Wooden Housing Constructions: Evolution of Practices

//Wooden Housing Constructions: Evolution of Practices

Wooden Housing Constructions: Evolution of Practices

Context Elements

The National Building Code of Canada (hereinafter NBC) has allowed, since its first publication in 1941, that buildings be of combustible construction (including wood) together with structural and non-structural elements. At that time, large timber buildings could have four (4) storeys while those with lightweight framing were limited to three (3) storeys. The presence of sprinklers only had a limited influence on the permitted building area.

Even today, the choice by professionals to design combustible construction buildings must be made according to the specific conditions and requirements mentioned in the NBC, more specifically in subsection 3.2.2. The Régie du Bâtiment du Québec (RBQ) was innovative in its approach to combustible construction when it adopted the NBC 2010 amended version in June 2015.

Indeed, the “original version ” of the NBC 2010 QC, as published by the National Research Council of Canada (NRC), always limited combustible construction to no more than four (4) floors even if sprinklered. The RBQ, following the publication of its guide “Construction of 5 or 6-storey WOODEN DWELLINGS” in 2013 introduced requirements that allowed the construction of 5 and 6-storey combustible residential and business buildings. This lightweight wood framing was permitted under strict conditions, including sprinkler protection, a maximum height of 18 m on the top floor and a maximum building area of 1,500 m2 when used as a residential building. It should be noted that the 2015 version of the NBC 2010 QC, as published by the NRC (still not adopted by Quebec), allows this type of 5 and 6 storey construction (some requirements/conditions are different from the Quebec version).

Figure 1. Guide for the construction of 5 or 6 floors residential buildings
(source: RBQ)

New Materials, New Regulations

In parallel with this progress in lightweight frames, a new type of construction with “solid” wooden frames has appeared on the market: glued laminated timber but mostly CLT (cross-laminated timber). The latter type of material from Scandinavian countries arrived on the North American market in the early 2010s. The limit of six (6) storeys (light frame) can therefore be extended, from a structural point of view, to more than thirty (30) storeys! But the scientific community, the authorities with jurisdiction and the fire services are wondering: is it safe if a fire breaks out in such buildings?

Figure 2. Cross-laminated timber (source: FPInnovationS)

Research institutes around the world, including NRC, as well as groups representing the wood industry are therefore working to advance research in this area. Laboratory tests (small and large scale) are carried out in Europe, North America and Australia.

Figure 3. Tests in a furnished room with exposed BLC walls (source: A. R. Mediva Hevia)

Not being a type of construction recognized by the Quebec version of the NBC 2010, it was necessary to present an equivalent measure to the RBQ to have the construction of a building with more than six (6) floors accepted. The “Origine” residential condominium project in Quebec City was presented to the RBQ in the fall of 2014 and was accepted in the spring of 2015. This twelve-storey building, made in BLC and resting on a reinforced concrete podium on the ground floor
(13 floors in total), was completed at the end of 2017.

Figure 4. “Origin” project (source: Google Maps)

Furthermore, in the summer of 2015, the RBQ published a new guide to this type of construction, “Massive wooden buildings of no more than 12 storeys in height instructions and explanatory guide”. From then on, residential and business buildings are allowed to be built with a solid wood structure that is encapsulated in gypsum. Unfortunately for designers, wood surfaces cannot be visible with this guide, which is intended as a pre approved equivalent measure of NBC 2010 QC.

Figure 5. Guide for a 12 storey solid wood construction (source: RBQ)

What About Now ?

Where do we stand today? Scientific research continued to demonstrate in recent years that it is possible to have a certain amount of solid wood exposed in rooms and areas. NRC will publish the next version of the NBC (2020) by fall 2020, which will allow the construction of solid wood encased in gypsum, allowing exposed visible wall surfaces, ceiling or structural elements (columns and beams) only under certain conditions. For now, it is necessary to introduce an equivalent measure for the RBQ to allow visible surfaces. However, it is likely that the RBQ if the past is the guarantee for the future will either adopt these new provisions quickly enough (for exposed wood) either in the future version of its code or via a guide as it has done in the past.

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By Marc-André Langevin, President

By |2019-09-19T16:42:33+00:00September 19th, 2019|News|0 Comments