows and emits very little, even when it is manufactured. The production of Portland cement, used for concrete, is responsible for 7 percent of carbon emissions worldwide, even before the concrete is mixed, transported and applied. Steel and glass also have comparatively much higher embodied energy.
The use of CLT also reduces the build time, in some cases by as much as 50 percent, and therefore the total emissions during construction. This is because the timber elements are delivered as prefabricated walls or modules, often referred to as "cassettes," which are then fit together quickly on site. Also, timber is a "dry" construction material; it doesn’t need time to dry out or cure, as with concrete or masonry fixings.
CLT makes use of soft woods that are fast growing and plentiful, such as fir and spruce, rather than hard woods, which take longer to grow and are harder to replace. The laminating of thick sheets turns this plentiful softwood into a structurally sound building material.
Kingsgate House, Chelsea, Horden Cherry Lee
The Kingsgate block of affordable housing in Chelsea by Horden Cherry Lee was completed in January of this year and, using mainly CLT, is the first-ever building to attain PEFC (forestry) certification. The Kingsgate building joins innovation and affordable housing with 43 units over seven floors. The build time was a fast 12 weeks and the overall weight was 14 percent lower than it would have been using concrete, which resulted in savings on foundations and delivery costs.
The timber for Kingsgate has all been PEFC-certified (Programme for the Enforcement of Certification), making this the first building in the UK, and possibly the world, with this type of recognition. The PEFC certification says that the wood products used in the building were deemed "legal and sustainable," meaning that all of the interim retailers and manufacturers who have handled the products are known to adhere to sustainability guidelines. The process sounds like a bureaucratic forest in itself, but it just means that the timber used can be traced to sustainable origins.
The energy equivalent of a Smart car
The building’s most notable energy-saving feature is its golden solar shutters. These vertical elements help shade the window openings, but the golden tone of the PV cells were designed to match the nearby brick of older buildings, a nice touch. The shutters generate 60 kWh of energy per day, providing 21 percent of energy required for the building and saving 14.5 tonnes of CO2 every year.
An exhaust air heat pump reduces energy needed for heating water by 47 percent, and high-value insulation reduces energy consumption by 70 percent compared to a building with traditional construction methods and materials. Architect Richard Horden also calculates that the whole building consumes around 250 kWh per day of energy, the same as driving a Smart car for an entire day. For each unit, the energy required is only around 5.8 kWh per day, the equivalent of driving a Smart car around for about half an hour.
Julian Study Centre, University of East Anglia, Pick Everard
On a campus of environmentally-conscious buildings, the new Julian Study Centre designed by Pick Everard claims to outdo even its campus mates, being "possibly the lowest-carbon building in the UK." The building is a combination of timber, steel and glass, with timber accounting for 95 percent of the structural material.
The pre-fabricated CLT components made for a more efficient and quicker build time as well as reducing the overall embodied energy of the building, which covers 2,000 square meters (21,500 sq ft) over 4 floors. The timber construction helped to reduce the air leakage to a rate that is 80 percent more efficient than the standard limit for UK buildings, according to the architects.
Even among the green campus of UEA, this building is the first to achieve a rating of "Excellent" in the BREEAM (Building Resource Establishment’s Environmental Assessment Method) accreditation scheme. The building also uses photo-voltaic panels, triple glazing and some recycled content.
More Timber Firsts
The William Perk Church of England Academy in North Ealing, London, by Fielden Clegg Bradley Studios now lays claim to being the largest timber-constructed building in the UK. Though it's not the tallest, that honor goes to the Stadthaus building in Hackney, East London, by Waugh Thistleton, one of a handful of "plyscrapers" going up in various locations around the world. The building by Fielden Clegg Bradley is larger in area, covering 25,000 square meters (270,000 sq ft). It too uses mainly CLT for its structure.
A new facility for Sky’s Osterley campus, for which full details are still under wraps, will be London’s first major commercial building constructed mainly of timber. According to Timothy Snelson of Arup Associates, the use of timber cassettes will mean savings on foundation materials, build costs, and energy consumption.
The new 4-story building will be completed in 11 months, as opposed to a projected 22 months using steel and concrete, and will be constructed using 12-meter (39-ft) panels of CLT and glulam (glue-laminated beams). It will also use various passive strategies for heating and cooling as well as innovative systems of rainwater harvesting.