The purpose of this research is to investigate what differences, if any, exist between the modeled energy consumption and building envelope performance of the Wood Innovation Research Laboratory (WIRL) building following eight months of in-situ data collection. The WIRL building was completed in July of 2018 by the University of Northern British Columbia (UNBC) and is located in Prince George, British Columbia. Built in partnership with the Province of British Columbia, the building was designed to meet Passive House standards, a building certification system that requires the building to have low energy input requirements due to high levels of thermal insulation and minimal air leakage. To ensure the building achieves the established energy use targets set forth under the Passive House certification system, a computer model of the proposed building design must be completed prior to the start of construction using the Passive House Planning Package (PHPP) software. Inputs to the model include envelope design, mechanical energy use, building location and airtightness value. Key outputs included the predicted annual heating demand (kWh/m2a), total primary energy demand (kWh/m2a), and air tightness of the building envelope (ACH@50Pa). Based on the final building design model and test results achieved following completion, the WIRL building was deemed to have met all Passive House requirements and certification was achieved. To complete on-going data collection of the in-situ performance of the WIRL building, temperature and humidity sensors were installed in two of the exterior wall assemblies and the building’s floor. In addition, gas and electrical energy use meters were installed to monitor the building’s energy consumption. The installation of all equipment was made possible by Forest Innovation Investment through their 2018/2019 Wood First Program.
Canadian Conference on Building Science and Technology
On tall wood buildings, mass timber elements including CLT, NLT, glulam, and other engineered
components absolutely need to be protected from excessive wetting during construction. This requirement precludes the use of many conventional cladding systems unless the building is fully hoarded during construction.
The building enclosure and façade of UBC Tallwood House consists of an innovative prefabricated steel stud rainscreen curtain-wall assembly that is pre-insulated, pre-clad, and has factory installed windows. Design of connections and air and water sealing of panel joints and interfaces was carefully considered given the tall wood structure they were designed to protect. While steel studs were utilized in the panelized structure, feasible curtain-wall designs were also developed and prototyped for wood-framing, CLT, and precast concrete as part of the project.
Looking ahead, there will continue to be innovation in design and construction of fast and durable facades for taller wood buildings. New prefabricated panel designs incorporating CLT panels and connection technologies from unitized curtainwall systems are already being developed for the “next tallest” wood buildings in North America.
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.
Mass timber and CLT construction offers many advantages, such as enhanced modularity, reduced construction schedules, improved thermal performance, and material sustainability. However, mass timber’s propensity to absorb moisture from the environment and the relative vapor impermeability of CLT panels introduces unique challenges when incorporated with the building enclosure. These challenges should be considered during design and construction phases to ensure long-term performance.
The VaproShield Mass Timber Building Enclosure Design Guideline covers the best practices for the design and construction of high-performance CLT wall and roof assemblies. RDH is the principal author and editor of the guide and within its capacity, we do not purport to endorse any specific material or technical matter within this guide.
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.
Project contact is Pierre Blanchet at Université Laval
The work of Lessard et al. (2017) demonstrated that the building envelope was an important system in the building in terms of environmental impact, but only took into account the external components of the building envelope. This project will perform a life cycle analysis of the main building envelopes for a typical building under commercial construction. By relying on our design partners, the main systems and associated materials will be analyzed in a cradle-to-grave approach. It is desirable to identify hot spots and to indicate avenues for product development in order to reduce the envelope's environmental footprint. Among the scenarios to be considered: light framework, CLT, curtain walls and all their possible variants, but also commonly used non-biobased systems. The comparison between the systems studied will be based on an equivalent energy efficiency performance.
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.