September 12th 2025

Intel

Vegetated Roofs

Green or vegetated roofs have gained interest in recent years and have been proposed for several projects we have supported. However, this type of overburden (material overlaying the roof structure) is not contemplated by the National Building Code of Canada or the BC Building Code. This creates challenges with Part 3 buildings where the Building Code restricts roof covering materials to minimize the risk of fire spread across roofs. Roof coverings of Part 3 buildings are generally required to be classified in accordance with CAN/ULC-S107 as Class A, B, or C, or meet one of the provided exceptions which are generally limited to noncombustible materials. Plant material, particularly when not maintained and allowed to dry out, can become a fire spread hazard.

The 2019 Vancouver Building By-Law implemented requirements for the design of vegetated roofs to facilitate the inclusion of these overburdens into buildings within the City. These provisions have been carried into the 2025 Vancouver Building By-Law that comes into force on September 15, 2025, next week. The by-law provides a definition for vegetated roof assemblies and requires the assemblies be designed and constructed in conformance with ANSI/SPRI VF-1 "External Fire Design Standard for Vegetative Roofs".

Outside of the City of Vancouver, Part 3 building designs incorporating a vegetated roof where the roof covering material is restricted by Article 3.1.15.2., should be implemented with the use of an Alternative Solution.

If you have a building design where it is proposed to implement a vegetated roof and it is located outside the City of Vancouver, we would be pleased to support your project.

Green Wall Systems

While less popular than vegetated roofs, green wall systems are becoming more common. However, as with vegetated roofs, the National Building Code of Canada and the BC Building Code do not contemplate cladding systems composed of vegetation. In small buildings, cladding requirements can be unrestricted if limiting distances are adequate. However, in larger buildings required to be of noncombustible construction or buildings that are over 4-storeys in building height, cladding materials are restricted to control the spread of fire over the building face. In buildings with restricted cladding requirements, implementing a Green Wall system into the building cladding, will require an Alternative Solution.

This Article in Deezen discusses the available non-standard test procedures for green wall systems in the UK, where Architects may be under false impressions about the fire safety of these green wall systems.

Wisdom

Building Area

When analyzing a building for application of the National Building Code of Canada or the BC Building Code, "building area" is an important defined term in determining the construction requirements that are to be applied to the building. Larger building areas generally result in increased construction requirements for a building.

The building code defines building area as:

building area means the greatest horizontal area of a building above grade within the outside surface of exterior walls or within the outside surface of exterior walls and the centre line of firewalls.

I know when I read this, my initial thought was: what? If you have the same reaction, have no fear, you are not alone!

So what does this mean in practice, and what are good ways to think about what building area is?

A simple way to think of building area, though not accurate for all building designs, is that building area is the footprint area of the building. This works for buildings that are one storey and where all storeys are stacked and either the same size and shape, or the storeys above the ground level storey decrease in size. Think of a typical highrise on a podium - the building area will nearly always be the podium area.

A more accurate way to determine building area, that works for all buildings, is to take the outline of the exterior walls of every above grade storey, and superimpose these outlines onto the ground level - the building area is the largest area of the combined outlines.

"But Brian," you say, "What about where the building has a courtyard like in the image above or the design of the Barrington 1503 building in LA?" That is a great question and the details will determine if the central courtyard area can be excluded or not from the building area:

Where the courtyard is part of the 1st storey of the building, then the smallest area formed by the superimposing of all the above grade storey outlines for the courtyard, is excluded.
When the courtyard starts above the 1st storey, say on the roof of the 1st storey, then the storeys that form the courtyard no longer represent the greatest horizontal area, and the area of the courtyard is not excluded.
If there is a roof over the courtyard, it cannot be excluded from the building area as the walls of the courtyard are no longer "exterior walls".

Now, what if the building is a U shape and there is a canopy and not a roof over the courtyard. Do you know if the courtyard area can be excluded? This is where considerable judgment is required to be applied based on the specifics of the proposed design configuration. Unfortunately, whenever judgment is required there are often differences of opinion, which usually means between the Authority Having Jurisdiction and the Architect. When this happens, the interpretation of the building area definition can become challenging.

Do you have any stories or examples of building designs where building area was not a straightforward determination? I'd love to hear from you at bfraser@celerity.ca.

Tall Mass Timber

In the past the use of steel in mass timber buildings has generally been limited to connections between the timber elements. However, as mass timber construction becomes more mainstream as with the George Brown College building in Toronto, we are starting to see industry considering hybrid structures to meet the aesthetic vision of projects and to improve the economics for these structures.

The Canadian Wood Council in collaboration with the Canadian Institute of Steel Construction are working together to accelerate the adoption of steel-timber hybrid structural solutions in Canada through a new strategic partnership. I am excited to see these developments and the progress being made by industry to provide new construction material options for our buildings.

Intriguing

Gazebo Spatial Requirements

Gazebos and similar structures with only a roof and no exterior wall assemblies, can result in unexpected challenges when applying the building code. The usual issue we see, is with meeting the spatial separation requirements of the National Building Code of Canada or the BC Building Code.

The issue is that gazebos and similar structures typically have no physical exterior walls, so it is easy to assume that the spatial separation requirements of the building code do not apply. However, this is not how the guidance provided by the National Research Council of Canada views this situation. The guidance outlines that the exterior walls of these structures are to be taken at the drip line of the roof. This means that when there is no physical wall, the opening is considered to be a 100% unprotected opening for applying the spatial requirements and the limiting distance is the roof drip line. And, of course, 100% unprotected openings can demand large limiting distances.

For a gazebo or similar structure with no physical exterior walls, this seems a bit heavy handed given some of the assumptions used for basis of the spatial protection requirements in the building code are invalidated. The primary assumption of concern is that the fire is in a confined space that traps the hot fire gases, promoting elevated temperatures and the spread of fire throughout the compartment. However, in an open structure that has no exterior walls, hot fire gases will freely escape and the elevated temperatures seen in closed space testing, will not be reached. This results in a much lower risk of fire spread not just within the structure, but to adjacent buildings as well. Nevertheless, this is not recognized by the building code and we must apply the stringent spatial requirements to these structures.

In the image above and in this Dezeen Article on the Mitcham Fair Bandstand, the gazebo is located far from other structures, and therefore the spatial protection requirements allow for 100 % unprotected opens to permit no exterior walls. However, in most cases, it is desired by the owner to have these structures near other buildings or property lines to facilitate occupant use or due to available space. However, the spatial requirements of the building code must be met.

About

Ah, the kids are back to school. Such a great time of year!

If you found one of the Articles interesting, drop me a note at bfraser@celerity.ca. It is always great to hear everyone's thoughts on these topics!

Til next issue!