Building enclosure and moisture management of mass timber construction

The building enclosure system separates the interior environments from the exterior environment, protects the structure from moisture and other environmental elements, and is a key passive design element of a durable, energy-efficient building. Therefore, the proper design and long-term performance of the building enclosure is critical to the sustainability of mass timber buildings

FPInnovations’ Building Systems team has been pursuing research in this field to increase knowledge and improve the performance of mass timber buildings with regard to energy efficiency and durability. Here are recently published documents on this topic.

Updated chapter on Building Enclosure in the 2019 CLT Handbook (Canadian edition)

Since the publication in 2011 of the first CLT Handbook, many buildings, from small to large using cross-laminated timber, have been built in Canada and the United States that helped FPInnovations and its partners increase their knowledge of building enclosure and durability.

Based on laboratory and field testing, and years of experience with CLT panels used in wall, roof, and floor applications, FPInnovations has recently published an updated version of its Building Enclosure chapter, which provides state-of-the-art information about building science guidance and best practices for the design and construction of building enclosures incorporating CLT panels.

A brief primer on relevant building code requirements and the building science of heat, vapour, air, and moisture control for CLT walls and roofs is followed by sections on CLT wall and roof designs and detailing. The final section covers strategies and solutions to address construction moisture, service moisture, and preservative treatment to ensure long-term durability. More information on how to get your copy is available here.

Two new InfoNotes on moisture management

Construction Moisture Management with Cross-Laminated Timber and Nail-Laminated Timber

Mass timber products including CLT and NLT, without use of preservative treatment or natural durable wood (e.g., yellow cedar), are intended for use under dry service conditions. Because prolonged wetting of wood may cause staining, mould, excessive dimensional change (sometimes enough to fail connectors), and even result in decay and loss of strength, construction moisture is an important consideration when building with all mass timber products including CLT and NLT.

Wetting during construction is mostly caused by exposure to liquid water sources, typically rain. On-site protection in wet weather, such as the rainy winter in a coastal climate, presents a large challenge for any construction including mass timber construction. In addition to wetting when the wood is in contact with liquid water, being a hygroscopic material, wood exchanges moisture with the surrounding air. Prolonged exposure to high humidity may also cause deterioration, such as excessive swelling and mould growth. The moisture content of wood should be monitored during construction with a focus on locations with high wetting potential such as joints and end grains, to provide more accurate information for making decisions about moisture protection and use of forced drying.

FPInnovations’ N8E InfoNote gathers all important information for planning, strategies for on-site moisture management, and remediation for your mass timber projects. The document can be downloaded here.

Concrete topping and construction moisture

FPInnovations recently conducted a laboratory test to investigate the potential wetting of CLT from the pouring of concrete topping, and the effectiveness of a water repellent coating and membranes in preventing such wetting. The test was performed on 3-ply CLT specimens with moisture pin-type sensors pre-installed to measure wood MC in the top surface, on which a concrete topping was poured.

The test showed that “Wet CLT” continued to dry after the pouring of concrete toping, while results from the “Dry CLT” specimens suggested that the moisture from the concrete topping did not greatly wet the CLT below, and pre-installing a continuous membrane reduced the MC of the CLT below.

More information on this project can be found in FPInnovations’ N9E InfoNote (available soon).

For more information on moisture management of mass timber buildings, please contact Jieying Wang, researcher in FPInnovations’ Building Systems group.

More InfoNotes from the Building Systems group are available here.

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