Cross-laminated timber has been used in buildings since the 1990s. In the last years, there has been a growing interest in the use of this technology, especially with the adoption of the product in increasingly taller buildings. Considering that the product is manufactured from a combustible material, wood, authorities that regulate the fire safety in buildings and the scientific community have carried out numerous research and fire tests, aiming to elaborate codes which contemplate the use of cross-laminated timber in tall buildings. This paper discusses the main results obtained from the fire resistance test of a cross-laminated timber slab carried out in the horizontal gas furnace (3.0 m × 4.0 m x 1.5 m) from the University of Sao Paulo. A vertical load of 3 kN/m2 was applied over the slab and the specimens were exposed to the standard fire curve for 30 min. In addition to the 30-min test, the research also evaluated the thermal behavior of the samples during the 24 h after the burners were turned off. Throughout the test, the slab maintained the integrity and the thermal insulation, and no falling-off of the charred layer was observed. However, the 24-h test indicated that it is mandatory to consider the loss of stiffness and strength of timber caused by the thermal wave observed during the decay phase.
The building industry consumes a lot of material, which causes depletion of material stocks, toxic emissions, and waste. Circular building design can help to reduce this impact, by moving from a linear to a circular design approach.
To reach a circular build environment, all disciplines should be involved, including fire safety design. However, there is a contradiction between the objectives of circular and fire safety design, either affecting the aim of protection of material sources, or protection against fire risk.
Timber is a material that has high potential in contributing to a circular building industry, as it is renewable, recyclable and can store CO2. However, timber is combustible, which increases the risk of fire. Therefore, mass timber building design has traditionally been restricted by building regulations. To enhance mass timber building design research on timber buildings has increased, to allow understanding of the risks. However, yet general guidelines or understanding on the fire behaviour and risk in timber buildings is lacking. This is a problem for the fire safety design and the potentials of timber contributing to a circular building industry.
Until now, there was no specific method available that quantifies this relation between material use and fire risk in mass timber buildings. This limits the possibility of fire safety design and mass timber design to contribute to a more circular building industry. By creating a method that allows comparison between the economic and environmental impact of material use and fire risk, a well-founded choice of building materials is easier to make.
The design tool created in this research quantifies the impact on material use for fire safety measures relating to CLT, encapsulation and sprinkler availability and their effect on the fire risk in mass timber buildings. This way insight is provided between the balance of material use and fire risk. By the sum of the impact on material use and fire risk, the total “circular fire safety impact” value is calculated. This value represents the total economic and environmental impact of the design based on the choice of building materials. By changing the fire safety design, the most optimal design variant can be determined. This is the variant with the lowest total impact value.
This way, a circular design approach is used to steer fire safety design in mass timber buildings towards a design solution that does not only provide sufficient safety for people, but also provides maximum economic and environmental safety from a material point of view.
Many real-scale fire tests have been performed on timber connections to analyze the mechanical behavior of timber connections in previous years. However, little research focused on the bending performance of glued laminated (glulam) timber beam bolted connections after fire exposure. In this paper, the three-dimensional numerical model of the glulam timber beam bolted connections was developed and validated by experimental results. The model can simulate temperature evolution in the connections and their mechanical behavior. In the real-scale test, three (3) samples were prepared for a four-point bending test at normal temperature, while another three (3) samples were tested after exposure to a 30-min standard fire and cooled down to normal temperature. The results show the reduction of the load-carrying capacity before and after exposure to the standard fire by 23.9 kN (71.8%), 8.3 kN (26.1%), and 20.2 kN (47.6%) for bolt diameters of 12 mm, 16 mm, and 20 mm, respectively. The numerical model aims to conduct a parametric study and propose the modification of the exponential decay constant, k, for tropical glulam timber to predict the load-carrying capacity of the glulam timber beam bolted connections after exposure to standard fire.
