Are Cordwood Walls Fire-Resistant or Not?

Fire Resistance in Cordwood Walls

Cordwood walls are made from hollowed-out logs that are stacked and held together with a mixture of mortar and insulation. The logs are typically hollowed out to a depth of about 1-2 inches, which helps to reduce the overall amount of wood used in the wall. This hollowing process also creates a space that can be filled with insulation, such as vermiculite or perlite, to help prevent heat transfer and reduce the risk of fire spreading.

Mortar Mix and Fire Resistance

The mortar mix used in cordwood construction is also designed to be fire-resistant. Typically, a mixture of 1 part cement to 2 parts sand, with a small amount of lime added for additional durability, is used. This type of mortar mix has a high compressive strength and is less prone to cracking, which helps to prevent gaps that could allow fire to spread. Additionally, the mortar mix can be formulated to have a high degree of fire resistance, with some mixtures containing additives such as silica or calcium carbonate that help to slow down the spread of fire.

Construction Techniques for Improved Fire Resistance

To further improve the fire resistance of cordwood walls, builders can use various construction techniques. For example, using a dry-stacked cordwood approach, where the logs are not mortared together, can help to reduce the amount of flammable material in the wall. Alternatively, builders can use a mixture of cordwood and other materials, such as brick or stone, to create a more fire-resistant wall. Additionally, incorporating a layer of insulation, such as foam board or spray foam, on the exterior of the cordwood wall can help to reduce heat transfer and prevent fire from spreading.