Proposed Change 1809

The provisions found in Clause 9.18.6.2.(2)(a) of Division B of the National Building Code of Canada (NBC) 2020 do not clearly state what is meant by ground cover being evenly weighted down in a heated crawl space.

Ground cover has been shown to balloon as the result of having ballast of incorrect or inconsistent thickness covering it; for example, this ballooning can occur during common operations like running a clothes dryer in a dwelling. This ballooning can cause the soil gas barrier to fail, which leads to soil gases, such as radon, leaking into the livable space of the building. These gases affect the indoor air quality, and the presence of radon can cause an increase in the probability of the building occupants developing lung cancer.

This proposed change clarifies the type of ballast material that can be applied over the ground cover in a heated crawl space and the thickness of the ballast material, which can be measured by the authority having jurisdiction during construction. This clarification would reduce the probability of a premature soil gas barrier failure, which would reduce the probability of soil gases, such as radon, leaking into the livable space of the building.

Currently, it is common practice in construction to use granular material as ballast over ground cover in heated crawl spaces. However, the granular material is not always applied at a thickness of 50 mm. If increasing the thickness of the granular material were required to comply with this proposed change, costs would increase by between $0.70/m² and $1.03/m² for every 25 mm of thickness.

Where sand has been used as ballast instead of granular material, the cost difference ranges from $0.66/m² to $0.88/m² less for a 50 mm thickness of sand compared to using the same thickness of granular material. However, because sand does not drain as well as granular material and can cause mould growth in a heated crawl space, it is not a suitable substitute for granular material.

The benefit of applying the ballast is a reduction in the probability of the ground cover ballooning, which can cause the ground cover seams to fail. It costs between $300 and $400 to repair damaged ground cover due to ballooning.

The proposed change would reduce confusion during inspection about acceptable ballast materials and thicknesses for weighting down ground cover.

This proposed change would affect building occupants by reducing the risk of soil gases and moisture leaking into the building and causing adverse health effects.

For contractors, this proposed change would clarify the requirements for ballast over ground cover and reduce the amount of remedial work that would have been required previously.