What does a “slab” basement mean in a real estate context?

In real estate, a “slab” home does not actually have a basement. It sits on a slab-on-grade foundation, a single layer of concrete poured directly on the ground, so there is no below-grade space to walk into and no crawl space under the floor. When a listing says “slab,” read it as no basement and no crawl space. The house rests on a flat concrete pad.

That word trips up a lot of New England buyers. Around here most homes have a full basement, so “slab” stands out. It is common in newer builds and in additions, less common in older NH housing stock.

What a slab foundation actually is

A slab is one poured pad of concrete, usually a few inches thick, with thickened edges (footings) where the walls sit. The plumbing and sometimes the heating lines run inside or under that pad before it is poured. There is no hollow space underneath. The finished floor of the house is right on top of the slab.

Compare that to the two other foundation types you will see in listings. A full basement gives you an eight-foot or so below-grade room. A crawl space gives you a short access area, often three or four feet, under the floor joists. A slab gives you neither.

Why the foundation type matters when you buy

The foundation shapes what can go wrong and what it costs to fix. With a slab, your utilities are buried in the concrete, so a plumbing leak under the pad is harder to reach. With a basement, you get storage and mechanical space, but you also get the thing we see every day in NH: water.

Here is the part most buyers miss. A slab can still have a basement somewhere else in the picture. Some homes are part slab, part basement, especially after an addition. So read the inspection, not just the listing word.

If the home you are buying does have a basement or a crawl space, that is where our work starts. We do not pour new slabs or build new foundations. We repair and dry the ones you already have.

The water and structure issues we see when there is a basement

Water pools against a foundation because the soil right around the house is disturbed backfill. That is the looser dirt that got put back when the house was built. It drains slowly and holds water. Add NH frost heave, and the freeze-thaw cycle can push walls inward over the years.

When water gets in, our fix is interior drainage. The Forever Dry System is full-perimeter interior drainage plus a sump pump (1/2 hp per 120 feet of drain), a 12-mil wall vapor barrier, and a dehumidifier. It is 100% guaranteed to be dry for life, transferable under conditions. Basement waterproofing runs $3,000 to $30,000. We do not do exterior excavation waterproofing. In our field experience it fails in about two or three years. Interior drainage is the durable fix.

If the home has a crawl space instead, that gets crawlspace encapsulation, which is a different system. A 12-mil wall and 20-mil floor vapor barrier, dimpled drainage matting under the floor, sealed seams, a dehumidifier, and a sump. Encapsulation runs $3,000 to $25,000. The DOE notes that up to about a third of a home’s heat loss can come from an uninsulated foundation or crawl, so this is comfort and energy, not just dryness.

Cracks, bowing walls, or settling are structural. Crack injection runs $1,000 to $3,000. Carbon-fiber straps for bowing walls run $850 each. If the house is settling, helical piers run $2,700 per pier for the first three, then $2,200 per pier after that. You may not need any of this yet. A free inspection tells you which, if any, applies.

A quick NH framing

A slab home means no waterproofing or finishing work is even possible below grade, because there is nothing below grade. If you want that space, a slab does not give it to you. A basement home gives you the room, and our job is keeping it dry and standing. Either way, know what you are buying before you sign.

For radon, slab homes still need testing. Radon can come up through any concrete pad. The EPA action level is 4.0 pCi/L, and the EPA suggests considering a fix between 2 and 4. We install active sub-slab radon mitigation systems, and that runs $900 to $6,000, and most homes land around $1,950 to $2,250.

Talk to us before you buy or after you close

If you are looking at a home with a basement or crawl space and you want to know what it will take to keep it dry and solid, call us at 603-610-1770 or book your free inspection. Free inspection, free estimate, quote within 24 hours. We serve New Hampshire, Maine, and Massachusetts.

Explore our basement waterproofing, crawl space services, structural and foundation repair, radon mitigation, and the 603 guarantee.

Related questions

Does a slab house have a crawl space? No. A true slab-on-grade home has neither a basement nor a crawl space. The floor sits right on the concrete pad. If there is any below-floor access, it is not a pure slab, so check the inspection report.

Can you waterproof a slab basement? A slab home has no basement to waterproof. If part of the home has an actual basement or crawl space, yes, we dry those with interior drainage ($3,000 to 30, 000)or[encapsulation](/crawl − space − services/)(3,000 to $25,000).

Is a slab foundation worse than a basement? Neither is worse. A slab gives no extra space and buries utilities in concrete. A basement gives you room but can take on water in NH. Pick based on what you want and what the inspection shows.

Do slab homes need radon mitigation? Sometimes. Radon comes up through any concrete pad, so test first. The EPA action level is 4.0 pCi/L. If it is high, sub-slab mitigation runs $900 to $6,000, and most homes land around $1,950 to $2,250.