Home Foundations: Making Sure You Know the “Base-ics”
A home is only as strong as it’s weakest link and getting the foundation right keeps the rest of your home upright.
There are several different types of home foundations. Why is this important? A home is only as strong as it’s weakest link and getting the foundation right keeps the rest of your home upright. If you’re buying, building or updating your existing home, starting on the right footing keeps you from having to make costly repairs or investments elsewhere.
The foundation a home needs, or has, depends on several factors:
-The load capacity. Some foundations are only meant to hold a certain amount of weight. Exceeding that load-bearing capacity can result in some very unfortunate results, like complete foundation and house failure or collapse. Read this article to learn about some tell-tale signs of foundation failure. Playing pick-up sticks with your home is never fun!
-Groundwater. If a home’s foundation is over-exposed to groundwater, it can weaken your home. Foundations should be built in an area with good drainage; in some cases, this can simply mean on top of a hill. In other instances, this means using gravel or grading or sloping the area around a home to drain water away. Other types of foundations may lift a home off the ground. However, some foundations can’t be used in areas where the ground remains too saturated.
-Climate and risks. Different climate zones and local risks determine the type of foundation a home will need. A home in an earthquake-prone area will be designed with a different foundation type than a home in a hurricane-prone area. Same goes for areas with extreme temperature ranges. Places that freeze, areas with heavy rainfall or that may flood, require different foundations and materials.
After these factors are considered you and your contractor (and at times, in consultation with your local Building Code Inspector) can decide what foundation to use. You should also take these items into account when purchasing a home, because sometimes they may not have been considered when the home was built.
There are three primary foundation types - slab, basement, and crawlspace. We added stem wall and elevated homes because these are becoming popular choices for many reasons and we recommend homeowners consider them depending on their location and the hazards they are exposed to. There are variations of each type of foundation type and you should talk with your contractor, engineer or inspector about which one is right for your area and home design.
-Slab on Grade foundations are concrete poured over a grade (prepared area for a foundation that is level) and strengthened with a metal grid of rebar of which the concrete is poured over. This technique is usually used in warm climates that don’t freeze (freezing can cause cracks in the concrete). With this technique, there is no crawl space or basement and piping is often encased in the slab.
-Stem Wall foundations begin by pouring a footing below grade. They then extend above grade and are typically filled in with earth or gravel. This can be used to increase the height of the homes first floor, elevating it but not leaving open space beneath the home. Stem walls are a popular foundation type in areas where frost is a concern but are becoming more popular in high wind and hurricane zones because they provide more secure anchorage points for walls when considering engineered load paths.
-Crawlspace foundations are when the home is built on pilings of some sort leaving space between the home and the ground. This allows piping or wiring to be run under the house and be accessible. It can protect the home from flooding if raised above the base flood elevation. There are many kinds of pilings that can be used; concrete, bricks or blocks and mortar, or even just wood.
A BIG Note - If you build a home with a crawlspace, we recommend making sure it is anchored to the rest of your home and NOT using a “dry stack” foundation or dry stack piers. A dry stack is comprised of stacked bricks or blocks and the home's structure is built on top using joists. Many times there is no mortar between the blocks of the dry stack piers, no strapping holding the house to the foundation. Gravity is the only thing “holding” the house to its “foundation.” Basement foundations are typically excavated and built into the ground — these types of foundations of waterproofed and sometimes are fully completed into more living or storage space. A basement foundation isn’t recommended for areas that are susceptible to flooding.
Elevated homes do not require what many people typically think of as a foundation. Homes that have been elevated on concrete or wooden piers (often called stilts) have been secured into the ground using a series of concrete footers poured or drilled deep into the ground. This ensures the home is anchored securely. Elevated homes typically then have “breakaway” components beneath them (we recommend this approach regardless); staircases, storage areas, etc. Many areas have rules, or codes, that do not allow for permanent fixtures or rooms to be kept below in areas where homes must be elevated. This is because the risk of flooding or storm surge is too great. If these areas are flooded, these elements are designed to break off, leaving the main, elevated home intact.
For a more detailed description of each of these types, visit this website. See a detailed list of pros and cons of each foundation type here. Learn what FEMA has to say about elevated homes and stem walls here. Finally, if you add onto your home, don’t forget the foundation! Ensure your contractor or engineer ties in the new foundation to the old and that it can support the weight of the all new construction.