How to calculate the cost of building a basement

Updated February 21, 2017

If your new home will have a basement, there are some basic ways to estimate the cost of completing it. While basements are still one of the least expensive construction projects when figured on a square foot basis, finished basements are still a substantial investment. Follow some simple guidelines when determining the cost to build a basement.

Figure in the cost of the excavation. You may not realise that excavation is a major cost to build a basement. This is a substantial chunk of change and it will vary depending upon the type of soil to remove. If the building site has many rocks, the price will be higher. Ask the excavator to look at the site and give you a price per square yard for dirt removal. Make sure he includes his equipment transportation fees and charges for footings.

How much does it cost to pour a basement? Estimate the amount of concrete needed in cubic yards. Determine the amount by figuring a minimum of an 8 inch thick wall for standard construction or a 10 inch thick wall if your house will later have brick or masonry applied to the exterior. A basement with 8-foot high ceilings will need a 9 foot concrete wall.

Add the concrete needed to pour footings, on which your basement walls will sit, by figuring a 2 foot strip of 1 foot thick concrete underneath all portions of your proposed basement walls. Check with your local building code inspector to see if you must pour larger footings in your area.

Find the volume of concrete needed for the floor if poured to a depth of 4 inches. Add this to your concrete figure.

Calculate the reinforcing steel that will give your basement walls strength and integrity. All basement walls contain rebar. Figure on installing one vertical rebar, 94 inches high, every two linear feet inside the basement wall and plan to use nine horizontal levels of rebar. Add rebar ties for connecting in your calculations.

Finish your rebar calculations by calculating rebar reinforcement rods that will run all the way across the floor in both directions on 2 foot by 2-foot centres. Again, add the rebar ties needed to fasten the bars.

Allow for adequate sand in order to stabilise the concrete floor by filling in a minimum of 3 inches before pouring the concrete. In addition, depending upon code, you may have to use sand to backfill around the basement to prevent movement. Sand provides 100 per cent compaction and as such, is often required in areas where the ground shifts.

Check the price of drain tile to install around the perimeter of your basement and add a sump bucket to filter water away from your foundation. If you are in an area where sand must be used to backfill, calculate the price of installing rock over the drain tile to keep the sand from filtering into the perforations and clogging.

Put together the cost of hiring labourers and skilled workers to help build your basement. Pouring concrete walls is labour-intensive since concrete sets up quickly and once set, is no longer workable. Concrete foundations must be poured in a continuous run to make sure there are no "cold joints" that weaken the wall.


Consider hiring a basement contractor if you're not up to the job of building a basement yourself.

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About the Author

Glenda Taylor is a contractor and a full-time writer specializing in construction writing. She also enjoys writing business and finance, food and drink and pet-related articles. Her education includes marketing and a bachelor's degree in journalism from the University of Kansas.