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A two-inch layer of sand goes on top of the vapor barrier, followed by a 6×6-inch wire-mesh grid that reinforces the concrete. Typically, a six-mil polyethylene sheet provides a vapor barrier between the soil and the slab. Dirt is compacted and backfilled with four to six inches of gravel. When building slab foundations, the concrete pour comes after the footings have set and before walls are erected. With poured walls, a pencil vibrator is inserted into the slurry to vibrate the concrete into place and ensure there are no air pockets or voids left in the wall. Stem-wall slab foundations prevent water intrusion and the separation of the slab from the substrate that can be caused by uplift or hydrostatic pressure.īoth poured and block foundations are reinforced with rebar.
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When building stem walls, block courses on footings are set below grade and reinforced with rebar before concrete is poured in a continuous pour for a seamless, integral slab.
![floating foundation #2 floating foundation #2](https://i.ytimg.com/vi/YGow6CDCas4/maxresdefault.jpg)
Concrete is then poured into the mold to form the walls.īlock walls can also be used to form stem walls that support a slab above. Once the forms are set, rebar is placed vertically inside the wall channel to support and add additional strength to the concrete wall once the molds are removed. When pouring an integral foundation, aluminum or insulated wall forms are placed on the footings, clamped together, and supported to maintain their shape while the concrete is poured. Poured concrete is more popular for basement construction than block because it is seamless and resists water intrusion. A footing trench ranges from six inches to three feet deep, depending on the building size and soil characteristics. Footings provide a firm surface to resist sinking or shifting into the ground or substrate. These trenches are wider and longer than the walls they support and function like feet to distribute the weight of the wall and the structure above it. Footings are constructed in trenches dug beneath the level of the basement floor. Poured and block foundations both sit on concrete footings, or poured pads that serve as a base for the walls. Climate, including high water tables, frost lines, harsh winters, and vulnerability to storm surge and high winds, will determine whether a slab or below-grade foundation is chosen. When building a house, two main types of foundations are used: slab-on-grade or below-grade foundations with a basement slab.