Abstract
Cross-Laminated Timber (CLT) elements have had a growing popularity in recent years due to i.e. low carbon footprint, low weight and efficient construction time. However, the elements are sensitive to moisture and prone to organic growth if not treated properly or if used incorrectly. Roof slabs are particularly exposed, as they have a large area of exposure and the horizontal orientation doesn’t allow rainwater run-off. The efforts made to protect CLT-roofing elements by Norwegian contractors vary widely, as there are few guidelines and little long-term experience. A field study of CLT-roofs on existing buildings was conducted to investigate the conditions after some years in service. The study includes inspection and moisture measurements of CLT elements from the exterior side in 10 building projects 1-9 years old from two regions of Norway. The contractor of each project was interviewed in order to assess the extent of climate exposure and protection measures during construction. The results indicate a correlation between water content, building age and exposure level during construction. There is a clear indication that the drying time for built-in moisture in CLT roof constructions are slow. Keeping built-in moisture to a minimum is therefore paramount.
Highlights
IntroductionBackground and objective The use of Cross-Laminated Timber (CLT) elements in the Norwegian building industry has become increasingly popular in recent years due to i.e. low carbon footprint, low weight, and efficient construction time
The solution choices varied to some extent between the inspected roofs. 7 out of 17 inspected roof segments had PE-foil as a vapor barrier between the Cross-Laminated Timber (CLT)-element and insulation layer. 8 out of 17 used an asphalt-based membrane as a provisional, temporary roofing to protect the CLT-elements during the building phase, which functions as a vapor barrier during the operations phase. 2 out of 17 roof segments had a vapor open membrane between the CLT-elements and the insulation layer
The findings in this study, regarding moisture protection measures, are analogous to the results found in the literature: it is clear that a strategy for reducing the risk of built-in moisture is important for CLT-construction [10,11,12]
Summary
Background and objective The use of Cross-Laminated Timber (CLT) elements in the Norwegian building industry has become increasingly popular in recent years due to i.e. low carbon footprint, low weight, and efficient construction time. The widespread use of CLT-elements is relatively new in Norway, and studies have shown that there is a demand for clear and updated guidelines for using CLT-elements [1]. After the structural CLT shell is in place at a building site, it stands exposed to the elements for a period before the weather screen is in place, and moisture uptake from rain may accumulate if the CLT are not temporarily protected in some way. The efforts made to protect CLT-roof elements by Norwegian contractors vary widely, as there are few guidelines and little experience with potential consequences over time. A method for creating CLT Construction Guidelines involving the construction industry is demonstrated by Wahlstrøm [2], but the guidelines are not yet completed
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