Designing and building for longer life

Results from the research project WoodBuild have made it easier to calculate the lifetime of wooden structures and design the building envelope in a moisture-proof way. Now it is important that architects and structural engineers apply the new calculation models, according to Jöran Jermer of SP Technical Research Institute of Sweden.

WHEN RESEARCH PROJECT WoodBuild was launched in 2008, its focus was on increasing and disseminating knowledge, know-how and expertise on moisture-proofing and, from a durability perspective, on sustainable building in wood. The aim was to strengthen the competitiveness of wood as a construction material.

“Uncertainty surrounding the lifetime issue has caused many decision-makers to avoid wood,” says Jöran Jermer, civil engineer and head of the department for biobased materials and products at SP Technical Research Institute of Sweden.

“Those involved in WoodBuild have thus worked to develop methods and engineering tools that can be used for the practical planning and design of wooden structures, with a focus on moisture-proofing and lifetime,” explains Jöran Jermer.

WOODBUILD HAS BEEN a collaborative project primarily between SP Technical Research Institute of Sweden and the Faculty of Engineering (LTH) at Lund University. The work has been divided up into four research areas: methodology for lifetime calculations, exposed wood in the building envelope, wood outdoors above ground, and the resistance of wood and wood-based materials to biological attack.

The lifetime of a wooden structure depends on its exposure, i.e. geographic location, local climate, rainscreening, distance from the ground, detail design, how it is used and maintained, and the material’s resistance to fungal attack. It is, for example, well known that impregnated pine sapwood has greater durability than larch heartwood, which in turn is more durable than the sapwood of all other wood species.

Similarly, there is a risk that wood in the building envelope may be subject to microbial attack due to exposure, and here the factors include the outdoor and indoor climate, ventilation and the resistance of the wood material or wood preservation treatment to such attacks.

Research within WoodBuild has focused on increasing our understanding of how wood is exposed and how well the material is able to resist biological attacks. The new and groundbreaking achievement is to quantify the contributions from exposure and the material’s resistance and develop methods for calculating the expected lifetime of a structure and for designing a moisture-proof building envelope. The results have been summarised in two guides: Moisture-proof design of weatherscreening building components with moisture-sensitive materials (LTH Report TVBK 3065) and Durability of outdoor wood above ground (LTH Report TVBK 3066).

“The guides break new ground and are incredibly valuable. They serve as a tool and provide the engineering know-how that was previously lacking in wood construction, when it comes to moisture-proofing and lifetime aspects,” states Jöran Jermer.

THE RESULT OF WOODBUILD is that it is now easier to forecast the lifetime of a wooden structure and to design the building envelope for good moisture-proofing. But according to Jöran Jermer, a great deal of development work still remains to be done.

“It is my hope that planners, architects and structural engineers will use the knowledge that has come out of WoodBuild and apply our calculation models instead of ‘doing what we’ve always done’. It’s also important to receive feedback in order to develop and improve the models for practical application.”

TEXT: Katarina Brandt

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