Eclectic Homes

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

In many respects the base is the most important element of any building, be it a home or a high-rise. In other words, the base is exactly what rests on. So getting the base right will go a long way toward having a sound and stable building for many years.

By pilings into piers to spread footings and more, foundations could be constructed in many ways. The most common, however, is the simple base wall made of poured concrete or concrete block, along with a poured concrete footing system. The vast majority of houses in North America are constructed using this strategy, as it is relatively inexpensive and you will find scores upon scores of tradespeople able to quickly and efficiently build it. As a result, the focus of this item is on the normal wall and footing foundation system.

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

Bud Dietrich, AIA

Both structural sections of this kind of base:
A continuous concrete footing
A base wall of poured concrete or concrete masonry units (CMUs)A concrete flooring slabThese three components are the base system’s structural components, serving to move the gravity load (the weight of the house) down to the floor. While concrete is an perfect material to handle the weight of the home, concrete isn’t very flexible. So steel reinforcing bars have been introduced to the cement to help withstand any bending or twisting due to ground motion.

An essential design consideration is placing the bottom of the footing below the frost line. This line exists at a certain distance beneath the surface and is where the ground, or any moisture in the ground, doesn’t freeze. Putting the footing below the frost line is imperative to protect against any heaving or alternative motion brought on by the freeze-thaw cycle.

Notice that the depth of the frost line varies by location. The frost line is closer to the floor surface in warmer climates and even deeper in colder climates. Nonetheless, it’s vital to know where your frost line is if designing your house’s base.

Bud Dietrich, AIA

Maintaining water out. A base system is in many ways just like a huge bathtub. But instead than keeping water in, we want to keep water out. Several components built to a base do just that.

First, the exterior, ground-side surface of base walls will have a waterproofing material installed on it. This material ought to be strong enough to stop punctures or tears and flexible enough to allow for any motion the base will encounter. This moisture barrier ought to form a skin not only within the wall but in the top of the footing as well.

Next on 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 also be channeled away from the footing. Ensuring that these drains are apparent is a critical step in ensuring water doesn’t get in the cellar or crawl space.

Additional Areas of the waterproofing method:
A polyethylene vapor barrier installed between the concrete floor slab and the floor to keep ground moisture from migrating into the slabA finish level that slopes away from your base in order that water drains away from, not toward, the houseA floor level of at least 6 inches below the top of the base wall

Bud Dietrich, AIA

A nice touch for brick exteriors. There are many variations in any base system. 1 version is that the incorporation of a brick ledge to the base wall design. This is a wonderful design detail if you’re planning on using an exterior brick or stone finish. As opposed to the brick sitting on top of the base wall, the brick could start just below the finish grade, making it seem that the base is constructed of brick, since it would have been at an older home. Of course, this type of detail must be worked out carefully so that the base remains dry over the long haul.

Just make certain that you and your architect or builder work out the very best base system for your individual project. Having a good, secure and strong base that remains dry will be well worth every cent spent in it.

Next in Know Your Own House: What Makes Up a Floor Structure

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