Before you can start your basement conversion, sometimes underpinning a house is necessary.

Basement underpinning is a huge job that homeowners are rarely aware of. This reference guide will help you understand the basics of underpinning a house.

To better support a structure’s foundation, underpinning is required. When it comes to basement remodels, the most typical method is to extend the depth or distribute the weight of the property across a larger surface area. There are various options for underpinning a home, depending on the type of work that has to be done.

If you’re building a new basement or lowering the floor of an existing one, your home will need to be underpinned to either create the area from scratch or lower the ceiling.

Types of underpinning

There are four primary types of foundation: mass concrete and piled underpinning, jet grouting, and geo-polymer. Let’s explore each one.

Mass concrete

The most typical technique of underpinning a home is to dig out the soil beneath the foundation and then pour in the concrete. This method involves building a foundation underneath the current one, which is most often used for basement conversions.


Piled underpinning is when piles are driven into weak property foundations to stabilize them. The pin goes through the wall and is attached to the piles. This is usually done when the ground has wet soil that has built up over time.

Jet grouting

Jet grouting is a type of soil stabilisation that’s used to improve the ground or stabilize soil beneath a building’s foundations. We inject a stabilising fluid into the subsoil at high pressure and velocity. As a result, the ground solidifies and is stabilized in the same manner as cement.


Geopolymer injection is a relatively new process that involves injecting a geopolymeric resin into the ground to fill any underground voids. Geopolymer is much less disruptive as it only requires a few injection holes to be made.

Basement underpinning

A wall that can span unsupported for up to 1.2 meters is necessary to underpin a basement. The foundation for the new building may then be constructed directly below, with additional pieces of lower-level basement foundations and walls being laid out in sequence. The wall is supported along its entire length.

Ways to lower the existing basement

If there is already an underground structure on a property, it would need to be adapted to make it tall enough for people to use. Most basements are only crawl spaces, so if you want to turn yours into a liveable space, you’ll need to change the structure of your foundation first.

If you’re looking for a solution, underpinning is often the best answer. Another way to lower a basement’s floor level is by ‘benching’. This method is often quicker and less expensive. You’ll need to dig down to the depth of the floor level you want, and then build new walls extending from that depth up to the existing floor level. The new foundation floor is surrounded by a ‘cap’ on top, creating a structure that looks exactly like a bench.

The best solution for your space is determined by factors such as the soil condition, proximity to other homes, and the sewage system of the property. Furthermore, the project’s timeline and budget are essential considerations.

If you want to learn more about lowering your basement floor the right way, or if you have any other questions about adding a basement conversion to your property, reach out to G8Builds. We can help you develop a plan and construct a basement that will make you proud.

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