The goal of this research was to develop a simple laboratory test for examining heat delamination in cross-laminated timber (CLT) panels. The laboratory test was designed to mimic the fire tests described in Annex B of the ANSI/APA PRG-320 standard, which is required for CLT product qualification in North America. The Annex B test requires a full-sized room (2.4 by 4.9 by 2.7 m) to be constructed and exposed to a design fire scenario. In this article, we scaled the mechanical and fire loads so that they could be conducted in an intermediate-scale furnace with 1.1 m2 of exposed CLT panels. The mechanical loads were scaled to match the bending moment prescribed in the standard. The fire loads were scaled by matching the temperature profiles when an inert furnace lid was run and then matching the gas flow on all subsequent tests. Panels made from adhesives that passed the Annex B test passed the laboratory-scale test; panels that failed the Annex B test failed the laboratory test with the exception of one replicate. Correlations were found not only for CLT but also for a veneer-based mass timber panel. Measured temperature profiles within the furnace were similar to those measured near the compartment ceiling in the Annex B test. The scaled-down test in this article can be used to screen which adhesives are likely to pass the full-scale Annex B test.
Fire safety remains a major challenge for engineered timber buildings. Their combustible nature challenges the design principles of compartmentation and structural integrity beyond burnout, which are inherent to the fire resistance framework. Therefore, self-extinction is critical for the fire-safe design of timber buildings.
This paper is the first of a three-part series that seeks to establish the fundamental principles underpinning a design framework for self-extinction of engineered timber. The paper comprises: a literature review introducing the body of work developed at material and compartment scales; and the design of a large-scale testing methodology which isolates the fundamental phenomena to enable the development and validation of the required design framework.
Research at the material scale has consolidated engineering principles to quantify self-extinction using external heat flux as a surrogate of the critical mass loss rate, and mass transfer or Damköhler numbers. At the compartment scale, further interdependent, complex phenomena influencing self-extinction occurrence have been demonstrated. Time-dependent phenomena include encapsulation failure, fall-off of charred lamellae and the burning of the movable fuel load, while thermal feedback is time-independent. The design of the testing methodology is described in reference to these fundamental phenomena.
This paper provides understanding of the fire performance of exposed cross-laminated-timber (CLT) in large enclosures. An office-type configuration has been represented by a 3.75 by 7.6 by 2.4 m high enclosure constructed of non-combustible blockwork walls, with a large opening on one long face. Three experiments are described in which propane-fuelled burners created a line fire that impinged on different ceiling types. The first experiment had a non-combustible ceiling lining in which the burners were set to provide flames that extended approximately halfway along the underside of the ceiling. Two further experiments used exposed 160 mm thick (40-20-40-20-40 mm) loaded CLT panels with a standard polyurethane adhesive between lamella in one experiment and a modified polyurethane adhesive in the other. Measurements included radiative heat flux to the ceiling and the floor, temperatures within the depth of the CLT and the mass loss of the panels. Results show the initial peak rate of heat release with the exposed CLT was up to three times greater when compared with the non-combustible lining. As char formed, this stabilised at approximately one and a half times that of the non-combustible lining. Premature char fall-off (due to bond-line failure) was observed close to the burners in the CLT using standard polyurethane adhesive. However, both exposed CLT ceiling experiments underwent auto-extinction of flaming combustion once the burners were switched off.
Fire safety greatly contributes to feeling safe, and it is a key parameter for the selection of building materials. The combustibility of timber is one of the main reasons to have the strict restriction on timber for use as a building material, especially for multistory buildings. Therefore, the main prerequisite for the use of timber in buildings is to ensure adequate fire resistance, using passive and active fire protection measures. This article contains the results of mechanical and fire experimental tests of both normal and innovative hollow glued laminated timber beams. A total of 10 timber beams were tested at ambient temperature, and 3 timber beams in fire conditions, which differed in cross-section type but also in the applied fire protection. The first beam was a normal GL beam without fire protection, the second a hollow beam covered by intumescent paint, while the third was also hollow, additionally protected by mineral wool infill inside the holes. The load-carrying capacity of the hollow beam in ambient conditions was estimated at 65% of the load-carrying capacity of a normal GL beam. Fire tests indicated that hollow timber beams with both intumescent paint and mineral wool infill failed at a similar time as a normal GL beam without fire protection. One-dimensional ß0 and notional charring rates ßn were obtained. Time to the protective material failure was 17 min. The main cause of failure of hollow beams was the appearance of delamination due to the reduction of the lamella bonding surface.
