Sometimes a basement is a tiny crawl space and not useful for many reasons. When this is the case, homeowners often decide to lower their basement floor to make the area larger and deeper. Because of this, knowing how to lower a basement floor and the benefits of doing so is important.
There are two ways to lower a basement floor: underpinning and bench-footing. Underpinning involves digging beneath the footings and building additional concrete support underneath the foundation. Bench-footing is usually faster and more affordable and involves digging down and creating new, extended walls.
In this article, you will learn about the two different methods you can use to lower your basement floor, as well as things to keep in mind when doing so. Additionally, you will find information about the benefits of lowering the basement floor and how much you can expect to pay for the project.
Contents (Jump to Topic)
- Can You Make a Basement Deeper?
- Why Lower Basement Floor?
- Things to Consider Before Lowering Basement Floor
- Benching vs Underpinning
- How to Lower a Basement Floor
- How Much Does it Cost to Lower a Basement Floor?
- Can You Lower a Basement Floor Yourself?
- How Deep Can You Dig Out a Basement?
Can You Make a Basement Deeper?
It is possible to make an existing basement deeper by lowering the floor, but it has to be done correctly or the structural integrity of your home or foundation could be compromised. Many homeowners dislike their small basement and would love to have the extra height for many different uses.
However, just because you can deepen a basement, that doesn’t mean every homeowner should do it. There are other factors to consider, especially since it can be an expensive and time-consuming project.
Some elements like the type of soil, size of the house, the weight of the house, and the condition of the foundation can all influence the ability to lower the basement safely and effectively. You also have to make sure that you will not disturb any other elements of the structure or utilities and the floor will still have to make a water-proof seal.
For many people, lowering the basement floor has more benefits than downsides, but what are those benefits and why would you want to lower your basement?
Why Lower Basement Floor?
There are many reasons to lower a basement floor, depending on your current situation. Some of the reasons are best for those wishing to stay in the house for a while, but others may be good even if you plan on selling in the future.
One of the benefits of a properly lowered basement floor is the improvement in the house’s structural integrity. This is because the process to lower the basement floor will address some structural and stability problems like sagging beams, unstable walls, and poor footings.
Lowering the basement floor also gives you a chance to waterproof the area since basements are the most common area for water infiltration that can cause damage. During the process, you may also be able to fix some cracks and other problems that may cause moisture to make its way into the interior of your home.
After lowering the basement floor, there will be more vertical space to do as you please without bending over when moving around in the small area. This can also prevent you and your guests from bumping their heads on the ceiling when going into the basement.
The increase in space can be beneficial for a few different reasons. You can use it for ample storage as you accumulate more and more things throughout your life. It also gets seldom-used materials out of the way until you need to retrieve them. It is also possible to utilize the basement as a new living space like a game room, gym, playroom, theater, or even a bedroom.
Finally, lowering the basement floor will probably increase the value of your home. This is because of the other benefits and adds functionality and space to potential buyers. Most homebuyers are interested in having a lot of space, whether for hobbies, storage, or something else and having a high basement ceiling can make your home more attractive.
Things to Consider Before Lowering Basement Floor
Before you decide whether you want to lower the basement floor, there are some factors to keep in mind. First, you need to consider your budget and how long you plan on being in the home. If you are moving soon, you have to ask yourself if the increase in property value is worth the time and finances required to lower the basement. It is an expensive project and can go beyond your budget.
You also need to examine why you want to lower the basement floor and if that will be possible within your home’s capabilities and your budget. If you are going to convert it into a living area, then you will also need to make sure that it has outlets, air conditioning or heating, windows, fans, and other things necessary for comfort.
There are other considerations regarding the floor itself and the foundation and walls around it. If the foundation is in poor condition, you may not be able to lower the basement safely without first addressing the structural issues within the foundation. This is because a damaged or shifted foundation may not handle the stress and changes that are essential for lowering a basement floor.
