A pier and beam foundation holds a house up off the ground on a grid of short columns (piers) that carry beams, and the beams carry the floor joists. The result is a raised wood floor with a crawl space underneath, instead of a floor poured directly on the soil like a slab.
It is a common foundation for older homes and for sites with expansive clay, sloping ground or a high water table. This guide covers how the system carries load, what each part does, how it compares with a slab, the crawl space rules that keep it dry, and the problems and repairs owners run into most often.
How a Pier and Beam Foundation Works
Every foundation has one job: take the weight of the house, its contents and the people in it, and spread that weight into the soil. A pier and beam foundation does it in steps. The floor sheathing sits on joists. The joists span between beams. The beams sit on piers. Each pier sits on a footing that is wider than the pier, so the load is spread over enough soil to keep it from sinking.
Around the outside, the joists usually bear on a sill plate and rim joist that sit on either a continuous perimeter wall (a stem wall) or a perimeter beam on its own row of piers. Inside, one or more lines of beams and piers break the floor into spans the joists can handle.
The Parts of a Pier and Beam Foundation
Footings
Footings are pads of concrete under each pier. Their size depends on the load and on how much pressure the soil can take, and their depth has to get below the local frost line in cold climates. A footing that is too small settles; one that is too shallow can be lifted by frost.
Piers
Piers are the short columns between footing and beam. Older homes often have brick or concrete block piers, or wood posts. Newer work uses poured concrete, reinforced block, or steel posts. Adjustable steel posts of the kind covered in our lally column guide are also used, though in a crawl space they need protection from moisture and corrosion.
Beams (girders)
Beams run across the tops of the piers and carry the joists. The longer the distance between piers, the deeper or stronger the beam has to be. Common choices are listed below.
| Beam type | Typical use | Trade-offs |
|---|---|---|
| Built-up dimensional lumber (2x boards nailed together) | Most older and many new homes | Cheap and easy to cut on site; short spans; can rot or be attacked by insects in a damp crawl space |
| Engineered wood (LVL, glulam) | Longer spans, fewer piers | Stronger and straighter than sawn lumber; must be kept dry and installed to the maker’s details |
| Steel wide flange (W shape) | Long spans, heavy loads, low headroom | Carries more load for its depth; needs corrosion protection, heavier to handle, and wood-to-steel connections |
Headroom is tight in most crawl spaces, so depth matters. According to the AISC Shapes Database v16.0 (the data behind our charts, checked October 2026), a W8x10 is 7.89 in deep with a 3.94 in flange, and a W6x12 is 6.03 in deep with a 4.00 in flange. Which size, if any, works for a given span is a job for a licensed structural engineer; our steel beam span chart shows how span and load interact, and the basement support beam guide covers similar beams in basements.
Joists, sill and rim
Floor joists span from beam to beam or from beam to the perimeter. Their size and spacing set how stiff the floor feels; see our floor joist spacing article for the usual layouts. At the outside edge, the joists end at a rim joist resting on a sill plate, which should be treated wood where it touches concrete or masonry.
Pier and Beam vs Slab Foundation
| Factor | Pier and beam | Slab on grade |
|---|---|---|
| Access to plumbing, ducts and wiring | Easy from the crawl space | Under-slab pipes need the slab cut open |
| Sloping or uneven sites | Pier heights can vary to suit the ground | Needs grading or a stepped design |
| Flood-prone or wet sites | Floor sits above the ground | Floor sits at or near grade |
| Moisture and pests | Crawl space must be kept dry and inspected | No crawl space to manage |
| Floor feel | Wood floor with some give | Hard, solid floor |
| Leveling later | Can be shimmed or re-leveled from below | Usually needs slab jacking or piering |
Neither is better everywhere. Soil, climate, flood risk and local building practice usually decide it, and a geotechnical report is the best guide on a new build.
