and How to Assess Your Own
Different regions around the world warrant different foundation types. While stone masonry, concrete blocks and precast poured concrete are the most commonly used methods for creating a support structure for a house, hillsides, rocky or sandy regions might employ stilts or piers, and still other types of terrain might employ steel beams.
What types of foundation systems are there?
- Slab-on-Grade (Slab): These foundation types are good for areas with high water tables and if they are protected against frost with insulation on the underside and perimeter walls, they can be inexpensive to build in cold climates. In addition, if finished without any top coverings (decorative concrete finishes), slabs are a great thermal mass for passive solar heat storage, absorbing the sun's heat during the day and radiating it back into the space at night. Slabs also work well with radiant floor heating.
As for new applications of energy-efficient slab foundations, shallow frost-protected foundations (SFPF) have been effectively used in Canada and northern Europe for decades. SFPFs are a clever, and cost-effective variation of slabs with heavily insulated perimeters designed for cold climates.
- Crawl Spaces: Though a popular and inexpensive choice for avoiding excavation costs, crawl spaces have all the moisture and ventilation drawbacks of a basement foundation without the benefits. Since codes require crawl spaces to be ventilated to the outside, they can bring in moisture and health issues. If mechanical equipment is stored in the crawl space, you should make sure that the space is sealed, insulated and ventilated (WIVed).
- Basement Foundations: These foundation types are dug deeper underground than crawl spaces or are partially above and below ground, such as walk-out-basements (suitable for sloped lots). There are several new technologies and foundation products out today. Personally, I am very partial to Insulated Concrete Forms or ICFs (shown below), for ease of installation, insulation value, moisture control, durability, comfort and cost.
Smart design would incorporate a walkout basement that is bermed into the ground on three sides, so that it can take advantage of the earth's constant temperatures below the frost line. This would use the earth as insulation while incorporating a good perimeter drainage system. While basements are a great way to double the size of living spaces, remember that they are often poorly insulated and have moisture issues.
- Pier Foundations: Piers or stilts are usually used for homes that sit on steep or shifty land and have a bit of "give" to them. You may have noticed them supporting houses near bodies of water or warmer areas. Though they use minimal amounts of material compared to other methods and cause lower site disturbance, homes that sit on piers require heavy floor insulation and extra sealing for colder climates. Note that if your home is sitting on fill (not native soil), the piers have to penetrate down to native soil, in order to be stable. Also note that sometimes that requires drilling very deeply, and can end up costing much much more than a conventional foundation.
Different foundation types such as crawl spaces or slabs affect your home's interior climate by how they are coupled to the home structure through the floors and exterior walls. Once you have identified your type of foundation, you must determine if the space is unconditioned, conditioned, or unintentionally conditioned:
- Unconditioned Basement
Unconditioned basements do not have heating or cooling, and are not used as living space.
- Conditioned Basements
Conditioned basements have heating or cooling, the walls are generally finished, and the space is part of the living space of the house.
- Unvented Crawlspace
The house is on a raised foundation, with 2 to 3 feet of airspace under the floor. Unvented crawlspaces do not have open vents to the outside, and are typically warmer than vented crawlspaces.
- Vented Crawlspace
The house is on a raised foundation, with 2 to 3 feet of airspace under the floor. Vented crawlspaces have open vents to the outside, so the air under the house is close to the same temperature as outside air.
Now, for another important part of the equation:
- Is the foundation of your house insulated?
Foundation insulation is insulation added to the foundation's sides to reduce the amount of heat transferred through it. Most houses do not have enough or any foundation insulation.
- What is the R-value of the floor insulation above the basement or crawlspace in your home?
R-Value is a measure of the resistance of insulating material to heat transfer. The higher the R-value number, the more effective the insulation. Unless the insulation is visible, it is typically burdensome to determine what you have, and how much R-Value you are squeezing from it.That said, if you see exposed walls, broken or disconnected foam boards or ceiling joists that are bare, then you will need to repair or add insulation to those areas. If your home is old and subject to humidity and moisture in the basement, assume that you will need to take moisture-control measures before adding insulation.
Next, go to: Examples of Energy Efficient Foundations - I show pictures and talk about problem basements and how they were resolved.
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