Canadian Consulting Engineer

Feature

Protecting the Exterior

Following the tragedy of the Grenfell Tower fire in London, where flames consumed the building's exterior, could the same happen here?


Upper Grenfell Tower

When a building fire occurs that claims lives, the tragedy is followed by a period of reflection where we wonder if it could happen again elsewhere.

It is certainly ill conceived to draw conclusions about what really happened without all the evidence, and it can be outright dangerous to do so. However, when those conclusions are reached through a proper course of study, we try to learn from it and take the opportunity to revise regulations to help better protect society where possible.

This article focuses in on one aspect of building fire safety that is being looked at as a result of the fire in the Grenfell Tower in London, UK. That aspect is fire growth on the exterior of a building.

An exterior building fire is probably the fastest way to spread fire through a building because there are no fire barriers to stop it once it starts, there are no compartments to contain it, it could be aided by wind, and the vertical nature of the fuel arrangement feeding the fire.

That is not to say that such a fire is necessarily larger, or that it releases more heat or even that it is more dangerous than any other building fire, just that it typically moves faster than other building fires. In order for such a fire to propagate up the side of a building, combustible material must be in place with flame spread properties that would allow it to happen along with other factors.

The building code system in Canada regulates the combustible content of construction materials including exterior cladding. Buildings over six stories high must be constructed with material determined to be noncombustible including the exterior cladding. Some relaxation of this requirement is provided for smaller buildings required to be of noncombustible construction, however those buildings require non-loadbearing walls to meet vertical flame spread criteria.

That covers newly constructed buildings, but what about buildings that have been around for a while that get renovated? Renovations are covered by provincial building codes that include provisions related to exterior cladding. Any project that includes replacing or adding to the exterior wall assembly of a building is subject to the requirements of the building code in the jurisdiction of the proposed project. In addition to the provisions of the building code, every occupied building is covered by the fire code that prohibits changes that would make a building less safe than originally designed without meeting the requirements of the building code.

 

History of Code Provisions related to exterior cladding

In the 1980 National Building Code of Canada the use of foamed plastics began to receive specific attention. Starting with the 1990 version, combustible cladding for buildings required to be of noncombustible construction has been addressed in a separate article. From this we can see that for over 30 years the use of plastics in exterior building cladding has been included in Canadian Building Code regulations. The cladding on the Grenfell Tower included a polyethylene (thermoplastic) core.

 

Could the same thing
happen here?

When comparing what is known about the fire at Grenfell Tower with the residential building inventory in Canada, the question “could that happen here?” comes up. Despite all of the protection measures put in place to limit the probability of such an occurrence, unfortunately, the answer is yes.

All it would take is the inattention, or lack of understanding of this potential risk, by a small group of key people involved with an exterior cladding renovation project to create similar conditions to those which ultimately turned a single unit apartment fire into one like we witnessed in London.

The consequences of such a fire in terms of lives lost and property damage caused is another matter altogether and will likely be the subject of many studies conducted in the near future.

If a similar event were to occur in this country, the ultimate responsibility would be with the building owner who is responsible to ensure that renovations meet the requirements of the building and fire codes, but there would be plenty of blame to go around.

Product manufacturers should ensure their products are tested by accredited labs and listed as being non-combustible, or that they achieve flame spread criteria minimums before they are marketed to buildings in general. Architects, engineers, designers and installers should ensure that the proper application of materials is achieved and that construction permits are issued to achieve the requirements of Canadian building and fire code regulations with the assistance of building officials.

 

Cladding systems

There is no doubt that buildings operate more efficiently when they are insulated from the exterior environment, and one of the easiest ways to improve that efficiency on an existing building is through the addition of exterior insulated cladding.

Such cladding can also improve the look of an older building. For these reasons an increasing number of products and projects will seek to add exterior insulated cladding materials to buildings, but we must remain true to the objectives of our construction codes in order to ensure that safety is not sacrificed to achieve other goals.

The cladding used in the Grenfell Tower has been reported to be Reynobond PE, an architectural product intended to be part of a vented cladding system used for new construction or renovation.

Manufactured by Arconic, formerly part of Alcoa, the Reynobond product consists of two aluminum sheets bonded to a thermoplastic (polyethylene) core. The products are available as Reynobond PE, with the polyethylene core and Reynobond FR, which is fire-resistant and includes a polyethylene core loaded with mineral flame retardant.

A product sheet from a building supplier’s website indicates that Reynobond is listed to ASTM E 84 (for use in the United States).

A search of the ULC database for that product shows it is not listed for use as either a noncombustible or an acceptable vertical flame propagation resistant material. The FR version of the product is listed by UL as part of several building exterior wall assemblies, but no listing for the PE product was found.

What this means is the material is not acceptable for use in any exterior cladding project in Canada for buildings over three storeys in height.

If all that sounds a bit confusing, that is because it can be and often is. So it’s no stretch of the imagination to see how a bit of inattention on the part of some key players could affect public safety.

William Kuffner, P.Eng. is Senior Fire Protection Engineer, Infrastructure Engineering with SNC-Lavalin.