Lisø PhD Dissertation Manuscript - NTNU

Concluding remarks and further work
Untreated wood cladding that is properly ventilated and drained has a relatively long
lifetime even in harsh climates. A high-performance cladding is to a large degree
ensured if the principle of two-stage tightening is applied. Still, the lifetime of the
cladding is strongly dependent on the climatic impact on site. Preservative measures,
both surface treatment and impregnation, is used to enhance the lifetime of the
material. The presented national map of climate index distributions allows for
geographically differentiated guidelines on protective measures in the form of
impregnation, surface treatment or precautions in design of wooden structures. The
map will be used as an important instrument in the continuous development of
Norwegian technical guidelines for wooden building enclosures (e.g. the SINTEF
Building Research Design Sheets, see Lisø et al., 2005), allowing for climate
differentiation in both protective design and preservative treatment of wood.
Extended use of climate-differentiated preservation can contribute to a reduction of
the economic and environmental costs associated with preservative measures. The
opportunities for both prolonged maintenance intervals and extended use of
environmentally friendly wood preservatives in different climates should be subject to
further investigations.
The quantitative connection between wood decay rates and climatic impact should
also be further investigated. The moisture transfer mechanisms of wood are highly
influenced by the surrounding climatic conditions. Field- and laboratory
investigations are needed to further improve the reliability of the index for Norwegian
climatic conditions, including measurements of decay rates in different climates and
in different types of wood. Important issues to be considered are the low temperature
limit for growth in wood decaying fungi in evidence in Norway, and appurtenant
observed growth rates to temperature.
The built environment is experiencing extensive degradation and damage every year
due to climatic impact. Projected changes in climatic conditions will further enhance
vulnerability within the construction industry and the built environment (Lisø et al.,
2003b; Lisø, 2005). Climate change can increase the risk of decay of wood structures.
Climate indices allowing for quantitative assessment of building enclosure
performance or decay potential may be an important element in the development of
adaptation measures to meet the future risks of climate change in different parts of the
world. This and other indices, with established quantified relations between climatic
impact and material behaviour or building performance, can be used as a tool for
evaluation of changes in functional requirements or decay rates due to climate change
under global warming incorporating data from regional- and local-level climate
change scenarios as indicated in this paper. The presented work represents a first step
towards establishing such measures. Thorough analyses of projected future climate
index values, including assessment of uncertainty ranges, will be published in due
course.
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