What is the difference between a crawl space and a basement?

A basement is a full-height foundation level you can stand up and walk around in. A crawl space is a short foundation level, usually two to four feet tall, that you can only crawl through. Both sit under your house and both can let in water, soil gas, and damp air, but the fix is different for each, and so is the price. Basement waterproofing here runs $3,000 to $30,000, and crawl space encapsulation runs $3,000 to $25,000.

The short version

Height is the first tell. Finished or finishable ceiling height means a basement. If you have to duck or crawl, it’s a crawl space.

The floor is the second tell. Basements usually have a poured concrete slab. Crawl spaces often have a dirt or gravel floor, sometimes a thin rough slab. That bare dirt matters. It breathes moisture straight up into your house all year, and the job to keep each space dry is where the real difference shows.

Why both get wet

When your house was built, the crew dug a hole, set the foundation, then shoved the dirt back in. That refilled dirt is looser than the packed ground, so it drains slow and holds water against your wall. Building scientists call it disturbed backfill, and it’s why water pools at the foundation instead of running off.

Up here, frost makes it worse. NH winters freeze that wet backfill, and the freezing soil pushes against the wall and tries to bow it inward. Water finds the weak spots. In a basement that’s often the floor wall joint, where the slab meets the wall. In a crawl space it’s the wall, seams, or open dirt.

How we keep a basement dry

For a basement we install the Forever Dry System: a full perimeter interior drain, a sump pump sized for the run, a 12-mil vapor barrier up the walls, and a dehumidifier. It catches water at the floor wall joint and moves it to the sump before it reaches your floor. It is 100% guaranteed dry for life!

We don’t dig up your yard to waterproof the outside. We’ve watched exterior excavation jobs fail in about two to three years, so the interior drain is the durable fix. The Forever Dry System is a basement system and does not go in a crawl space.

How we seal a crawl space

A crawl space gets crawl space encapsulation instead, a different problem with different parts. We lay a 20-mil vapor barrier across the floor, run a 12-mil vapor barrier up the walls, and put dimpled drainage matting under the floor barrier. We spray-foam the seams so the space is sealed off from dirt and outside air. Then a dehumidifier and a sump keep it dry.

The goal is to stop the ground from breathing moisture into your home. The U.S. Department of Energy notes that up to about a third of a home’s heat loss can come from an uninsulated foundation or crawl space, so sealing it off can help the whole house feel less damp.

You don’t always need the full system on day one. If your crawl is bone dry with a clean slab, we’ll tell you. We won’t sell you a sump you don’t need.

Radon shows up in both

Radon doesn’t care which one you have. It’s a soil gas, and the EPA sets the action level at 4.0 pCi/L, with a recommendation to consider fixing between 2 and 4. New Hampshire has plenty of radon-prone ground, so NH DHHS pushes testing.

In a basement we run an active sub-slab system. In a dirt or fieldstone crawl we run a sub-membrane system that pulls the gas from under the encapsulation barrier. We install both. Radon mitigation runs $900 to $6,000, most homes land around $1,950 to $2,250, and a test is $50, credited toward the job if you move ahead.

What drives the cost difference

Size, water volume, and how much support work the structure needs. A bigger footprint means more drain, more barrier, and more labor. A wet space needs a sump and dehumidifier, and sagging framing might also need floor support. Crack repair, carbon-fiber straps, and piers are foundation work, not waterproofing, and we price those separately.

Get a real answer for your house

Call us at 603-610-1770 or book your free inspection. We’ll tell you whether you’ve got a basement or a crawl space, what’s driving the moisture, and what it costs. You get a quote within 24 hours, and it’s all backed by the 603 guarantee.

Explore the work: basement waterproofing, crawl space services, structural and foundation repair, radon mitigation, and basement finishing.

Related questions

Can a crawl space be turned into a basement? Not by us, and rarely worth it. Lowering a crawl into a full basement means underpinning the foundation and excavating, which is a major rebuild. For most NH homes, encapsulating the crawl gives you a dry, sealed space for far less. We price structural work after we see it.

Is encapsulation the same as waterproofing? No. Waterproofing manages liquid water with a drain and sump, which is what a basement needs. Encapsulation seals a crawl space off from ground moisture and air with vapor barriers. A wet crawl gets both, since we add a sump under the barrier.

Does a crawl space need a dehumidifier? Usually yes, once it’s sealed. The barrier stops new moisture from the dirt, and the dehumidifier handles the damp air already trapped down there. A sealed crawl with no dehumidifier can still grow musty. Ours carry a 5-year warranty.

Which one is cheaper to keep dry? It depends on size and water, not just the name. A small dry crawl can cost less than a wet full basement, and a large crawl with framing problems can cost more. Encapsulation runs $3,000 to $25,000 and basement waterproofing runs $3,000 to $30,000. We give you the real number after a free look.