Effects of Climate Change on the Moisture Performance of Tallwood Building Envelope

Maurice Defo,Michael Lacasse

doi:10.3390/buildings11020035

Abstract

The objective of this study was to assess the potential effects of climate change on the moisture performance and durability of massive timber walls on the basis of results derived from hygrothermal simulations. One-dimensional simulations were run using DELPHIN 5.9.4 for 31 consecutive years of the 15 realizations of the modeled historical (1986–2016) and future (2062–2092) climates of five cities located across Canada. For all cities, water penetration in the wall assembly was assumed to be 1% wind-driven rain, and the air changes per hour in the drainage cavity was assumed to be 10. The mold growth index on the outer layer of the cross-laminated timber panel was used to compare the moisture performance for the historical and future periods. The simulation results showed that the risk of mold growth would increase in all the cities considered. However, the relative change varied from city to city. In the cities of Ottawa, Calgary and Winnipeg, the relative change in the mold growth index was higher than in the cities of Vancouver and St. John’s. For Vancouver and St. John’s, and under the assumptions used for these simulations, the risk was already higher under the historical period. This means that the mass timber walls in these two cities could not withstand a water penetration rate of 1% wind-driven rain, as used in the simulations, with a drainage cavity of 19 mm and an air changes per hour value of 10. Additional wall designs will be explored in respect to the moisture performance, and the results of these studies will be reported in a future publication.

Highlights

Tall wood buildings have been and are being constructed in many jurisdictions across Canada
The results showed that the synthesized weather data based on the dry bulb temperature predicted the hygrothermal conditions inside the wall very to the original regional climate model (RCM) weather data, and there is no considerable advantage in using the other two weather data groups
The approach described in the Guideline on Design for Durability of Building Envelopes [22] was used to assess the hygrothermal performance of massive timber walls under historical and future projected climate loads

Summary

Introduction

Tall wood buildings have been and are being constructed in many jurisdictions across Canada (e.g., the Brock Commons tall wood building at the University of British Columbia, Vancouver and the Origine tall wood building in Quebec City). The wall assemblies are designed to ensure durability in the presence of moisture, energy efficiency, fire safety and noise control. In cold, heating-dominated climate zones, the use of exterior insulation is the preferred thermal design approach [1,2]. Massive timber wall assemblies are comprised of cladding, a drainage cavity, insulation, an air barrier and water-resistive barrier, and the cross-laminated timber (CLT) panel. The use of vapor-permeable insulation is recommended to allow outward drying of the CLT if it is initially wetted or if there is water penetration due to deficiencies. There is no need for a vapor barrier at the interior of the assembly, as is the practice for wood frame construction, since the CLT panel provides sufficient outward vapor resistance. The material and thickness of the insulation depend on the climate zone in which the building is located

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