This paper models bench-scale experiments using computational fluid dynamics (CFD). The experiments measured the temperature profiles of fire-protected cross laminated timber (CLT) specimens exposed to parametric fire curve. The bench-scale experiment specimen is 250 x 250 mm and consists of a CLT panel 100 mm with three layers of gypsum plasterboard 15.5 mm as thermal and fire insulation. The specimens were exposed to a heat flux generated by a heat-transfer rate inducing system (H-TRIS) device. Two numerical models were created in order to copy the experiment conditions, one by using basic modelling techniques and one using advanced method. Comparing the layer temperature values of the experiment and basic model, a great difference was found. The difference between experimental and model temperatures increases the closer the analysed layer is to the heat source. The results show a good agreement between the model and the experiments, especially for the advanced numerical model.
The use of mass timber in buildings instead of non-combustible materials has benefits in sustainability, aesthetics, construction times, and costs. However, the uptake of mass timber in modern construction for medium and high-rise buildings is currently hindered by uncertainty regarding safety and structural performance in fire. We attribute this to a lack of data. Insufficient understanding means that for building designs beyond the current range of experiments the fire performance is unknown. To address this uncertainty, we review the available data in the scientific literature from 63 compartment fire experiments with timber, the majority of which use cross-laminated timber (CLT). We found that most experiments reached temperatures 80–180°C greater than in non-combustible compartments. Timber ceilings have on average a 16% lower char rate than timber walls. The heat release rate contribution of timber has a positive linear relationship with charring rate, however is susceptible to significant uncertainty and variability. There are limits to the data available, particularly in large open-plan compartments of floor areas larger than 100 m2 where a wider range of heating conditions occur. Other topics where further understanding is required are compartments with exposed timber areas greater than 75%, compartments with smaller opening areas, and the hazard of smouldering following the flames. Therefore, additional research is needed to design beyond the limits, specifically in compartment size, ventilation, and timber exposure. This paper identifies correlations in the current body of experimental research to improve fire-safe design of timber buildings.
Concealed spaces, such as those created by a dropped ceiling in a floor/ceiling assembly or by a stud wall assembly, have unique requirements in the International Building Code (IBC) to address the potential of fire spread in nonvisible areas of a building. Section 718 of the 2018 IBC includes prescriptive requirements for protection and/or compartmentalization of concealed spaces through the use of draft stopping, fire blocking, sprinklers and other means.
Changes to the 2021 International Building Code (IBC) have created opportunities for wood buildings that are much larger and taller than prescriptively allowed in past versions of the code. Occupant safety, and the need to ensure fire performance in particular, was a fundamental consideration as the changes were developed and approved. The result is three new construction types—Type IV-A, IV-B and IV-C—which are based on the previous Heavy Timber construction type (renamed Type IV-HT), but with additional fire protection requirements.
One of the main ways to demonstrate that a building will meet the required level of passive fire protection, regardless of structural materials, is through hourly fire-resistance ratings (FRRs) of its elements and assemblies. The IBC defines an FRR as the period of time a building element, component or assembly maintains the ability to confine a fire, continues to perform a given structural function, or both, as determined by the tests, or the methods based on tests, prescribed in Section 703.
FRRs for the new construction types are similar to those required for Type I construction, which is primarily steel and concrete. They are found in IBC Table 601, which includes FRR requirements for all construction types and building elements; however, other code sections should be checked for overriding provisions (e.g., occupancy separation, shaft enclosures, etc.) that may alter the requirement.
The fire resistance of a structural building member includes its ability to survive a specified fire without loss of its loadbearing function. For glue laminated timber columns, fire resistance is determined by either subjecting a structural member to a standard fire test or by using one of two accepted calculation methods. For wood structural members, the calculation methods rely on char rates obtained from numerous standard fire tests. The existing calculation methods are limited under United States building codes to calculating fire resistance ratings of 120 minutes or less. However, over the past decade there has been a push towards tall wood buildings and designers desire more exposed wood to be permitted in buildings. This desire, coupled with the recent adoption of code language that permits tall wood buildings up to 18 stories, has resulted in the need to determine char rates for glue laminated timber to use in the fire resistance calculations up to 180 minutes. Here we present the experimental method and initial char rate results of glue laminated columns exposed to the standard fire.
