House Foundation Types 101

Worker Installing Rebar for Foundation
© Nenov Brothers / Fotolia

The type of foundation supporting your home has a widespread effect on the building’s durability and on your comfort. Whether you’re planning to build your own home or you want to know more about the house you live in now, getting familiar with foundation design is the perfect place to start.

Three types of foundations are commonly used in modern residential construction:

  • Slab
  • Crawl space
  • Basement

The type that’s right for your home depends largely on the properties of your building site, such as the soil type, water table depth, and slope. Beyond this, each type of foundation has pros and cons in terms of affordability, maintenance, home comfort, and other factors.

Slab Foundation

Concrete Slab Foundation and Home Framing
© Lev / Fotolia

This is the simplest, most budget-friendly, and most common type of house foundation. This foundation is a slab of concrete around 6 to 8 inches thick poured directly onto a soil surface prepared with gravel to facilitate drainage. There are several ways to build a slab foundation.

  • Slab on grade – To construct this foundation, concrete is simply poured onto the prepared soil. It’s poured thicker at the edges to form a footing. Rebar is added for strength and wire mesh might be added to reduce risk of cracking.
  • T-shaped – This foundation consists of concrete footings below the frost line and walls on top of the footings reaching to the soil surface. The slab is poured on top of this supportive structure.
  • Frost-protected (FPSF) – This foundation contains rigid foam insulation to prevent the ground below from freezing, reducing the risk of cracks. It’s used only with buildings that will be heated in winter.

The house is built directly onto the foundation, eliminating the need for a flooring support system, which further cuts costs and speeds up construction.

Pros

No open space under the house means less risk of infestation by termites, mice, and other pests. Because slab foundations don’t rely on beams for support, they’re exceptionally sturdy. They require only minimal digging, so they’re perfect for rocky or heavy soils where digging a crawl space or basement would be impractical.

Cons

Water, natural gas, and drainage pipes are often embedded within the concrete, and when these pipes wear out and leak, the foundation will have to be opened so repairs can be made. Slab foundations are vulnerable to pressure caused by freezing and thawing ground, so they’re best used in warmer climates where the ground rarely freezes. Because they can’t protect the house from flood waters the way a crawl space or basement can, they’re less than ideal for flood-prone areas.

Crawl Space Foundation

Crawl Space Foundation Under Construction
Photo Credit: RBerteig

A crawl space foundation includes an open space of around 2 feet high under the house, which elevates the house off the ground. These are typically built using one of two methods:

  • Stem wall – A continuous masonry wall.
  • Pier-and-beam – Concrete footings in the ground that support wood piers and concrete beams that span between the piers.

Pros

A crawl space foundation is a good choice in an area with a high water table or tendency to flood. It protects the home from shifting soil during heavy rains and, with flood vents added, it will reduce the risk of flood water entering the house. The crawl space provides air circulation under the house, helping to keep your rooms cooler in summer. Pipes and other utility lines are often located here, so you can easily reach them for repairs or upgrades. You can also use the space for storage.

Cons

A crawl space must be properly insulated and maintained to prevent problems with moisture, mold, cold drafts, and pests. Depending on your climate and your home’s design, this could mean adding a vapor barrier and rigid foam insulation in addition to vents or completely encapsulating the space and sealing the vents, then installing a sump pump and dehumidifier.

Basement Foundation

New House Basement Construction
© Christian Delbert / Fotolia

A basement foundation is built by excavating down to around 8 feet, then constructing a floor and walls for the resulting space. First, concrete footings are poured to support the walls. Next, the walls, usually made of poured concrete, are erected. Finally the concrete slab floor is poured. The result is an additional room you can use for storage area or to extend your living space.

Pros

A basement is the perfect place to house appliances related to your utilities, such as your furnace and water heater. You’ll have easy access to these appliances as well as to the pipes and ducts in this space, making it easier to maintain them and make repairs. The basement also gives you a convenient place to put the washer and dryer to free up space in your main living area.

With a little creativity, it can be turned into a workshop for your hobbies, home theater or even a home bar and pool room. As an added benefit, the air space a basement creates under your home helps keep your rooms cooler in summer.

Cons

Once the basement is built, you’ll need to air seal and insulate it to prevent unwanted heat loss and gain. In flood-prone areas, you’ll need to install a sump pump to remove any flood water that enters the basement. Keeping your basement properly air sealed, dry, and clean also helps prevent pest infestations and mold.

If your house will be located on bedrock or limestone that’s close to the surface, digging a basement could be impractical if not impossible. Heavy or water-logged soils, such as clay and wetland soils, are also difficult and often impractical locations for a basement. In these areas, if you want your foundation off the ground, a crawl space is the better option.

Although the kind of land you’re building on is the biggest determining factor in what type of foundation will best suit your home, very often you’ll have some choice. If you do, consider how each type of foundation will affect the building’s longevity and maintenance needs, as well as your enjoyment of your home.

If your home has already been built, keep your foundation type in mind when you plan out your routine home maintenance tasks. For instance, slab foundations should be monitored for leaking water lines, while crawl spaces and basements should be regularly checked for moisture problems and pest infestations.

Posted on Categories Structural