Benching vs Underpinning
Benching and underpinning are the two distinct methods for lowering a basement floor and knowing the characteristics of each one can be crucial for determining what is right for you and your home. Both options will add space without compromising the sturdiness of the basement, but there are major differences as well.
Foundation underpinning allows you to strengthen the foundations of your home while simultaneously creating ample space. This method involves digging holes beneath the foundation footing, which is the portion of the foundation that supports and transfers the load to a larger area. Underpinning is a slow and methodical process that can take time and cost a lot of money.
In addition to strengthening the structural integrity of your house, underpinning can also provide other beneficial properties. By lowering the floor, the headroom is increased and allows you to install lighting fixtures or ceiling fans and windows or doors in the basement area. It also gives you the opportunity to take care of any repairs in the house’s plumbing, electrical, or insulation components.
These great benefits are balanced with some downsides to underpinning as well. The main problem that homeowners have with underpinning is the scope of the project itself. It requires substantial resources and experienced professionals in most cases. Also, city inspectors will usually require a structural engineer to inspect the changes after you finish lowering the basement floor. Because of all this, underpinning can be incredibly expensive.
In contrast, foundation benching is a more affordable and faster way to engage more space in the basement. Benching is characterized by creating new walls to extend from the new depth up to the original, existing floor level. The new wall has to be reinforced and will take up some of the space in the basement, but the walls can be used for cabinets or shelves that can give you some of the space back.
Benching is less time-consuming than underpinning and is also more affordable. Benching does not demand as much labor and does not involve any changes to the foundation walls. The benching process can also be used to add decor like shelves or cabinets and can even be used as a chair.
Those are some great benefits, but there are also disadvantages as with anything. The aspect of a basement benching project that is complained about the most is the reduction in square footage in your existing basement. It is also less likely to boost property value as much as underpinning and the benching process does not require or encourage foundation repairs.
How to Lower a Basement Floor
Now that you know about the two ways to lower your basement floor, it is important to look at how those projects are completed, whether you are planning on doing it yourself or hiring a professional.
Before looking at how to proceed with underpinning and how to use underpinning to effectively lower your basement floor, it is important to note that you should never make any structural changes to your home without speaking with a structural engineer or other professional. It is also a good idea to talk to your home insurance company before beginning the project.
What you will need:
- Professional Engineer Drawings
- Concrete Vibrator
- Non-Shrink Grout (Optional)
- Wood ( 2x4s and ¾ inch plywood work well for forms)
After receiving professional drawings to identify and designate sections around 3 to 4 feet in length around the perimeter of the basement’s walls. In addition, these sections will be numbered for the order to work on them. Once an engineer has provided those sections, you need to excavate them. There should be 6 to 8 feet of in-tact foundation between each 3 to 4-foot portion that you will dig out.
Start with only the sections marked with a 1 and dig down enough to hit undisturbed soil. You will also have to dig back 18 to 24 inches to ensure that the footing will extend underneath the entirety of the foundation.
You will need to build forms out of wood to ensure the footings are shaped correctly and are supportive and centered. The 2x4s and plywood should go around the edges of the excavated area and ensure that the concrete dries sturdy and properly. You also have to make sure that the concrete will fill in the areas necessary for the structural support of the existing foundation.
The next step is to pour the concrete and ensure that it flows underneath the existing foundation to add support. You can do this in a few different ways. You can do it flush with the existing structural components or step out slightly away. The over-pour method will make the forms flush with the height of the existing footing and the step method allows for a 2-inch space filled with non-shrink grout. An engineer can also help you determine the best method for your basement.
Once you pour the concrete, you will have to use a concrete vibrator to eliminate air bubbles and pockets, distribute the concrete evenly, and ensure that the concrete will be structurally sound.
Steps 1-3 will be repeated for the sections marked 2, then 3, and so on. Make sure you allow the previous sections to completely dry and form properly before moving to the next portions.
