When you undertake the construction of a new home it is necessary to calculate the amount of concrete needed to build the foundation. In order to provide the supplier with an accurate estimate, the volume of the foundation must be calculated in cubic feet; 27 cubic feet is equal to 1 cubic yard of concrete.
There are 2 basic types of concrete foundations: 1) slab-on-grade and 2) foundation walls on footings surrounding a full basement. A slab-on-grade consists of a concrete slab (typically 4 inches thick) and a grade beam around the entire perimeter and under the load bearing walls. The foundation for a full basement consists of 3 primary components; the slab, the foundation wall and the footing on which it rests. This article will explain an easy method for calculating the volume of concrete needed for both types of foundations.
Calculate the Volume of a Slab-on-Grade
First, divide the entire volume of the foundation in rectilinear segments and calculate the volume of each separately. Say, for example, the foundation is a slab on grade 50 feet by 100 feet by 4 inches thick with a 12 by 8-inch grade beam along the perimeter. Remembering that 1 inch is equal to .083 feet, convert the 4 inch thickness of the slab to feet, and calculate the volume of the slab as follows: .332 feet x 50 feet x 100 feet = 1660 cubic feet. Next, calculate the volume of the grade beam as follows: 1 foot x .664 feet x 300 feet (the total length of the perimeter) = 199.2 cubic feet. Add the 2 volumes together to get a total volume of the foundation equal to 1859.2 cubic feet. Simplify by converting the total to cubic yards. 1859.2 cubic feet divided by 27 cubic feet is equal to 68.85 cubic yards.
Calculate the Volume of Concrete Needed for a Full Basement
The foundation for a full basement will require a few additional calculations. Take a basic foundation plan of 50 by 100 feet having an area of 5000 square feet (excluding the thickness of the foundation walls). The foundation walls are 8 inches in thickness by 8 feet in height supported by footings of 8 inches in depth by 16 inches in width.
Calculate the thickness of the slab as before: .332 feet x 50 feet x 100 feet = 1660 cubic feet. Do separate calculations for the foundation walls and the footings. The volume of the foundation walls is found by multiplying .664 feet x 8 feet x 300 feet = 1593.6 cubic feet. The volume of the footing is found by multiplying .664 feet x 1.332 feet x 300 feet = 265.33 cubic feet. Add the volumes of each of the components together to get the total volume of the foundation: 1660 cubic feet + 1593.6 cubic feet + 265.33 cubic feet = 3518.93 cubic feet. Simplify by converting to cubic yards. 3518.93 cubic feet divided by 27 cubic feet is equal to 130.33 cubic yards. This is the total volume of concrete needed to construct the foundation.