One component PUR adhesive is widely used in engineered wood products applications, such as cross-laminated timber (CLT). However, the dramatic deterioration of PUR adhesive bond strength at elevated temperature can out tremendously threat for tall wood building, especially under fire. In this project, we are aiming to improving the bond strength of the PUR adhesive at high temperature by incorporating chemically modified halloysite to improve the poor interface between inorganic fillers and the polymer matrices. To improve the interaction with PUR (Loctite UR20 by Henkel®), the halloysite was chemically grafted with polymeric diphenylmethane diisocyanate (pMDI) (pMDI-H). The effect of adding pMDI modified halloysite to the PUR adhesives was investigated in terms of nanofiller dispersibility, thermal and mechanical properties of the pMDI-halloysite-PUR composite film, and the bonding shear strength of the glued Douglas fir and Spruce-Pine-Fir (SPF) shear blocks under different temperature.
Significant improvement of the bond shear strength can be observed with the addition of 5 and 10% of pMDI-modified PUR adhesive, and the key research findings are summarized as below,
a. pMDI can be successfully grafted onto hydroxylated halloysites to improve its dispersibility in one-component PUR adhesive;
b. Addition of pMDI-H into PUR adhesive can lead to improved glass transition temperature and storage modulus. In contrast, no significant enhancement was observed in h-H added PUR films due to the poor dispersibility;
c. Addition of up to 10% h-H and pMDI-H did not show significant change of the shear strength at 20 °C for both Douglas Fir and SPF;
d. Significant enhancement of shear strength at elevated temperature (60-100 °C) can be observed for 5% and 10% pMDI-H modified PUR adhesive, showing 17% improvement for Douglas Fir and 27-37% for SPF.
The results of an experimental programme on the structural behaviour, fire behaviour, and fire resistance of CLT rib panels are presented. The floor system consists of cross-laminated timber (CLT) plates rigidly bonded to glued-laminated timber ribs by means of screw-press gluing.
The experimental programme comprised ultimate-load tests at normal temperature as reference tests and full-scale fire resistance tests on four cross-sections. In addition to the reference tests, shear tests of the glue line between CLT plate and glued-laminated timber rib were performed for analysis of the cross-sections’ composite action.
The results of the reference tests show good agreement with results based on the simplified method according to EN 1995-1-1  and its final draft of CLT design . The importance of the glue line’s quality was confirmed. The fire resistance tests show results on the safe side compared to predictions of the fire behaviour according to EN 1995-1-2  and its actual draft . However, the fire resistance was underestimated due to conservative assumptions about the composite cross-section’s structural behaviour.
The experimental programme addressed the fire behaviour and fire resistance of CLT rib panels currently not covered in standards. The project’s overall aim is the development of design rules in fire for EN 1995-1-2.
This InfoNote summarizes recent research and work in progress. A significant amount of fire research has been conducted on mass timber over the last 10 years in Canada. This has supported the successful design and construction of numerous low-, mid-and even high-rise wood buildings. This has also fostered the introduction of new provisions into the National Building Code of Canada which has made wood and mass timber construction more accessible. However, the fire performance of these systems remains a concern for many potential occupants or owners of these buildings, not to mention building officials and fire departments. Research at FPInnovations continues to support designers and builders in the use of mass timber assemblies by ensuring fire safe designs.
Building elements are required to provide sufficient fire resistance based on requirements set forth in the National Building Code of Canada (NBCC). Annex B of the Canadian standard for wood engineering design (CSA O86-19) provides a design methodology to calculate the structural fire-resistance of large cross-section timber elements. However, it lacks at providing design provisions for connections. The objectives of this study are to understand the fire performance of modern mass timber fasteners such as self-tapping screws, namely to evaluate their thermo-mechanical behavior and to predict their structural fire-resistance for standard fire exposure up to two hours, as would be required for tall buildings in Canada. The results present the great fire performance of using self-tapping screws under a long time exposure on connections in mass timber construction. The smaller heated area of the exposed surface has limited thermal conduction along the fastener’s shanks and maintained their temperature profiles relatively low for two hours of exposure. Based on the heat-affected area, the study presents new design principles to determine the residual length of penetration that would provide adequate load-capacity of the fastener under fire conditions. It also allows determining safe fire-resistance values for unprotected fasteners in mass timber construction exposed up to two hours of standard fire exposure.
