Know Your House: What Makes Up a Home's Foundation

Learn the components of a common foundation and their purpose to ensure a strong and stable house for years to come

Bud Dietrich, AIA

Houzz Contributor. 

In many respects the foundation is the most important element of any building, be it a house or a high-rise. Simply put, the foundation is what everything rests on. So getting the foundation right will go a long way toward having a sound and stable building for many years.

From pilings to piers to spread footings and more, foundations can be built in many ways. The most common, though, is the simple foundation wall made of poured concrete or concrete block, and a poured concrete footing system. The vast majority of homes in North America are built using this approach, as it's relatively inexpensive and there are scores upon scores of tradespeople able to quickly and efficiently build it. Therefore, the focus of this piece is on the typical wall and footing foundation system.

And remember that you should consult a local architect or builder to review any planned foundation and how local building codes will impact the system design and construction.

by Bud Dietrich, AIA »

The three structural parts of this kind of foundation: A continuous concrete footing A foundation wall of either poured concrete or concrete masonry units (CMUs) A concrete floor slab These three elements are the foundation system's structural components, serving to transfer the gravity load (the weight of the house) down into the ground. While concrete is an ideal material to handle the weight of the house, concrete isn't very flexible. So steel reinforcing bars are introduced into the concrete to help resist any bending or twisting caused by ground movement. A very important design consideration is placing the bottom of the footing below the frost line. This line exists at some distance below the surface and is where the ground, or any moisture in the ground, doesn't freeze. Placing the footing below the frost line is essential to prevent any heaving or other movement caused by the freeze-thaw cycle. Note that the depth of the frost line varies by location. The frost line is closer to the ground surface in warmer climates and much deeper in colder climates. But it's essential to know where your frost line is when designing your home's foundation.

by Bud Dietrich, AIA »

Keeping water out. A foundation system is in many ways like a big bathtub. But rather than keeping water in, we want to keep water out. Several components built into a foundation do just that. First, the exterior, ground-side face of foundation walls will have a waterproofing material installed on it. This material should be strong enough to prevent punctures or tears and flexible enough to allow for any movement the foundation will experience. This moisture barrier should form a skin not only over the wall but at the top of the footing as well. Next in the line of defense against water is a perimeter drain near the bottom of the footing. This drain is a perforated pipe surrounded by crushed stone to keep dirt and debris from blocking the perforations. Groundwater will find its way to this drain and be channeled away from the footing. Making sure that these drains are clear is a critical step in making sure water doesn't get into the basement or crawl space. Other parts of the waterproofing system: A polyethylene vapor barrier installed between the concrete floor slab and the ground to keep ground moisture from migrating up into the slab A finish grade that slopes away from the foundation so that water drains away from, not toward, the house A ground level of at least 6 inches below the top of the foundation wall

by Bud Dietrich, AIA »

A nice touch for brick exteriors. There are many variations in any foundation system. One variant is the incorporation of a brick ledge into the foundation wall design. This is a nice design detail if you plan to use an exterior brick or stone finish. Rather than the brick sitting on top of the foundation wall, the brick can start just below the finish grade, making it appear that the foundation is constructed of brick, as it would have been in an older home. Of course, this type of detail has to be worked out carefully so that the foundation stays dry over the long haul. Just make sure that you and your architect or builder work out the best foundation system for your particular project. Having a good, stable and solid foundation that stays dry will be worth every cent invested in it.  Let World Class Supply help you with your green building materials!