Structural Materials: Foundations
A building’s foundation is extremely important to its longevity and performance. As such, it is often the one element where homeowners and builders will tend to choose the tried-and-true techniques and avoid “experimentation.”
This is unfortunate, because the conventional methods and materials typically involve the highest environmental impacts and often the lowest energy efficiency. Most North American homes use vast amounts of concrete in their foundations, and concrete is a perfect example of the kind of energy-intensive building material that has led us to our current environmental state. The production of the Portland cement that is the “glue” in concrete requires using large quantities of fuel to heat limestone to very high temperatures to change its chemical composition. In the process, the carbon dioxide trapped in the stone is released into the atmosphere (along with additional CO2 released by the fuel used to heat the rock). Cement manufacture is one of the world’s leading sources of greenhouse gas emissions. Concrete foundations are commonly paired with the use of petrochemical foam insulation and waterproofing materials, which furthers the ecological and health damages associated with conventional foundation options.
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In considering more sustainable foundation systems, a builder is forced to consider a number of challenges to typical expectations. In many parts of North America, foundations have been twinned with conditioned, subgrade living space: the basement. In those markets, having a basement is so normal that it can be hard to convince a homeowner to imagine a house without one. Creating a basement foundation almost always requires the use of materials that are not sustainable, and if you have high goals for embodied carbon and ecosystem impacts, it will be difficult to meet them with a basement. One benefit to moving away from conditioned basement foundations can be reduced cost. The savings that can be realized by using a more sustainable, grade-based foundation are substantial.
As you will see in this section, there are many ways to create stable, long-lasting foundations that have reasonable environmental impacts. Many of them, however, do not make basement foundations, and those that do come with significant labor requirements. The fact of the matter is that building large, conditioned basements has been a privilege of having cheap energy at our disposal and no concern for climate change. We are nearing the end of commanding that privilege.
It is important to remember that the various foundation systems included here will likely require water control and thermal control layers that are not inherently part of the foundation, and that the materials used for these layers must also be considered against your Criteria Matrix in order to rate the foundation system as a whole.