This paper is intended for developers and owners seeking to purchase insurance for mass timber buildings, for design/construction teams looking to make their designs and installation processes more insurable, and for insurance industry professionals looking to alleviate their concerns about safety and performance.
For developers, owners and design/construction teams, it provides an overview of the insurance industry, including its history, what affects premiums, how risks are analyzed, and how project teams can navigate coverage for mass timber buildings. Insurance in general can seem like a mystery—what determines premium fluctuations, impacts of a strong vs. weak economy, and the varying roles of brokers, agents and underwriters. This paper will explain all of those aspects, focusing on the unique considerations of mass timber projects and steps that can be taken to make these buildings more insurable.
For insurance brokers, underwriters and others in the industry, this paper provides an introduction to mass timber, including its growing use, code recognition and common project typologies. It also covers available information on fire performance and post-fire remediation, moisture impacts on building longevity, and items to watch for when reviewing specific projects.
When a new engineered wood adhesive is developed for use in a fire-rated assembly, it must first pass a full-scale fire test, for example, a test in accordance with ASTM E119 in the United States. Although full-scale tests serve as the necessary entry to the marketplace, they are extremely costly and reflect the performance of the entire assembly and not just the adhesive. As a result, it is difficult to quantify differences in adhesive performance under elevated temperatures or fire conditions with these tests. Here, we present the results from a new test method developed at the USDA Forest Service, Forest Products Laboratory, to examine adhesive wood performance in glulam beams. The test is part of a larger research program for examining different adhesive formulations. The goals of the intermediate-scale test were to understand differences between adhesive formulations and to provide guidance regarding the performance for full-scale adhesive tests.
The development of this primer commenced shortly after the 2018 launch of the Mass Timber Institute (MTI) centered at the University of Toronto. Funding for this publication was generously provided by the Ontario Ministry of Natural Resources and Forestry. Although numerous jurisdictions have established design guides for tall mass timber buildings, architects and engineers often do not have access to the specialized building science knowledge required to deliver well performing mass timber buildings. MTI worked collaboratively with industry, design professionals, academia, researchers and code experts to develop the scope and content of this mass timber building science primer. Although provincially funded, the broader Canadian context underlying this publication was viewed as the most appropriate means of advancing Ontario’s nascent mass timber building industry. This publication also extends beyond Canada and is based on universally applicable principles of building science and how these principles may be used anywhere in all aspects of mass timber building technology. Specifically, these guidelines were developed to guide stakeholders in selecting and implementing appropriate building science practices and protocols to ensure the acceptable life cycle performance of mass timber buildings. It is essential that each representative stakeholder, developer/owner, architect/engineer, supplier, constructor, wood erector, building official, insurer, and facility manager, understand these principles and how to apply them during the design, procurement, construction and in-service phases before embarking on a mass timber building project.
When mass timber building technology has enjoyed the same degree of penetration as steel and concrete, this primer will be long outdated and its constituent concepts will have been baked into the training and education of design professionals and all those who fabricate, construct, maintain and manage mass timber buildings.
One of the most important reasons this publication was developed was to identify gaps in building science knowledge related to mass timber buildings and hopefully to address these gaps with appropriate research, development and demonstration programs. The mass timber building industry in Canada is still a collection of seedlings that continue to grow and as such they deserve the stewardship of the best available building science knowledge to sustain them until such time as they become a forest that can fend for itself.
This manual is helpful for experts and novices alike. Whether you’re new to mass timber or an early adopter you’ll benefit from its comprehensive summary of the most up to date resources on topics from mass timber products and applications to tall wood construction and sustainability.
The manual’s content includes WoodWorks technical papers, Think Wood continuing education articles, case studies, expert Q&As, technical guides and other helpful tools. Click through to view each individual resource or download the master resource folder for all files in one handy location. For your convenience, this book will be updated annually as mass timber product development and the market are quickly evolving.