Can you Convert a Crawl Space into a Basement?

If your house has a crawl space under the floor, converting it to a basement can seem like an easy way to add some much-needed space to your home. Just dig down a little, shore up the posts a little, and you have a new room for your house. But, is that really something you can do?

Can you convert a crawl space into a basement? Yes, it is possible to convert a crawl space into a basement. It is not a DIY project, however. Converting a crawl space to a basement is a massive undertaking that requires professional help. It requires a tremendous amount of labor and professional engineering knowledge.

Why do you need a professional? Because you must temporarily support and extend the foundations of the house as you are digging down. If you damage the foundation, your home could collapse. You must also install concrete walls and foundations around the outside of the basement. Don’t try to do this yourself – hire a pro.

This project is not simple, easy, or cheap.

What’s Involved in the Conversion?

To convert a crawlspace to a basement, follow these steps:

1. Mark out the boundaries of the new basement
2. Shore up any foundation piers that are in the basement
3. Dig soil out of the basement 
4. Pour a new concrete retaining wall around the edge of the basement
5. Install a drainage system in the floor
6. Pour a concrete slab for the basement floor
7. Add stairs and lighting
8. (optional) Finish the basement for use

Let’s look at each of these steps in more detail to understand why this conversion is so expensive.

Mark Out the Boundaries

This is something you can do yourself. You decide how big the basement should be. If you get it wrong in some way, your expert can tell you. However, if you are footing the bill for the project, you should decide how big you want your new basement to be. You can use stakes and string or spray paint to mark the boundaries. Once it’s marked out, you need to step back and let the pros take over.

Bigger is better here – the engineering work will cost the same for a big basement or a small one. Getting extra concrete poured won’t add much cost. Material removal will be more expensive, but not all that much. And once your basement has been finished, you don’t get a second chance to expand it. It’s best to make the basement as big as you can on the first pass.

Shore Up Foundation Piers

The next obstacle you have to face is the foundation piers that are in the basement area. Homes with crawlspaces are called pier-and-beam construction. Your house has several concrete piers that hold it up off the ground. These piers are resting on soil. As you dig away the soil, the piers will become unsupported. You must temporarily support the foundation and block under the columns as the ground goes deeper.

Keeping the piers shored up is one of the jobs that require a professional. The final piers will need to be engineered to support your house once the basement is complete.  Your local building inspectors will have to okay the engineering and the supports once they are finished.

A word of advice:

“Professional engineer” is a legal term for someone who has passed rigorous tests and earned experience in the real world. It has legal ramifications, and you almost certainly will be required to have a professional engineer design your new basement setup.

Dig Out the Basement

Digging out the basement is part of the reason why the project is so expensive. You have to dig out the basement to a depth of ten feet. If you want a basement that is twenty feet square, that works out to 4,000 cubic feet of dirt to move.  This is about fifteen dump truck loads. Depending on your soil type, 4,000 cubic feet can weigh anywhere from 284,000 to 624,000 pounds. That’s a lot of dirt for a small basement.

Fifteen dump truck loads are a full day’s work for a backhoe operator. But, since a backhoe will not fit into a basement, it has to be dug by hand using a shovel. A big part of the cost of a crawlspace conversion is the fact that someone has to go into the crawlspace with a shovel and move thousands of cubic feet fo soil by hand.

If you are looking to save money on the project, you might be able to save some here. If you are physically capable and have the time to spare, you can probably do this yourself. Just make sure you shore up your foundation as you dig.

Pour a New Concrete Retaining Wall 

If your crawlspace was dug out to begin with, it probably has a concrete wall around the edge to help it keep its shape. If you don’t have the wall to start with, you’ll need one when the job is done. The retaining wall keeps the soil around the edges from collapsing.  It also helps support your house.

A professional engineer must design a retaining wall like this. Between the complexities of soil and the load of the house, it takes serious know-how to get the wall right. It also requires an expert to pour and finish the wall correctly.

Install a Drainage System

Once your basement is dug, and you’ve made sure the house will stay on top of it, you need a drainage system. A ten-foot hole is an excellent place for water to pool up, especially after a hard rain. You need a proper drainage system to keep that from happening. Building a system to get water out of a ten-foot hole is also a job for an expert.

Pour a Concrete Slab for the Floor

Another task, another reason to call a pro. Concrete work is deceptively tricky. Pros make finishing concrete look easy, but it’s tough to get a smooth, attractive finish. You’ll want someone skilled to handle this so that your floor doesn’t look like a kid’s mud pie.

Add Stairs and Lighting

You will need stairs to get into your basement and lights to see what you are doing. You might be able to do these yourself. Stairs take basic carpentry skills, and lights and outlets are one of the easiest electrical projects. If you aren’t handy or don’t know your way around a breaker box, these will also need to be hired out.

Finish the Basement for Use

If you want storage space, you can skip this step. Boxes pile up as well in a bare concrete room as in a pretty one. On the other hand, if you want to have an attractive space to use, you’ll need to add sheetrock, flooring, and paint.

Bottom Line

It’s easy to see why converting a crawlspace to a basement is so expensive. There is a colossal amount of unskilled labor, professional engineering time, and skilled trades work that goes into it. This isn’t a job you can muddle through on the weekends. It will take a long time and cost a lot of money.

If you need space, you can convert a crawlspace into a basement. However, there is probably a more straightforward and cheaper way to increase the size of your house. Attic conversions, garage conversions, additional rooms, even a new story on top would probably be less expensive than a crawlspace conversion.