Foundations
House foundation types: slab, crawl space, basement and pier and beam
Short answer
There are four main types of foundations a house can sit on: a slab, a crawl space, a basement, or piers and beams. Each one comes with its own typical problems, so it’s good to know which type you have and where to start looking if something seems off. A house can have more than one, especially if it has additions.
On this page
House foundation types at a glance
| Type | What it is | Typical problems | Clues you can see |
|---|---|---|---|
| Slab-on-grade | A concrete slab poured on the ground, with no space underneath | Settlement, heave, cracks, plumbing problems under the slab | Floor almost level with the ground; no vents or crawl space door |
| Crawl space | The house sits on a continuous foundation wall, with a short space underneath | Localized settlement, interior piers or posts that move, sill plates and rim joists damaged by moisture | Vents or a small access door in the foundation wall |
| Basement | A full level below grade | Block: horizontal cracks, bowing, water through mortar joints. Poured concrete: shrinkage cracks, water through cracks | Stairs down, exposed foundation walls |
| Pier and beam | The house rests mainly on separate piers or posts that carry beams | Uneven settlement between supports, piers or posts that move, beam deterioration, poor bracing | Visible piers, or curtain walls between them |
Typical problems are from Daniel Mercer’s experience with homes in Virginia.
Slab foundations
A slab-on-grade foundation is a concrete slab poured directly on the ground, with no space underneath. This type is more common in relatively recent homes. Typical issues are settlement, heave (the ground pushing the slab up), cracks and plumbing problems under the slab. What sets it apart, as our structural contributor Daniel Mercer points out, is that there’s no way to get underneath to look.
Crawl space foundations
In a crawl space foundation, the house is raised on a foundation wall around the perimeter, with a short space underneath for plumbing, wiring and ductwork. In Virginia you find crawl spaces in homes of just about every age. The problems Daniel sees most are settlement in specific areas, piers or posts inside the crawl space that move, and moisture damage to sill plates and rim joists. For how crawl spaces work and how to keep them dry, see our crawl spaces guide.
Basement foundations
A basement is a full level below grade. The foundation walls can be poured concrete, concrete block or, in some older homes, stone. Because those walls hold back soil, the main concern is the soil and water pressing against them. Block walls commonly show horizontal cracking, bowing and water coming in through the mortar joints. Poured concrete walls typically have shrinkage cracks and water getting in through the cracks. They can also move or bow, but they don’t have mortar joints that can give way. See horizontal cracks and bowing walls and basement water.
Pier and beam vs. a crawl space
These two are easy to confuse because you can crawl under both. A perimeter-wall crawl space has a foundation wall that runs almost continuously around the house. With a pier-and-beam foundation, the house is supported mainly on a series of piers or posts carrying beams. There may be curtain walls between the piers, but they don’t necessarily support the house in the same way. Daniel asks homeowners one simple question: is the house supported continuously on the outside wall, or mainly on separate points?
Uneven settlement from one pier to the next is common with this type of foundation. You can also see posts or piers that move, beams that deteriorate and lateral movement if the structure isn’t properly braced. Pier and beam is common in older homes, in rural areas and in some coastal areas.
Poured concrete, block or stone
In Virginia, Daniel sees stone and brick mostly in homes built in the 1800s and early 1900s, and concrete block in many mid-century and postwar homes. Poured concrete is very common in homes built from the second half of the 20th century on. He wouldn’t use the foundation to date a house precisely, though, and he has seen exceptions to every one of these patterns.
Concrete block. With block, Daniel pays close attention to lateral pressure. If a block wall isn’t reinforced enough, it can open up along the horizontal mortar joints and move toward the inside of the house. Water can also move through the hollow cores of the blocks.
Poured concrete. Poured concrete is cast as one solid piece. When it’s designed correctly, it can resist lateral pressure very well. But if it cracks, water can travel through that crack easily.
Stone. Stone slows you down. It’s very strong in compression, but in an older home you may not know what kind of footing it sits on, how the wall is tied together or what condition the mortar is in inside the wall. Daniel wouldn’t call a stone foundation weak just because it’s old. But he wouldn’t treat it like a modern poured concrete wall either.
How to tell which one you have
You should be able to tell what you have without cutting into anything. Just don’t rely completely on the real estate listing. Daniel has seen “slab” listed for a house that had a crawl space, and “concrete foundation” listed for a house where only part of it sat on a concrete foundation.
Outside
- A continuous concrete or block wall around the base of the house
- Vents in the foundation wall
- A crawl space access door
- Exposed piers
- How high the floor sits above the ground
- A slab almost level with the ground
Inside
- Stairs down to a basement
- Exposed foundation walls
- A crawl space access opening
- Floor joists you can see from below
- A concrete slab floor
In the paperwork
- Old plans
- Permits
- Previous inspection reports
- The appraisal
- County property records
Where to go next
- You see a crack: foundation cracks
- A basement wall has a horizontal crack or bows in: horizontal cracks and bowing walls
- Soft or damaged wood where the house meets the foundation: sill plates and rim joists
- Anything else in a crawl space: crawl spaces
- Water coming into the basement: basement water
Daniel Mercer’s observations come from residential work in Virginia; foundation types and building practices vary by region.
Structural information reviewed for technical accuracy by Daniel Mercer. This content is educational and is not a substitute for an on-site evaluation by a licensed professional engineer.
In this section
Foundation cracks: types and when to worry
How to read a foundation crack by direction, shape and movement, how to monitor it, and the signs that mean it's time to call a structural engineer.
Horizontal cracks and bowing basement walls
Why basement walls bow, how to measure and document the movement, the repair options and their limits, and what each one costs in 2026.
Sill plates and rim joists: what they are and how they fail
What sill plates and rim joists are, what Virginia's code requires for anchor bolts and sealing, how they rot or get termites, and what a repair costs.