Project contact is Erol Karacabeyli at FPInnovations
To support NRCan's Tall Wood Building Demonstration Initiative, FPInnovations developed and published the 2014 Edition of Technical Guide for the Design and Construction of Tall Wood Buildings in Canada. More than 80 technical professionals comprised of design consultants and experts from FPInnovations, the National Research Council, the Canadian Wood Council and universities were involved in its development. The Guide has gained national and worldwide reputation as one of the most complete and credible documents helping to introduce to the design and construction community, and Authorities Having Jurisdiction the terms "Mass Timber Construction" and "Hybrid Tall Wood Buildings".
Since the publication of the First Edition, a number of tall wood buildings have been designed and constructed. Substantial regulatory changes are expected to happen based on the experience obtained from the demonstration initiative and the extensive research that has taken place domestically and internationally since the publication of the First Edition. These developments highlight a need for the Guide to be updated so that it aligns with efforts currently underway nationally and provincially and continues to lead in providing the design and construction community technical insight into new opportunities for building in wood.
The First Edition of the Guide helped to focus the efforts of the early adopters who participated in NRCan's Tall Wood Building Demonstration Initiative. Updating and aligning the Guide with the release of the new National Building Code of Canada and the Canadian wood design standard (CSA O86), and sharing the experiences gained from tall wood buildings built since the First Edition, will not only continue to expand the base of early adopters, but also help to move aspects of mass timber and hybrid wood buildings into the mainstream.
Project contact is Paulo Tabares at the Colorado School of Mines
Cross Laminated Timber (CLT) is a mass timber material that has the potential to expand the wood building market in the U.S. However, new sustainable building technologies need extensive field and numerical validation quantifying environmental and economic benefits of using CLT as a sustainable building material so it can be broadly adopted in the building community. These benefits will also be projected nationwide across the United States once state-of-the-art software is validated and will include showcasing and documenting synergies between multiple technologies in the building envelope and heating, ventilation and air conditioning (HVAC) systems. However, there are no such studies for CLT. The objective of this project is to quantify and showcase environmental and economic benefits of CLT as a sustainable building material in actual (and simulated) commercial buildings across the entire United States by doing: (1) on-site monitoring of at least four CLT buildings, (2) whole building energy model validation, (3) optimization of the performance and design for CLT buildings and (4) comparison with traditional building envelopes. This knowledge gap needs to be filled to position CLT on competitive grounds with steel and concrete and is the motivation for this study.
Unlike other solid wood panel systems, ICLT panels are manufactured without the use of adhesives or fasteners. Wood members are connected with tongue-andgroove joints within a given layer and with dovetail joints across layers. This reduces cost and allows ICLT panels to be disassembled at end of life to be repurposed in the building material supply chain. In addition, ICLT panels provide a means to utilize lumber from trees killed by mountain pine beetle.
Durability is critical for sustainable construction, and avoidance of moisture accumulation in wood structural members is essential for long-term performance. Little work has been done specifically on hygrothermal performance of massive timber construction.
The objective of this research is to identify building envelope design and construction practices for robust hygrothermal performance of ICLT walls in multiple U.S. climates.
This report provides an overview of major changes occurred in the recent decade to design and construction of the building envelope of wood and wood-hybrid construction. It also covers some new or unique considerations required to improve building envelope performance, due to evolutions of structural systems, architectural design, energy efficiency requirements, or use of new materials. It primarily aims to help practicioners better understand wood-based building envelope systems to improve design and construction practices. The information provided should also be useful to the wood industry to better understand the demands for wood products in the market place. Gaps in research are identified and summarized at the end of this report.
Project contacts are Shiling Pei (Colorado School of Mines) and Samuel L. Zelinka (Forest Products Laboratory)
This project will generate three benchmark data sets for multistory CLT building moisture performance in different climate zones. Data will include moisture contents at key wood components and high moisture risk locations throughout the buildings. A relatively simple, but fully validated, numerical model for analyzing similar building moisture performance will be recommended. These results will be useful for structural engineers and architects to accurately consider moisture in their design of mass timber buildings.
Borate can be a potential candidate to protect building envelope components from biodegradation as it has low toxicity and can penetrate wood without pressure treatment, even in the refractory species commonly used in construction industries as structural components. In this research, wood moisture content, grain direction, formulation and species that affect the diffusion of borate in refractory species were investigated. Two highly concentrated formulations were applied and a novel approach (borate bandage) was used to keep the preservative on the surface and enhance the diffusion by reducing surface drying. From ANOVA test for different diffusion periods and depths of penetration, it was found that grain directions and moisture content are significant factors. A mould test was performed, the diffusion co-efficients were calculated and some recommendations were made about the quantity required to protect a specific volume of wood considering the distance moved by diffusion and volume treated in different directions.
Cross-laminated timber (CLT) is a type of mass timber panel used in floor, wall, and roof assemblies. An important consideration in design and construction of timber buildings is moisture durability. This study characterized the hygrothermal performance of CLT panels with laboratory measurements at multiple scales, field measurements, and modeling. The CLT panels consisted of five layers, four with spruce-pine-fir lumber and one with Douglas-fir lumber. Laboratory characterization involved measurements on small specimens that included material from only one or two layers and large specimens that included all five layers of the CLT panel. Water absorption was measured with panel specimens partially immersed in water, and a new method was developed where panels were exposed to ponded water on the top surface. This configuration gave a higher rate of water uptake than the partial immersion test. The rate of drying was much slower when the wetted surface was covered with an impermeable membrane. Measured hygrothermal properties were implemented in a one-dimensional transient hygrothermal model. Simulation of water uptake indicated that vapor diffusion had a significant contribution in parallel with liquid transport. A simple approximation for liquid transport coefficients, with identical coefficients for suction and redistribution, was adequate for simulating panel-scale wetting and drying. Finally, hygrothermal simulation of a CLT roof assembly that had been monitored in a companion field study showed agreement in most cases within the sensor uncertainty. Although the hygrothermal properties are particular to the wood species and CLT panels investigated here, the modeling approach is broadly applicable.
The role of the Building Envelope team in this project is to assess whether alternate wood-based building envelope solutions developed by the Fire Team to meet the fire provisions of NBC 2010, also meet NBC Part 5 requirements relating to the protection of the building envelope from long term degradation due to uncontrolled heat, air, moisture and precipitation (HAMP) ingress into the building envelope of mid-rise buildings.
In a process of consultations with stakeholders, including the Canadian Wood Council (CWC), FPInnovations, and consultations with NRC’s Fire and Acoustics teams, specifications were developed for 2.44 m x 2.44 m wall specimens that would be investigated for hygrothermal performance.
Fifteen structural composite lumber (SCL) products including laminated-veneer lumber (LVL), laminated strand lumber (LSL), oriented strand lumber (OSL), and parallel strand lumber (PSL) provided by Boise Cascade, LP, West Fraser, and Weyerhaeuser were tested for moisture-related properties in this study, also covering four reference materials: 16-mm Oriented Strand Board (OSB), 19-mm Canadian Softwood Plywood (plywood), 38-mm Douglas-fir and lodgepole pine solid wood. Water absorption, vabour permeance, vapour sorption, and dimensional stability were measured with limited replication by following relevant standards for a purpose of assisting in improving building design and construction, such as hygrothermal modelling of building envelope assemblies, design for vertical differential movement, and on-site moisture management.