Project Guide

How to Build a Foundation

1
Types of Foundations
The concrete slab for a basement foundation.

The foundation ensures that a house stays where it’s supposed to be.


There are three general types of foundations. Wide regional differences in foundations can be explained by climate. In New England, most homes have basements, while warmer locations in the South are likely to have crawl spaces or slab foundations.


Overall, concrete slab house foundation are the most common type. These foundations are made from poured concrete – usually between four and eight inches deep – and reinforced with steel bars called rebar.

 

Basement foundations have subterranean concrete walls that support the above-ground structure. Benefits include additional square footage for the home but the extra labor and materials needed to build a basement foundation make it the most expensive version.


Crawl space foundations have concrete footings beneath the ground with short concrete walls that extend a few feet above the surface for the house to rest on. This type is common in the Pacific region of the country.


All types of concrete foundations must have secure footing, the most important component of a foundation. Footings support the foundation, which supports the house.


Foundations are designed around the soil conditions and the size of the building to be built in order to prevent heaving and buckling. The depth and dimensions of the footings and type of foundation depend on a number of factors.


Considerations include the depth of the frost line in the region, water tables, flood zones, the type and stability of soil, as well as slope and drainage of the site. Local building codes will also have requirements.

2
Building the Foundation
A wall made from cinder blocks for the foundation of a home.

Excavation can begin after footing and foundation size calculations are determined.


Pressure-treated lumber is used to build forms for the footings and rebar is installed within the forms to reinforce the concrete. The forms are staked into the ground to remain in place when the concrete is poured. It is critical that the top of the forms are level. When the footing concrete has cured, the forms are removed.


The next step depends on the type of foundation being built. Courses of cinder block and mortar can be added until the top of the foundation is reached or a concrete wall might be cast using wooden forms similar to the process used to make the footings. It is essential that these walls are plumb and level.


If it is a slab foundation, a layer of compressed gravel is added within the foundation perimeter for drainage, along with a vapor barrier and layer of sand. Wire mesh is laid for reinforcement and concrete is poured within the defined area after conduits are in place for necessary plumbing and electrical work.


Clean and porous backfill is used in the space between the excavated earth and the completed sides of the foundation. At the surface level, the ground is graded to slope away from the house.

3
Foundation for a Garage
A concrete slab foundation.

The overview of how to build a foundation for a house is similar to what is necessary to build a foundation for other structures, such as a detached garage.


As with any type of construction, obtain any necessary permits before beginning a project.

  • Layout the area for the foundation and mark the perimeter.
  • Ensure that no underground utilities are present.
  • Dig out dirt for the footings and slab according to the plans while following building and safety codes.
  • Build forms for the footings and for the slab. Install rebar.
  • Pour concrete footings.
  • When footings have cured, pour the concrete for the slab into the prepared location.