A house foundation takes the loads from the roof, walls and flooring and transfers them to the soil for proper support. It’s as important as any other element of construction, especially if you are building a healthy home or using green building techniques.
Not only is there the importance of load bearing and proper construction design, but there is also the issue of how to build a house foundation in order to avoid mold growth and other toxicities that can eventually invade the upper levels of a home.
In general construction, the type of foundation is typically chosen based on local climate conditions and construction conditions of the area. However, when choosing to build a healthy house, there is more to consider such as:
- Moisture control
- Termite avoidance
- Healthy materials
- Soil conditions
- Radon mitigation
- Energy efficiency
4 Basic Types of House Foundations
1. Crawlspace – This is probably the most common and is suitable for all climates. The crawlspace design is generally found, however, in the middle portion of the U.S.
The raised foundation, as it is sometimes called, is built above the ground with just enough space to crawl underneath for installation and maintenance of mechanical issues of the house.
The crawlspace design has stem walls on the perimeters and pierced in-between. A girder system and floor joists are on top of that for a complete crawlspace foundation system.
2. Basement – Basement foundations are most commonly found in the colder areas of the U.S. like the North and East, although they are relatively common in other areas. In colder climates, a completely enclosed basement system that is dug down into the soil is more common. If a home is built on an incline, some basements are partially enclosed with one or all three sides open. This allows for windows and doors to be framed into the structure. A basement allows for additional space for home living.
3. Slab – A slab foundation is more common in warmer areas such as the South or West. It is concrete poured directly on the soil. Perimeter footings are dug, some soil is removed and graded before pouring the cement slab and footings. This type of foundation is more often found in housing developments where a lot of homes are built with similar designs. It’s easy, cheap and efficient to use slabs for foundations. They are often used where the soil condition would not allow for a basement.
4. Pier Foundation – Pier foundations are generally the easiest to build especially for healthy house construction. Pilings or stilts, as they are sometimes called, don’t always look the most uniform in a subdivision or urban housing areas, but they can add an interesting design element when on slopping, hilly or water front properties.
The best practical benefit for using a pier foundation is the fact that the house is lifted off the ground and is completely removed from the soil underneath. Since there’s no direct contact with the ground, problematic issues with radon exposure, termites and mold growth are of much less concern than with other types of foundations.
The piers or pilings themselves can be built of toxic free materials such as steel, concrete, and masonry. Even using insect resistant wood may not cause the same toxic exposure an enclosed foundations because of the air flow and quick degassing possibilities.
Other issues such as termite control, insulation, drainage and foundation coverings are additional items that will require a non-traditional approach. The Healthy House Institute offers these helpful tips when building a pier foundation:
From an energy standpoint, a pier foundation itself doesn’t need to be insulated, but the floor system of the house should be. The floor will, in effect, function just like an exterior wall and it should be insulated, tightly constructed and fitted with a diffusion retarder. A pier foundation can be combined with a variety of floor framing systems: metal or wood joists, wood or concrete subfloor.
Pier foundations must have proper drainage to ensure the surface water is directed away from the structure. If the ground slopes toward the structure, water will run under the house and form puddles; havens for microorganisms or insects such as mosquitoes. A high water table will require an underground drainage system to minimize uneven settlement and frost heaving.
Covering the Foundation
The bare ground under a house built on piers can be unsightly and dusty. A covering of crushed stone or gravel will improve appearance and help control the dust. Because the area under the house is shielded from both sun and rain, weed growth is generally not a problem. Weed growth can be prevented by laying, plastic sheeting under the gravel.
A latticework of wood or metal around the perimeter can sometimes enhance the appearance and make the foundation look more conventional. The space under the house should not be totally sealed with a skirting material—as is done with mobile homes—because it will begin to function like a crawl space and cause build-up of moisture and radon. Leaving the area under house as open as possible is the best and safest option.
The tops of the piers can be capped with a metal termite shield so insects cannot sneak into the house through small cracks or openings in the piers. If piers are made of masonry, and a termite shield is not used, the tops should be well-sealed to prevent radon from rising up through them into the floor system.
While any of the 4 foundations can be built in a healthy way, from a health stand-point, the pier foundation obviously offers more natural air flow, dryness and less effort for termite control that any other foundation type. Again, it is the easiest foundation to build to ensure healthy house requirements.
Choose the Best Foundation for Your Healthy House
It can’t be overstated as to how important it is to choose the right foundation on which to build your healthy home. Many homeowners have had to flee their homes because of faulty foundation structures that leeched harmful toxins into their living spaces.
So, be sure to choose the best foundation for your healthy home with the help of your architect, contractor and/or healthy home specialist.