Can You Add A Basement To A House On A Slab?

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Making a basement is a great idea to create space in your home. But first, you have to assess the structure of your house. A house on a slab lacks enough crawlspace. With limited space, adding a basement is tough. That is why we have consulted with the experts regarding whether you can add a basement on houses built on a slab, and here's what they have to say.

Yes, you can add a basement to a house on a slab. But it would not be possible in some states due to the soil type and frequent rainfall. There are varying requirements of state building codes that you have to follow. Aside from the legal and technical elements, you also have to account for the costs. The project will not be cheap because of these underlying processes:

  • Pouring the foundation
  • Drainage installation
  • Electrical and plumbing work
  • Flooring and wall preparation
  • Other finishing processes

With the costs and processes of adding the basement, you can proceed if you are totally confident in moving forward with the project. But any mistake will damage your home. So make the safety and comfort of your family your top priority when building the basement. If you are ready, read further to learn how you can add a basement.

A concrete slab preparation for a house renovation, Can You Add A Basement To A House On A Slab?

Can You Dig Under A Concrete Slab?

Yes, you can dig under a concrete slab. However, even if digging is possible on your own, it is best to hire professionals to excavate the ground to prevent any damage to the existing house foundation. Keeping the foundation's strength prevents your house from sagging.

As a precaution, you have to check if the area is feasible for digging. Also, make sure that the area is dry if you are digging in a flood-prone area. If the house has insurance, ask your insurance provider to clarify the provisions.

You will need heavy equipment like a skid steer to dig up the soil from under the ground. In urban areas, contractors dig down by hand.

You also have to account for the time needed to complete the project. It will take around 3 days to 3 weeks for digging, but it could take even longer. The time varies due to the available equipment and the desired basement size.

Concrete slab for a new home

Can You Install A Basement After The House Is Built?

You can install a basement under an existing house. It might seem impossible, but more homeowners are embracing this idea. Remember that you also have to abide by your respective state building codes. Some provisions include the limitations for excavation and ceiling height requirements.

Read more about basement ceiling height requirements: What Is The Minimum Height For A Basement Ceiling?

Here are two ways to install a basement after building the house:

1. Lifting The House

The safest and effective way to install a basement below an existing house is by lifting the house. There would be enough space to dig and excavate the soil. Professional house moving firms reinforce and add braces to the house, then lift it with a crane. Afterward, you can proceed with the excavation.

2. Underpinning

Underpinning is another common process involved in creating spaces underneath an existing building. By underpinning, contractors increase the depth of the foundation. The process involves the sequential excavation and pouring of concrete on the underside to reach the desired depth.

The two types of reinforcing new foundations with underpinning include:

  • Mass concrete underpins - There are no steel reinforcements on the new foundation.
  • Reinforced concrete underpins - There are steel underpins to support the structure.

Read more about adding a basement under an existing house from our previous post: Can You Build A Basement Under An Existing House?

How Much Does It Cost To Build A 1,000 Square Foot Basement?

If you plan to build a basement, you have to consider all related costs. Like most home improvement projects, the cost can be a deal-breaker.

You might end up buying sub-standard materials for the basement if you do not have enough money in your budget. From preparation to finishing, every step incurs costs.

For a 1,000 square foot basement, you might spend around $30,000 to $45,000. Listed below are the usual costs you can incur when building a basement:

  • Cost of digging - $10,000 to $30,000 (includes disposal)
  • Plumbing and drainage work - $3,000 to $10,000
  • Pouring of the concrete foundation - $10,000 to $30,000

But your spending does not stop there. You have yet to finish the basement. The basement finishing will vary depending on the style and functions you want to install. You will have to pay about $30,000 for the following:

  • Framing of walls
  • Flooring
  • Electrical wiring and water connections
  • Drywall
  • Painting
  • Waterproofing

The materials for each component of the basement must also be of good quality. You will spend more if the fixtures deteriorate after a few months or years. Invest in durable and long-lasting materials to avoid frequent repairs or replacements.

In What Order Should I Finish My Basement?

Staircase to basement room with a brightly lit window. Are Basement Apartments Cold Are They Cooler In Summer

After excavating and creating a structure below the ground, your final process is to finish the basement. It would take you around 4 to 8 weeks to complete the basement. But the time might extend if the basement area to finish is big. Before finishing, you have to prepare the basement first.

Preparing The Basement

An unfinished basement with wooden framing for the partition and unplastered walls

Before you finish the basement, you have to prepare legal documents. It is best to apply for a permit, even though it is optional. If you plan to sell the property in the future, you will not encounter any problems. The permit costs around $400 to $1,800, depending on the project size.

You also have to plan for the type of ceiling, walls, and other fixtures you want to see in your finished basement. You should also be able to choose suitable materials and tools for finishing. Some crucial basement finishes include the insulation, paint colors, and type of flooring.

It is also important to plan for the safety features of the basement.

Lastly, you have to prepare the basement surface. Get rid of the dampness in the area by using a dehumidifier. Check if there was recent flooding in the unfinished basement. You have to make the area dry and repair all possible cracks where water can flow.

Finishing The Basement

After the planning and preparation, you can follow these steps to finish your basement:

  1. Cover the walls and ceiling of the basement with insulation. Fill the gaps with caulk or similar sealants.
  2. Frame the basement walls. You can ask a professional in the step.
  3. Install the plumbing, electrical, and air connections before closing the frame of the wall.
  4. Close the frames with drywall.
  5. For the ceiling, it is up to you if you want to leave it exposed or not. You could paint the exposed connections or cover them with drywall.
  6. Before painting, smoothen out the areas with sandpaper.
  7. Prime the walls and ceiling. Then add two coats of paint. You can use soundproofing paint if you have plans to reduce noise in the basement.
  8. Get down with the flooring. Use your choice of flooring, along with some waterproofing methods.
  9. Attach the doors and trimmings.
  10. Add furniture and storage to complete your basement.

In Closing

You can add a basement to a house even with a limited area. Take note that the processes are costly and exhaustive. You will need to dig out from the ground below to create your basement. Even with an existing house, you can still create a basement by lifting the house or underpinning.

The process from preparation to finishing a new basement is costly. In every step of constructing the basement, you incur costs. It is always best to plan to avoid more expenses for repairs or replacements in the future. Always ask for professional help to achieve a successful basement project.

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