Cost of Lowering a Basement Floor

Written by: Staff

Lowering a basement floor, often referred to as underpinning in the contractor world, is a process of digging out the existing basement floor and simply lowering it a foot or so.

This process, as you can imagine, can create more space, making it more usable and even adding value to your home.

Cost of Lowering a Basement Floor
VFW Basement Flooring – Epoxy Vinyl Chip” (CC BY 2.0) by Decorative Concrete Kingdom

Lowering a basement floor costs

The costs to lower a basement floor can greatly vary as there are so many variables involved, including your geographical location, the contractor you choose, the size of your job, the complexity of the work, the pipes beneath the flooring that needs to be removed, how the floor is going to be lowered, your home’s condition and so much more.  With so many variables, again, it will be so hard to offer an exact estimate, but for a conservative estimate, based on the estimates we read online, you should be prepared to spend anywhere from $10,000 for a very basic job to as much as $60,000+ for a complex job.  Contractors warn you should be prepared so spend at least 10-20% on the engineering costs alone.

In a very detailed answer on Angie’s List, a member named LCD said you should be prepared to receive a larger range of quotes ranging from $9,000 for a bare bones job to as much as $40,000 for a job where everything is going against you.

One member on this forum thread said he was getting quotes for about $20,000, but the costs, like we mentioned, would depend on the linear feet, to lower his basement for his home built in 1921.  On this same thread, another member chimed in and stated she paid close to $40,000 for a 982 square foot home in order to add eight feet ceilings.  This quote included the dig, concrete floor plus some reinforced footings.

On a thread, a member said his company did this job many times and the costs were about $15,000.

Steve and Rachel at did a great job taking photos of their basement as it was being dug out by a contractor.  According to the top comment, someone asked her what the job had cost, and she had said it cost about $6,000 to break up the concrete, dig about 10 inches and pour in new concrete.  This didn’t include any plumbing components, lowering drains and/or moving lines.

The extra costs to think about

Demolition – This is a big one as contractors will have to use tools by hand to dig, break up concrete and bring in new gravel.  Being a labor-intensive job, the larger the job, the more you’re going to have to pay the crew.  The same can be said about the depth desired or type of soil.  If, for instance, dewatering is needed to soften the soil, then the time can increase, while bedrock, if present, could increase the costs by more than 50-75%.

Interior Finishing – Of course, these estimates are for lowering the floor only, and when the job is complete, you will be left with a bare-bones basement with a new concrete floor.  Be sure to factor in any interior finishes you need such as doors, flooring, paint, drywall and framing, to name a few.

Plumbing – Will any of the new areas require any sort of plumbing?  If you want a new bathroom installed in the basement, then the plumbing will need to be considered before the new concrete flooring can be used.

The condition of the walls – Deteriorated walls can affect your plan as these walls may not work as well when the new foundation is being poured, meaning the contractor will have to perform the job in smaller pieces.

Lowering a basement floor process

The first steps start with an architect or engineer, a professional who is going to draw up a blueprint, based on your specifications, for your contractor.  This paperwork will also be sent to your local zoning department for approval and based on their response, it will either be approved or the inspector may ask for changes before they give you permission to start.

Once your local zoning department issues a permit, the contractor will start by either creating a bench to help support the dirt underneath the foundation or directly removing the soil beneath the foundation wall while replacing it with concrete.  Also, depending on the elevation and your setup, at this time, the drains may have to be re-adjusted in order for the water to escape your home as the concrete is being poured.  At this time, all of the existing concrete will be removed, often broken up with jackhammers.

As this is being done, the foundation footings will start to expose, and as it does, small sections of soil around these footings will be dug out and a new concrete foundation will be poured to help support the home.

When the extended foundation walls are installed, an additional wall of concrete, referred to as a knee wall, will be poured around the perimeter, overlapping the footings to add even more support and strength.

Next, the interior of the home will be waterproofed and drain tile is often installed to help prevent any future seepage.  A dewatering channel, often installed on the newly created bench ledge, will also be installed to help capture any seepage that may come through the original foundation.

Lastly, a layer of gravel is poured, leveled and is covered by a vapor barrier and reinforcing grid, readying it for the newly poured concrete floor.

With so many factors, the time to complete this job will greatly depend on the size of your basement.  A small basement with no obstacles and very little repairs/modifications can take as little as a week, while a complex, larger-than-average sized basement with many unforeseen problems could take more than four to six weeks to complete.

Tips to know

Before getting excited about lowering your basement floor, you will first want to check with your zoning and planning department to make sure you’re even allowed to do this.  Even if allowed, you may be limited as to how much you can lower your floor.

A good contractor should always have a connection with a reputable civil engineer who is able to assess your structural and foundation situation before the contractor even thinks about starting the job.  Since the contractor will dig down deeper, the soil supporting the footer of your foundation may cause the house to fall down or do extreme damage, which could cost you tens of thousands of dollars, if the contractor doesn’t know what he or she is doing.  Typically, a contractor will remove the soil in small strips and lay concrete as beams across the basement floor to tie into the home’s foundation footers.  This is done to prevent the footers from kicking in and causing the damage as mentioned.

Do not plan on recouping much of your costs when thinking about the resale value as many real estate agents note you will only see about a 30-40% increase in value.

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