Raised Floor Foundation vs. Slab-On-Grade

There are two commonly used types of foundations in light frame construction. One type is frequently called a raised floor, which is a continuous spread footing that runs the entire perimeter of the building with piers down the middle. The other type is a slab-on-grade or slab foundation; this foundation type is a single slab of concrete that serves as the floor of the building, which is poured thicker around the perimeter to form a footing. Some projects use both types of foundations i.e. a raised floor foundation house with an attached garage would have both types of foundations. The main foundation should be chosen based on the particular needs of the build site, but can also be determined based on investment variables.

A raised floor foundation has many pros and fits most project applications. If the building site has problematic soil, such as expansive clays, a raised floor foundation would perform much better than slab, as slab would most likely crack on this type of soil. A raised floor is also used to raise the building above a floodplain. The most practical reason a raised foundation is good is because it allows for a crawl space underneath the building, which allows easy maintenance, repairs and remodels. A few drawbacks to using a raised foundation are the higher cost and the potential termite threat to the exposed wood near the ground.

A slab foundation has many pros as well, but is only beneficial in some project applications. A slab foundation is easier to construct when the grade of the build site is very low, meaning that there is little to no slope. It can help protect the home from termites, as there is no exposed wood with a slab foundation. A slab is much cheaper, and can be beneficial to elderly or disabled persons as there are fewer steps. However, slab too has drawbacks such as, it is very difficult to remodel and very expensive to repair should it crack.

Each build site is unique, and the main foundation should be chosen to fit the build site. However, for long term investments, it seems that a raised floor foundation would be the best option.

This is an example of a raised floor foundation / framing. One can see the continuous stem wall and footing around the perimeter and the piers down the center to carry the load of the girder.

This is a section through a slab foundation. One can clearly see the thicker portion at the edges that would run the perimeter of the building.

- Amber Edge Drafting


#raisedfloorfoundation #slabongrade #foundation #pros #cons

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