About Vinyl Cladding and soffits

The use of vinyl siding as cladding and soffit material is very widespread in Whitehorse.  It’s low cost, low maintenance and wide colour range have been strong selling points.  However, research with the insurance industry in Canada and leading authorities in the United States strongly discourages its use in wildfire prone areas like Whitehorse.

Some important details:

• Vinyl siding melts when exposed to even low intensity radiation from a nearby fire.  It’s melting temperature is only 80-100°C (boiling water) and it liquifies at 250°C (temperature of a hot oven).

• Vinyl soffits will similarly melt under low intensity radiation but, in this case, they will expose the roof structure to ember entry and fire propagation.

• Melted vinyl will catch fire at 500°C producing very toxic fumes (hydrochloric acid).

Comparison of Fire Resistance of Vinyl Siding vs Cedar Wood Siding

New building codes for housing in wildfire-prone areas prohibit the use of vinyl siding or soffits, requiring non-combustible materials in both applications.

Proposed zoning bylaw changes in Whitehorse encourage the construction of multiple dwelling units on single properties.  This will reduce the distance between buildings thereby increasing the risk of fire spread.  Given the vulnerability of vinyl cladded structures, at minimum new structures less than, say, 15 ft apart should have non-combustible siding and soffits on the facing walls.

Refences

1.       Moisture, Impact, Fire and Pest-Resistant Exterior Siding – Building America Solution Centre

2.       Wildland Urban Fire Resilient Housing – a presentation by LEEP, NRC Canada, July 2024 – copy available.

3.       Jack Cohen, personal communication – June 6, 2025