What Is Backfill in Construction?

Backfill is a crucial part of the home construction process. Without proper backfilling procedures and materials, your foundation and home could suffer severe damage.

But what exactly is backfill, and why is it so important? This article explains everything you need to know about backfill, including the process and how it impacts your living environment.

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Backfill 101: What Is It?

During your home’s construction, contractors begin by digging the ground to lay the footings and foundation. Once the foundation and walls are in place, the gaps and holes left behind must be filled.

Backfill is any material you choose to occupy the holes around the foundation slab and walls. You can use the already dug-up soil, a mixture of gravel and sand, or other commercial refill products. The type of backfill you choose will depend on a variety of factors. Nevertheless, the process of filling the trench should come in layers. Once you build the floor joists above the foundation, fill the holes.

Here is what proper backfilling can do for your home:

Increases the substructure’s strength to support the load of the home or building above it
Supports your home’s foundation
Adds to the overall performance and stability of your home
Assists exterior water drainage

Types of Backfill

Backfill materials can vary. It all depends on the type of project you’re dealing with, as well as your drainage system. Your contractor may recommend and use one of the following types of backfill:

Coarse-grained Soil: A high-quality, easy-to-compact mixture of gravel, sandy soil, and fine materials that provides foundational support.
Limestone Screenings: A well-compacted material ideal for sewer and pipe backfills or as a base for brick paving.
CA7 Bedding Stone: A grayish, self-compacting material used for bedding pipes, subbase work, and to improve soil drainage.
CA6 Base Stone: A subbase granular backfill used in residential projects and for roadway shoulders.
Trench Backfill: Similar to CA6 base stone, this small aggregate drains and compacts well.
3” Coarse Stones: These have great drainage properties and are ideal for the first layer of backfill and filling large holes and trenches.
Commercial By-products: Ideal for when previously dug-up soil is not compatible with your needs.

Backfilling in 5 Steps

Builders backfill the holes around your foundation in five steps:

Clean the area intended for backfill and pump out any stagnating water.
Identifying the necessary backfill materials.
Pour backfill material into the holes in consecutive layers of around 20 cm, beginning from the corners.
Compact the layers between refills with a roller or other machine.
Further compact the layers with steel or wooden log rammers and water them.

The Importance of Compacting the Backfill

In reality, no matter how well builders backfill the soil around the foundation, it will remain somewhat loose and could cause problems down the line. One of the most common issues is heavy rain or melting snow absorption. Water will begin to push the walls of your foundation (crawl space or basement) in what’s called hydrostatic pressure.

If such a scenario occurs, hydrostatic pressure will create cracks and fractures in the lower level of your home. It can bow your walls and lead to water infiltration, paving the way for costly repairs. To avoid such damage, it’s important to backfill the foundation properly. Builders do this by using compaction equipment and rollers.

Worried About Backfill Issues? Contact Tar Heel Today!

Tar Heel Basement Systems inspector shaking hands with a homeowner

Backfill and associated foundation problems can be complex, but local foundation repair professionals are equipped to help you protect your home. Our Tar Heel Basement Systems team is here to help if you have questions about your foundation or the soil around it.

Contact us today to schedule a free inspection and repair quote. We’ll assess the situation and recommend further steps to keep your home free from leakage and other water-related issues.

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Holly Richards-Purpura

Content Writer

Holly is a Content Writer for Groundworks who has written and edited web content for the foundation services industry for almost 10 years. With a background in journalism, her passion for the written word runs deep. Holly lives in Columbus, OH, with her husband. Along with educating homeowners, she also has a big heart for the Big Apple.