Toronto Mass Timber Construction

Mass timber buildings have experienced a spike in popularity among designers and developers in Toronto. As of August 2020, there are over 20 mass timber buildings at various stages of development in Toronto and Greater Toronto Area. The projects are using the gamut of mass timber materials such as CLT, DLT, NLT, and Glulam. Of particular note has been an increase in interest in mass timber residential buildings.

Of particular note is the 77 Wade Avenue project, close to Bloor Street and Lansdowne on the west side of Toronto and the T3 Bayside project at the Waterfront, not far from downtown Toronto. Both projects are following the alternative solution process to allow for a mass timber building above six storeys.

Proposed changes to the 2020 edition of the National Building Code of Canada (NBCC) will permit mass timber construction of up to 12 storeys. This will help to simplify building permit approvals and cement the widespread use of mass timber as a building system.

What is allowed under the current regulation?

Under the NBCC and the Ontario Building Code (OBC), timber construction is permitted for the major occupancy classification types summarized in the tables below.

Table 1 – Combustible construction under the Ontario Building Code (OBC) 2012 amended to date\

With the exception of the newly introduced Group C retirement home classification in the OBC, the provisions in the Ontario Building Code are very similar to those in the National Building Code.

Table 2 – Combustible construction under the National Building Code of Canada 2015

Key challenges under the current regulation

In recent years, the Canadian building industry has seen a marked increase in tall timber projects. This has breached the bounds of both the OBC and the NBCC’s prescriptive requirements, and resulted in proposals to build mass timber residential and office towers beyond six storeys.

Proposed NBCC changes – encapsulated mass timber construction

The proposed changes to the 2020 NBCC are approved in principle and will introduce a new construction requirement for Group C and Group D major occupancy classifications (under NBCC 3.2.2.48 and NBCC 3.2.2.56). Encapsulated mass timber construction will be a third construction type, in addition to the already existing combustible and non-combustible construction types.

Under this new construction type, mass timber construction will be permitted for Group C and Group D major occupancies up to 12 storeys high. However, the NBCC acceptable solution will require encapsulation of a significant portion of the surfaces of the mass timber ceilings, walls, beams, and columns.

Note, however, that encapsulated mass timber construction is not combustible construction! These are two distinct terms in the proposed NBCC 2020. The revised definitions of the three construction types are as follows:

• Combustible construction means that type of construction that does not meet the requirements for noncombustible construction or encapsulated mass timber construction.
•  Noncombustible construction means that type of construction in which a degree of fire safety is attained by the use of noncombustible materials for structural members and other building assemblies.
•  Encapsulated mass timber construction means that type of construction in which a degree of fire safety is attained by the use of encapsulated mass timber elements with an encapsulation rating and minimum depth and cross-sectional dimensions for structural members and other building assemblies.
•  Encapsulation rating means the time in minutes that a material or assemblage of materials will delay the ignition and combustion of encapsulated mass timber elements when it is exposed to fire under specified conditions of test and performance criteria, or as otherwise prescribed by this Code.

Encapsulated mass timber construction is simply mass timber construction with an encapsulation rating. This rating ought not be confused with the building’s fire resistance rating, as the encapsulation rating only delays the time to ignition and combustion of the protected mass timber elements. Encapsulation of the mass timber elements may be provided by type X gypsum board, gypsum concrete topping or any noncombustible material with an encapsulation rating of no less than 50 minutes.

In short, encapsulated mass timber construction will meet the Code’s general provisions for noncombustible construction. That said, provisions and permissions for combustible construction will not apply to encapsulated mass timber construction.

Under this new construction type, the fraction of exposed surfaces of mass timber elements permitted within a suite or fire compartment are as follows:

• The exposed surfaces of mass timber beams, columns and arches will represent no more than 10% of the total wall area of the perimeter of the suite or fire compartment. Similarly, the flame spread rating of the exposed surface will be no higher than 150.
• Provided each exposed surface faces the same direction, the exposed surfaces of mass timber walls within a suite need not be protected. The flame spread rating of the exposed surface will be no higher than 150.
• The aggregate exposed surface area of mass timber beams, columns, arches and walls within a suite will account for less than 35% of the total wall area of the suite perimeter.
• Any mass timber ceilings exposed within a suite will represent:
  • No more than 10% of the total ceiling area of the suite, with a flame spread rating of no more than 150, OR

Future of Mass Timber

The proposed changes to the NBCC have set the stage for the greater use of mass timber in Toronto and Canada. The challenge now becomes delivering a mass timber residential building that is in line with the current cost of construction of a concrete or steel building.

Photo credit for: 80 Atlantic Avenue, Toronto