How Thick Do You Pour a Basement Wall?

Standards

• The absolute minimum thickness for a foundation wall is 6 inches. This is only permitted, normally, for a wall that is no higher than 4.5 inches. For the average two-story American house, 8 inches is the standard thickness. However, the height of a house, the weight and kind of soil, as well as the height of the basement wall itself are the other variables to consider.

Soils

• Soil types are essential for figuring basement wall thickness. The average American soil exerts about 60 lb. per square foot on a basement wall. The moisture content of the soil, the ability to drain it, and the size of the “grains” of soil are all significant variables as well. The pressure put on a foundation wall might be much heavier than 60 lb. For heavier soils, 10 inch walls are recommended.

Concrete Strength

• The concrete used should be at a minimum rated at 3,500 lb. per square inch of strength. Many builders use a 4,000 lb. rated concrete. Normally, the soil hits the foundation wall about 6 or 7 inches, leaving a few inches above ground. This, with an 8 foot basement wall, requires 10 inches of concrete normally. The higher the basement wall and the amount of soil pressing on it are major variables. Basement walls over 8 feet are normally not permitted.

The Home

• A three-story house usually requires a 12-inch basement wall. The vertical weight here would be well over the average of 6 lb. per square foot. The dead vertical load of a three-story house can be well over 12 lb. per square foot, and this usually requires a minimum wall thickness of 10 inches.

  If a house is built on a hillside, the walls have to be much thicker. Since the house is bearing some of the weight of the hill, these walls should be about 12 inches thick. This does not mean that the other side of the house is the same. Depending on the environment, wall thicknesses can differ in the same house depending on the pressures such as hillsides. In that case, the wall directly facing the hill is heavily reinforced with steel bars no more than a foot apart with a minimum thickness of the wall at 11 inches. To some extent, putting the steel reinforcing rods closer together may also give some leeway in wall thickness.

Footing Depth

• The footing depth is also included in thickness calculations. The normal depth for the base of the foundation is about 12 inches. In some cold climates, bases are usually about 18 inches. The deeper the footings, the thinner the wall. An 18-inch foundation footing can permit an 8-foot high wall to remain at 8 inches of thickness for a two-story house. With heavier soils, especially moist soils, the thickness normally goes from 9 to 10 inches.