Garage addition project: part 3, the foundation

Getting the foundation right is critical for a home addition project to run smoothly and quickly. A foundation that is installed out of square or unevenly can cause delays during each subsequent phase of construction as corrections are made to accommodate the improperly installed foundation.

Starting with the concrete footing

As discussed in the previous video text, the concrete footing is formed or trenched so that it ends up being about 24 inches below your frost line. In cases where back-fill is added against the foundation, the footer may be at the existing grade and may only need to be formed.

The width and depth of your concrete footer is determined by the weight and type of structure being built on it. These factors also determine the amount and size of the rebar or reinforcing rod that is installed in the footer and the strength of the concrete used. Your contractor should be able to get all of this information off of the blueprints.

What type of foundation for your addition?

The foundation being poured in the video allows the concrete slab to be up at finished grade and is going to be filled in with dirt and gravel before the slab is poured. Your building may have a foundation like this or it might have:

• A full in-ground basement with full height concrete walls
• A partially buried basement with a short concrete wall in the rear
• A walkout basement with concrete walls on the front and sides and a framed wall in the rear
• A crawl space
• No foundation, just a slab on grade

If you are going to have a basement foundation, your contractor can create openings for windows and doors before pouring the concrete in the foundation wall forms. If you want windows, it's a lot easier to form them now than it is to cut them in later.

Discuss your foundation with your contractor to be sure appropriate attention is given to this important step in the construction process.