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Protect Your House from Wildfire With The Right Insulation

Thermal Insulation Doesn't Keep Your House Warm

A particular type of thermal insulation that is commonly used to prevent fire from passing from one part of a large building to another can prevent wildfires from burning down your house. Allow me to explain the material and how it provides this protection.

Right now, it seems as though the whole province is on fire. Firefighters continue to battle fires across the province (link) Actually, the whole country has been on fire since early June; wildfires literally from coast to coast have blanketed the entire continent with smoke. Many homes have been threatened, and we'll have to wait to see how many structures are destroyed by the time winter rolls around. The fires are now setting records for largest in history (link).

Only recently has exterior insulation - that which is installed between the outside of the plywood but still behind whatever siding material is used - become a requirement for wood-framed houses in many municipalities. Most of the houses that have some exterior insulation use a foam plastic board similar to Styrofoam. Whether your house has no exterior insulation or has foam plastic insulation, it is unlikely to stand up to flames attacking the wall.

Wildfires destroy many houses because of flying embers that land on the roofs. As well, many fires get into homes through windows that are not adequately protected. Doors are less vulnerable than windows but do provide additional opportunity for the fire. Vents into the house or into a crawlspace are another pernicious weakness. I will discuss a strategy to combat those challenges in a future article. In this article, I'm discussing protection of your exterior walls.

Insulation slows down the rate at which heat energy flows from one side to another. Because the Canadian climate is heating-dominated, insulation generally applies as preventing too much heat from leaving the interior of a building to the cold weather outside. We therefore generally file away in our heads the simplification of insulation as something that "keeps us warm", but it can also help prevent us or our buildings from getting too hot - hot enough that they're on fire. Once that happens, homes like this one are completely destroyed (video).


In large buildings, the building code has a requirement to prevent fire, smoke, and hot gases from passing from one part of the building to another. The walls, floors, and the joints where piping or ductwork pass from one part to another often include a material called mineral fibre insulation. Byproducts of steel production and other rock-like compounds are crushed and converted to fibres that are pressed together into firm yet slightly bendable boards or into fluffy blankets similar to fibreglass insulation.

A Danish-based international firm called Rockwool began producing mineral fibre insulation nearly one hundred years ago, and the brand name was eventually used by many to denote mineral fibre insulation, regardless of the manufacturer. For a number of years, the North American subsidiary brand was Roxul but is again Rockwool.

Does Not Burn

Regardless of the manufacturer, the key benefit of mineral fibre insulation - either as a soft batt or a semi-rigid board - is its noncombustibility. Tested at 750 degrees Celsius, mineral fibre insulation does not burn. Additionally, the material does not pass that heat through to the other side. Many wall assemblies are listed by the Underwriters Laboratory of Canada to resist fire for at least two hours, and the mineral fibre insulation contributes to that protection.

Mineral fibre exterior insulation in your house installed correctly will provide protection to your walls against the extreme heat of a wildfire, and there is a very low likelihood that the heat will cause your wall structure to catch fire.

Remember, you still need to address the roof, windows, doors, and vents. The walls, however, will be comparatively safe if you've provided a few inches of mineral fibre insulation.

This exterior insulation also has the benefit of being mold-resistant and moisture-resistant.

Are you considering replacing the siding on your house? This would be an excellent time to add protection that could be a part of what saves your home from being destroyed by wildfire. Book a free 30-minute consultation with me using the button below, and you'll learn the next steps to take to fire-hardening your home.

If you're not ready to talk with an architect, you can read my more detailed article on fire-hardening your house: "How Will Ultra High-Performance Protect Your House From a Wildfire?", or you could download my free SAPPHR Strategy Guide in which I lay out the framework for designing homes to the hazards of the future.


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