After you have all the footings providing support around the length of the foundation, you can excavate the remaining dirt and soil down to the depth of the new footings you created. After doing this, you can work on waterproofing, gravel, weeping tile, plumping updates, etc. Finally, you can pour the new floor of the basement.
Bench footing is more DIY-friendly, but it is still best to consult with a structural engineer before doing any major project related to the foundation. This method also leaves the load-bearing soil under the existing foundation footings and keeps it encased in concrete.
What you Need:
- Wood (2x4s and ¾ inch plywood work well for forms)
The first thing you will have to do when bench footing to lower a basement floor is to dig down to the depth you desire for the new, lower floor. You should be able to see where the foundation ends and the load-bearing soil begins. This is where you need to create a new wall or a “bench,” to ensure that the soil remains in place underneath the foundation while reinforcing a new area down to the lowered basement floor.
When digging, be sure to keep an angle from the foundation to the bottom of the depth. This allows the bench to meet down in a slope from the foundation to the new flooring. You never want a decline that is too steep because it will not be as structurally supportive, but one that is too wide will take up much more basement area.
After you know where the bench must exist for proper footing, it is time to build the forms and reinforcement using rebar. The rebar should be placed all around every foot or so to make sure that the concrete will be sturdy and durable. It should bend to keep the concrete strong throughout.
As far as the forms go, you want them to shape the concrete, but the depth partially determines the width. The deeper you go, the wider the bench will have to be. Remember that the larger the bench, the more basement room it will consume. The forms can be made with 2x4s for the frame and plywood to keep the bench flush against the forms, foundation, and load-bearing soil.
Once the forms are in place and the rebar is placed at regular intervals around the perimeter, it is time to pour the concrete. You want to pour the concrete so that it piles up slowly and gradually to ensure no slips in the forms occur and make sure that there are no air pockets or other factors that can weaken the integrity of the bench footings. Once you are done, you can do final touches like waterproofing, weeping tile, plumbing, and the installation of the new floor.
How Much Does it Cost to Lower a Basement Floor?
The amount that it costs to lower a basement floor can vary greatly from one project to the next depending on the condition of the current foundation, the soil type, plumbing, and other factors. However, it generally costs anywhere between $20,000 to $50,000 for underpinning, with each square linear foot costing $300 to $500.
If you want to calculate the cost of underpinning or bench footing for the entire area of the basement, then you can calculate it with avenges. You can expect to pay somewhere between $75 and $100 per square foot for underpinning. Benching is significantly more affordable at around $25 per square foot.
Can You Lower a Basement Floor Yourself?
Other than the fact that you will need guidance from a structural engineer and it is a huge project for one person, if you have help and consult with a professional, it is possible to lower your basement floor yourself. However, if you are using the underpinning approach, just know that it takes a lot of time and is a fairly difficult project.
Benching is more DIY-friendly but can still be hard to master if you have never done it before. You will still need advice from a structural engineer and solid planning to make the project go smoothly. Using the bench footing method to lower your basement yourself is certainly possible as long as you know what you are doing.
Just know that you are messing with the structural support components of the home and a mistake could be disastrous and expensive. Because of this, most homeowners rely on foundation companies or contractors to do the work.
How Deep Can You Dig Out a Basement?
While it can depend on the type of soil and other factors, most safety guidelines recommend a basement no deeper than a single floor or about 8 to 10 feet. Any depth over this limit and you could come across safety hazards and compromise the strength or placement of the original foundation. If you have a basement lowering project in mind but are unsure about the depth, it is best to speak with a structural engineer or another experienced professional to make sure that it is okay to dig deeper.
Lowering a basement floor is usually possible and there are two primary ways of doing it. Underpinning involves adding footing underneath the foundation and bench footing utilizes an extension out and down away from the foundation. There are a lot of benefits to lowering your basement flooring. Just make sure that you take the necessary precautions and plan ahead and you may find that you can make your basement more useful than ever before.