How to Turn Your Crawlspace Into a Basement (and When You Shouldn’t)

Space is a big motivator when it comes to buying a house; sometimes it seems as if people start planning to buy a bigger house the moment they move into their current one. And yet, after years of growth, new houses have actually been getting smaller over the last few years, dropping from a median of 2,519 square feet in 2015 to just 2,191 last year.

The rule of thumb on square footage is that you need about 600 to 700 square feet per person living in a house, so if you’re a family of four you ideally want about 2,400-2,800 square feet. And adding square footage can pay off—every 1,000 square feet of additional space in your home can potentially boost your home’s value by 30%. There are several options for adding square footage to your home, but most depend on having space to expand into. If you lack outdoor space, can’t build up due to zoning laws or other barriers, and you have a shallow crawl space that’s not usable for any activity except crawling, you might ask yourself if you can solve your square footage problem by going down.

Can you? Possibly. Should you? That’s a more complicated question.

Digging out

Digging out a crawl space or shallow basement is just what it sounds like: You dig, removing the dirt and other debris currently forming the floor, lowering the floor until you have usable clearance above your head. It’s more complicated than that, of course: You also have to extend and reinforce the foundation and footings via underpinning or buttressing, and you have to figure out how to remove all that dirt.

There are many considerations involved when deciding whether it’s possible to dig out your crawl space:

Soil. The type and condition of the soil your house is built on is a big factor. Loose, sandy soil is more likely to collapse during the process.
Age. Homes built before the 1950s rarely have foundations made from reinforced concrete, and tend to have thinner footings, making a dig out much more difficult.
Foundation. The type of foundation matters, too; older foundations made from bricks are less stable, especially if the mortar is sandy. Monolithic concrete foundations are better for dig outs.

If you consult with a structural engineer and decide it’s possible to dig out your crawl space and get that valuable square footage added to your house, you still have to decide if it’s worth it. And it very well may not be.

Considerations

There are a lot of potentially disastrous downsides to digging out your crawl space to create a basement you can then finish:

Cost: The total cost to dig out a crawl space and create a finished basement can be as much as $200,000. Even if you get that 30% bump in your home’s sale price, it’s going to be tough to get a solid ROI on that.
Risk: Homes can—and do—collapse when crawl spaces are dug out. Even when proceeding with extreme caution, digging out can weaken the foundation and cause it to shift, which can set off a chain reaction of failure that leaves you not only with no new basement, but also no house.
Cost, again: Because of that extra risk, you’d be well advised to buy extra insurance if you undertake the project—especially because catastrophic failure of your home’s stability can impact your neighbors on every side. You’d better be prepared for that kind of liability.
Time: This isn’t a quick job. It can take weeks to dig out a crawl space, and you may not be able to stay in the home during the process.

Bottom line

You’ve got a crawl space you try your best to never enter. You’re dreaming of a finished basement or accessory dwelling unit. Should you dig out your crawl space? Only if you answer “yes” to the following questions: