Backfilling Foundations

Backfilling a Foundation takes Patience, Skill and the Right Soil Type

By Mark J. Donovan




Backfilling foundation walls is somewhat of an art. If not done properly foundation walls can be knocked off their footings or cracked. In addition, prior to backfilling a foundation, preparatory work on and around the foundation is critical for ensuring a leak free basement.

When backfilling foundations it is important that the concrete walls first have adequate time to properly cure. In ideal weather conditions it normally takes up to 28 days for concrete to fully cure.

Until then the foundation walls are not at their maximum strength and can be more easily damaged when backfilling.

Consequently in a perfect construction site world backfilling of foundation walls should be held off approximately 1 month from when the foundation walls were poured.

In addition, prior to backfilling a foundation, the exterior walls should be sealed and insulated. Sealing foundation walls, up to the expected finished grade of soil, can dramatically help to prevent ground water from seeping through the porous concrete material and into the basement.

Likewise insulating the foundation walls can help prevent the seepage of warm basement air into the surrounding cool earth.

Also, prior to backfilling a foundation, a perimeter drain should be installed around the foundation footing to help direct the flow of ground water away from the home. In addition, any utility pipes that need to be brought through the foundation walls should be installed and sealed up with hydraulic cement.

Backfilling Foundations

Finally, the basement concrete slab should be poured prior to backfilling. By pouring the concrete slab you can help to prevent the foundation walls from getting knocked inwards when backfilling the foundation.

When actually backfilling a foundation it is best to use coarse grained soil and start in the foundation corners. Backfilling soil should be pushed into place rather than dropped into place. Using existing material from the excavation site is not always wise, particularly if it has high concentrations of clay or decaying matter.

Clay soil does not drain well and decaying matter will lead to eventual depressions around the foundation. In addition, boulders should not be used as they can crack the foundation walls. As the soil is pushed into place around the foundation it should be compacted often.

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Finally, the finished grade should be gently sloped away from the home. The grade should be at least 1 inch per linear foot, away from the foundation, for the first 5 to 10 feet.


For more help on building a home addition, see HomeAdditionPlus.com’s Home Addition Bid Sheets. Our Home Addition Bid Sheets provide you with the knowledge and information on how to plan a home building project, and what to look for when hiring contractors. They also include detailed cost breakdown tables and spreadsheets for estimating your own new home construction building costs.

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