Green Homes Special Series: Part Seven: Foundations

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A good foundation is important. It helps a house withstand vertical and horizontal loads and protects from frost heaves. Foundation Basics Foundations are typically made of concrete, concrete block, brick or stone with a few even using wood. While there are several types of foundations, the main three are slab, crawlspace and basement. Each type has its own special needs that must be understood. Slab. This is a concrete slab that sits directly on the ground and forms the lowest floor of the house. The slab may be supported by independent footings or integral beams. Crawlspace. This type is generally a continuous perimeter footing with the lowest floor of the house suspended above the ground. The area within the perimeter and between the ground and lowest structural floor component is a space large enough to crawl through. Basement. The excavated space below the main floor supported by footings and with walls and floor. It can be totally underground, as in a full basement, or partially below the surface, as in a garden basement or even in the form of a walkout. Influencing Factors Home foundations differ across the country. Residents in the North may be familiar with full basements, garden basements, crawlspaces or, often in old homes, a combination crawlspace-basement. Those in the South typically have had slab or crawlspace foundations. Each foundation insulation approach has benefits and detriments. From left, interior insulation is the most common and least expensive but has the most moisture problems; exterior insulation would seem best from a physics perspective but has practical problems with protection, thermal bridging and insects; insulation in the middle is the most expensive and most difficult to construct but has the fewest moisture and insect problems; and insulation on both sides has problems similar to exterior insulation with the added cost of the interior layer. Photo courtesy of BuildingScience.com. Many factors influence our choice of a home foundation. Affordability, water tables, soils, climate, even hazards such as earthquakes figure in.

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