Crawl Space Ventilation and Moisture
Most of the long-term problems with pier and beam houses start with water. Damp air in a crawl space feeds wood rot, mold, insects and rust on steel parts. The International Residential Code deals with this in Section R408, and gives two routes.
Vented crawl space
As quoted from the 2009 IRC in Penn State’s PHRC Fundamentals of Crawlspace Design and Construction (checked October 2026), the under-floor space needs at least 1 square foot of net vent opening for every 150 square feet of crawl space area. If the ground is covered with a Class I vapor retarder, that drops to 1 square foot per 1,500 square feet. One vent has to be within 3 feet of each corner of the building.
Unvented (sealed) crawl space
The same code section allows a crawl space with no outside vents if the ground is covered with a continuous Class I vapor retarder, lapped 6 inches at seams and run 6 inches up the walls, and the space gets either continuous exhaust or conditioned air at 1 cubic foot per minute for each 50 square feet of floor area, with the walls insulated. The PHRC paper explains why this is often the better choice in humid summers: warm outdoor air entering a cooler crawl space can reach 100 percent humidity and condense on the framing.
Code editions and local amendments vary, so check which version your jurisdiction has adopted before planning vents or encapsulation.
Common Pier and Beam Problems
HUD’s Residential Rehabilitation Inspection Guide (section 4.4, checked October 2026) notes that piers often settle unevenly and, when exposed to the weather, deteriorate over time. The problems it lists are:
- Footing settlement or rotation, which lowers or tilts the pier so it carries less load. Wood framing above sags; masonry walls above crack.
- Frost heave, where a footing that is too small or too shallow gets pushed up, most often under porches.
- Deterioration of the pier itself from weather, poor construction or overload. HUD names vertical cracking or bulging as a sign of an overstressed pier.
- Loss of bearing, where beams or joists no longer sit fully on their supports.
Inside the house these show up as sloping or bouncy floors, doors that stick or swing open, gaps at baseboards, and cracks over doors and windows. Under the house, look for leaning piers, beams that have slid off their supports, crushed or rotted shims, sagging joists, standing water and damp or stained wood.
How Pier and Beam Foundations Are Repaired
Re-shimming and leveling
Where a pier has settled slightly, the beam can be jacked back up a little at a time and packed with durable, non-compressible shims. Raising a floor quickly can crack plaster, drywall and tile, so contractors usually lift in small stages.
Adding or replacing piers
Failed piers are replaced with new ones on properly sized footings. Extra piers can also be added to shorten a beam span that was too long to begin with.
Beam and joist repairs
Rotted or undersized beams are replaced, sometimes with LVL or steel. Cracked or sagging joists are often sistered with a new joist fastened alongside. Fixing the moisture source has to come first, or the new wood goes the same way as the old.
Changing piers, beams or spans alters how the structure carries load. A licensed structural engineer should size new beams and footings, and most jurisdictions require a permit for foundation work.
Pier and Beam Foundation FAQ
What is the difference between pier and beam and a crawl space foundation?
They overlap. Pier and beam describes how the floor is held up; crawl space describes the open space it leaves. A crawl space house can also sit on continuous foundation walls with few or no interior piers.
How far apart are piers in a pier and beam foundation?
There is no single spacing. It depends on the beam size and material, the load, and the footing and soil. Stronger beams can span farther between piers. The spacing should come from a design or the span tables your local code accepts.
Are pier and beam foundations good?
They work well when the footings are sized and deep enough and the crawl space is kept dry. Their big advantages are easy access to utilities and the ability to re-level from below. Their main weakness is moisture.
Can I use a steel beam in a pier and beam foundation?
Yes. Steel wide flange beams are used where spans are long or headroom is limited. They need corrosion protection in a crawl space and proper connections to the piers and joists, and an engineer has to size them.
Why are my floors sagging on a pier and beam house?
Common causes are settled or deteriorated piers, crushed or missing shims, rotted beams or joists, and beam spans that were too long. A crawl space inspection will usually show which one it is.
Reference information only, not engineering advice. Disclaimer.