How to Build with CLT
Cross laminated timber is an innovative build material that can produce airtight, well-insulated homes that can be erected and made weathertight in days. So why, asks Allan Corfield, aren’t more UK self-builders using it?
Cross laminated timber, commonly known as CLT or crosslam, is a precision engineered building material that, despite a raft of practical and ecological benefits, is yet to be widely adopted by the UK self-build market. Growth has, however, been strong in the commercial sector, and it is likely that you have seen a building that features CLT: many modern schools, supermarkets, galleries and residential blocks use CLT for the superstructure. Developers here recognise CLT’S weight-to-strength ratio, low carbon footprint, speed and ease of construction — all features that should appeal to the self-builder, yet take up in the residential market has been comparably slow. However, there have been a number of award-winning self-builds in the UK featuring CLT — including Adam Knibb Architects’ Hurdle House, which won Best Contemporary Renovation/ Extension in The Daily Telegraph Homebuilding & Renovating Awards 2017, and the RIBA Award-winning Strange House ( below).
What is CLT?
The idea of stacking timber planks (known as lamellas) together to create a construction system can be traced back to German engineer Julius Natterer. He developed a system known as Brettstapel, which originally used nails to secure the wood in place (and now uses wooden dowels). This is still widely used in Austria and Germany and can be seen as a precursor to CLT, which developed out of academic and industrial efforts in the 1990s. It differs from Brettstapel in that it uses high grade timber stacked in a cross pattern to provide structural strength across two axis, rather than stacking in a single direction. CLT is formed of kiln-dried spruce or pine boards which are laid on top of each other at 90° (three, five, seven or nine layers depending on structural requirements), coated with a layer of polyurethane adhesive and subjected to immense hydraulic pressure to create large, stiff, dimensionally stable panels.
A Solution for a Tight Site This award-winning 75m2 self-build, designed by the architect/owner Hugh Strange of Strange Architects for a tight London plot, was built using CLT. The panels, from Eurban, have been exposed internally and given a whitewash finish.
Allan runs Allan Corfield Architects, which he set up in 2009. He is an expert in designing high-performing, energy-efficient homes. Allan Corfield