Why do my pier-and-beam shim packs hold, then slip again?

What intermittent shim pack failure actually means

Your pier-and-beam house sits on a grid of piers. Between the top of each pier and the wood beam is a small stack of shims that fine-tunes the height and takes up the load.

Intermittent failure means that pack holds sometimes and slips other times. The floor is fine for months, then a section starts flexing or squeaking again, then it settles down.

That on-again, off-again pattern is the important clue. A shim pack that fails once and stays failed usually means crushed wood or a settling pier. One that comes and goes almost always means something is moving with the weather.

The good news: if the beams and piers are sound, re-shimming a few piers is genuinely a DIY job for a handy homeowner. The catch is figuring out why it keeps happening so you're not back under the house every season.

Why it keeps happening

The number one cause in most of the US is expansive clay soil. It swells when wet and shrinks when dry, and it can move a pier up and down by an inch or more across a year.

When the pier rises, it squeezes the pack tight. When it drops, a gap opens and the floor sags. The shims never changed, the ground under them did.

The second big cause is the shim pack itself being built wrong. Tall stacks of thin steel shims walk sideways under normal house vibration, and cheap wood shims crush once they get damp.

A settling pier is the one you don't want. If the footing is sinking into soft ground, you'll shim it, it'll drop, you'll shim it again. That cycle means the base needs fixing, not the shims.

Crawlspace moisture ties a lot of this together. Standing water keeps the soil swollen and the wood swollen, so nothing under there gets a stable footing until the drainage is fixed.

How to inspect and re-shim it yourself

Start by finding the culprit. Have someone walk the floor above while you listen from below, or just follow the squeaks and flex to the pier that's moving.

Get your floor jack on a solid base right next to the pier, not on bare dirt. A concrete block or a thick wood pad spreads the load so the jack doesn't sink.

Raise the beam just enough to take the weight off the shims. You're looking for 1/8 inch, enough to slide the old shims out with your fingers. This is not a lift.

Inspect the old shims. If they're wood and they're soft, dark, or crush under your thumbnail, they've been eating crawlspace moisture. Toss them.

Reset with pressure-treated hardwood or steel shims. Build the tightest, lowest pack you can. If you need more than about 3/4 inch of shim, the pier probably settled and you're into pro territory.

Lower the jack slowly and check that the pack is snug with no rattle. Tap a shim edge with a hammer, it should be tight, not loose.

Then wait a season and recheck. If the gap comes back, you've confirmed soil movement and the real fix is drainage or deeper footings.

• Floor jack rated above the beam load
• Jack stands or wood cribbing for backup support
• Pressure-treated hardwood or steel shims
• Headlamp, gloves, long sleeves
• Pry bar and a hammer
• Tape measure to log shim height over time

What it costs in 2026

If you're re-shimming a few piers yourself, you're mostly paying for materials. A bundle of hardwood or steel shims runs $15 to $40, and if you don't own a floor jack, a basic one is $30 to $60.

Professional repair typically runs $500–$5000. This is not a DIY job, so plan on hiring a pro.

A pro re-shim and leveling visit typically runs $500–$5000 for a handful of piers. That covers the crawl-in inspection, jacking, new shims, and confirming level across the affected area.

Where costs climb: if the pier itself has settled and needs a new footing, budget $500 to $1,500 per pier. If a beam is rotted, replacement can run $1,000 to $3,000 depending on span and access.

Drainage work is its own line item. A French drain or crawlspace sump to stop the moisture cycle usually lands between $1,500 and $6,000 depending on the layout.

DIY or call a pro

This is a reasonable DIY job if you've got crawlspace clearance, one or two loose packs, and sound wood above and below the shims. The work is simple, the risk is manageable if you cribbing under before you crawl.

Call a pro when the pattern points to something structural. A pier that keeps sinking, a beam that's soft to the touch, a gap over an inch, or more than a few piers all moving at once.

You should also call if the crawlspace has standing water and any electrical down there, or if the clearance is so tight you can't set a jack safely.

There's no shame in a diagnostic visit either. A foundation contractor can tell you in an hour whether you've got a shim problem or a soil problem, and that answer changes everything about what you spend.

Can this wait?

Short-term, a single loose shim pack won't drop your house. But it's rated high urgency for a reason: the moisture and movement causing it don't pause.

A bouncing beam works nails loose, cracks drywall, and pops tile above it. Give it a year and you'll see it in the finishes.

Worse, the same crawlspace moisture that crushes wood shims also rots beams and joists. A $70 shim job you keep putting off can turn into a $2,000 beam replacement.

If the floor is only slightly springy and you've confirmed it's seasonal, you have some runway to plan drainage work. If it's getting steadily worse or the slope is visible, don't sit on it.

Where this shows up most

Expansive clay drives most intermittent shim failures, and it's everywhere from Texas through the Gulf states and up into parts of the Midwest and mid-Atlantic.

If you're in a clay-heavy area, seasonal shim movement is almost expected on older pier-and-beam homes. The fix leans toward stabilizing moisture around the perimeter, not chasing shims all winter.

In colder climates, shallow footings that freeze and heave cause the same come-and-go pattern. Footings below the frost line solve it, but that's a rebuild, not a shim.

In dry regions with sandy or rocky soil, intermittent failure is more often about crushed wood shims or a poorly built pack than soil movement.

Older homes and original piers

Homes built before the 1960s often have brick or stacked-block piers on shallow footings, sometimes with no real footing at all. Those move more and shim more.

On these houses, a growing shim stack is common and not automatically alarming, but keep an eye on the total height. Once you're stacking past an inch, the original pier has usually settled and wants a proper footing.

Original beams in these homes are frequently old-growth wood, which is tough, but they've had decades to soak up crawlspace moisture. Probe the beam with a screwdriver near the shims before you trust it.

If the whole system is 60-plus years old and moving in several spots, a full re-level and shim reset by a pro is often cheaper than chasing individual piers over several seasons.

How we sourced this

This guidance reflects standard pier-and-beam repair practice and the failure patterns field techs see most often across US soil and climate types.

Cost ranges are 2026 US estimates for typical residential work and vary with region, access, and how many piers are involved. Get a written quote for anything structural.

When your read of the crawlspace disagrees with anything here, trust what you can see and measure under the house. Every foundation is a little different.