Despite all of the features most buyers consider when purchasing a house, such as location, number of bedrooms and bathrooms, kitchen appliances, fireplace, porches, etc, the foundation is probably not one of the items addressed, or even considered. Yet, the foundation forms the very basis of the structure. Without a solid foundation on well drained soil, the house will not last for long.
All homes have a foundation, and some foundations are better than others. The type of foundation is often dictated by the area of the country the house is located. Old foundations usually differ from newer foundations. Regardless of the type of foundation, or the materials used, all foundations serve to support the house on the land upon which it is built.
In order to bear the weight of the home all foundations have certain elements. The foundation walls are built upon a ‘footing’, which is usually a thickened area of poured concrete that bears directly on undisturbed soil. The footing serves to spread the load of the foundation walls onto the soil and helps prevent the foundation walls from settling. The foundation walls are then formed and poured (if concrete) or built upon the footing. The foundation walls normally extend about a foot or so above the grade or soil level, so that the wooden parts of the house are raised above the soil and are thus protected from the damp.
The minimum depth of the footing and foundation walls is dictated by several factors. Most critical is the prevailing climate and type of soils. All foundations must extend below the ‘frost line’ in cold climates. In the Midwest, this is commonly 42 inches below grade, but is much deeper further North, and can be shallower further South. Another consideration is the size of the house built. A two story home may require a thicker footing and foundation wall than a single story home.
In the American Midwest, residential construction uses three common types of foundations; basement, crawlspace, and slab on grade foundations. There are other types of foundations but they are rare in the Midwest. The materials commonly used for foundations vary from ‘field stone’, glazed and unglazed tiles, brick, cement block, and concrete. We’ll address each type individually.
Slab foundations are quite simple, consisting of the perimeter ‘foundation wall’ with a concrete slab poured within the wall. The slab should be poured over a layer of gravel, topped with a waterproof barrier, usually plastic sheeting for moisture control. Larger homes will have thickened areas within the slab, or ‘grade beams’ that provide support for interior walls as well. Within the slab there is often the drain and waste piping, water supply piping, heating ductwork and electrical wiring or conduit. Once the slab is poured and the utility pipes and ductwork are sealed in, repairs are difficult and expensive.
Crawl space foundations are built over a shallow excavation that varies in depth, but is commonly about 36 to 40 inches deep. After the excavation is dug, the footing and foundation walls are built. Interior supports are provided by strategically placed “footings” that support columns for the girders or beams that support the interior floors and walls. The better crawl space foundations have a concrete floor poured over a layer of gravel and plastic sheeting, which helps to keep moisture under control. If the floor is earth, a plastic sheeting moisture barrier is essential for moisture control.
Basement foundations are quite common in the Midwest. The excavation is generally 8 feet deep, which yields a useable basement ceiling height of about 7 feet, 6 inches from the slab to the bottom the floor joists. Again, the foundation is poured or built upon the footing, and a floor slab is poured over a gravel base topped with plastic sheeting. Basement foundations have the advantage of providing useable space for utilities, mechanicals systems, and storage not available in the previous two types of foundations. Many homeowners even finish all or parts of a basement into living space. Doing so can provide much needed additional space in a smaller house, but care should be taken to avoid water problems. See the article on Finishing Basements elsewhere on this website.
Materials used for foundations were briefly discussed above. Generally, construction since the late 1940’s and early 1950’s has used poured concrete and cement block as the more common construction materials for foundations. Poured concrete is probably a little better at preventing moisture intrusion overall, but block is quite satisfactory in well drained soils. In homes built prior to the War more foundations were built with brick and tile. In rural areas, many foundations are stone, either dry laid or laid up with mortar. These older types of foundations are almost always prone to seepage or leaking during wet periods and many require periodic maintenance such as tuck pointing to maintain the mortar joints.
Controlling water within the foundation did not seem to be a primary concern in pre war houses (basements were never meant to be finished). These homes often did not have deep foundations and sump pumps were rarely installed. Seepage drained to a floor drain, and the home dried out naturally if seepage did occur. Since the late 1950’s into the 1960’s, finished basements became more popular, and house construction became ‘tighter’. Water intrusion needed to be controlled, and foundation drain tile and sump pumps became almost ‘standard equipment’ in crawl space and basement foundations. This is a system that employs porous ‘tile’ – usually perforated flexible plastic pipe – installed around the house at the level of the footing. Water in the soil enters the tile and is routed to a sump pit in the basement or crawlspace. A pump then pumps the water out and away from the foundation. This helps prevent the buildup of water pressure in the soil around the foundation, and helps keep the basement or crawl space dry. Properly maintained, this system does a good job.
In inspecting the foundation, your home inspector will inspect the foundation and other visible structural elements of the home, describe the type of foundation and materials used, and report any defects noted. Common defects are cracks in foundation walls, bulging, leaning, or displaced walls, water intrusion through the foundation walls and deterioration of the materials used. In cases of obvious or suspected foundation failure or settling, the inspector will recommend the services of an engineer or qualified foundation contractor. Because the foundation is so important to the home, be sure to ask questions if you are unsure of anything in the inspection report, and always follow up if the inspector recommends further review of a foundation problem.
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