Crawl Space Repair: The Four Jobs and How to Sequence Them

Crawl space repair is really four different jobs wearing one name — fixing the structure, fixing the water, fixing the moisture, and fixing the mold and pests — and the costly mistake almost every homeowner makes is doing them in the wrong order. A contractor seals a damp crawl space, or levels a floor that is still sitting over standing water, and twelve months later the same problem is back. The single rule that saves the most money here is the same one that governs every pier-and-beam repair: stop the water first, always. Get the sequence right and a crawl space stays fixed for decades; get it wrong and you pay twice.

This page is the service overview. It tells you what actually goes wrong under a pier and beam home, how each problem is fixed, and — the part the search results skip — what order to do the work in and who to hire for which piece. The structural deep dive (the re-leveling sequence, pier and beam design) lives on the pier-and-beam pages; the moisture-system deep dive lives on the encapsulation page. Here we connect them. Every threshold and cost below is drawn from building-science sources — the International Residential Code, ASHRAE Standard 160, the EPA, the USDA Forest Products Laboratory, and the ASCE Texas Section guidelines — not from a contractor's sales sheet.

The four kinds of crawl-space repair

When someone says "I need crawl space repair," they could mean any of four categories of work, with different methods, different crews, and very different price tags. Sorting your problem into the right box is the first move, because the categories also have to be done in a specific order (covered below).

The four categories of crawl-space repair, with the problems, fixes, and trade behind each.

The reason this table matters: a quote that bundles all four into one flat number, or that proposes only the one your caller happens to sell, is not a diagnosis. The honest path is to find out which boxes apply — and that is a job for measurement, not a sales call.

Structural repair (summarized — the deep dive is pier-and-beam)

The structural side is where the big dollars and the engineering live, and it is fully covered on the pier and beam guide and the foundation leveling methods page. Here is the summary you need to route the work correctly.

Almost every structural failure under a crawl space is one of four things: piers that have settled or gone out of plumb (usually from expansive-clay movement or an undersized footing), girder beams or floor joists that have rotted (a moisture failure — more on the threshold below), floors that sag or bounce (under-sized or over-spanned joists, common in pre-1970s homes), or shims that have compressed or fallen out. They show up the same way from inside the house: sloping floors, bouncy spots, sticking doors, and drywall cracks at door corners.

The repairs, in brief:

• Re-shim and re-level. Steel shims (more durable than the historic wood ones) take up the gap that past settlement opened between pier and beam. The lift itself is done gradually, in small increments — professionals raise synchronized jacks a fraction of an inch per pass and hold the structure between passes, because a sudden lift cracks the finishes overhead. The goal is structural stability and stopping further movement, not a perfectly flat floor.
• Add or replace piers. New concrete, CMU, or steel piers on new footings where existing supports have failed.
• Helical or push piers where bearing must reach a deeper, more stable stratum — see the helical piers guide. Significant lifts and any pier design are engineering decisions.
• Sister or replace rotted beams and joists. New pressure-treated lumber with galvanized (or stainless) fasteners is bolted alongside the damaged member, or the member is cut out and replaced. Because the original failure was a moisture failure, the replacement has to be specified to outlast it.

That is the whole structural story at summary depth. What this page adds is the rest of the system around it — because re-leveling a floor without fixing the water and moisture that rotted it just resets the clock.

Water and drainage

Water is the root cause behind nearly every other problem in a crawl space, which is why it is fixed first. Moisture is the master variable under a pier-and-beam home — sustained dampness is what rots the beams, feeds the mold, and invites the termites. So the first dollars go to the cheapest, highest-leverage work: bulk-water management.

That means the exterior, in order of cost: clean gutters, downspout extensions that discharge several feet from the foundation, and grading that carries surface water away from the house. The IRC asks for the ground to fall away from the foundation over the first several feet for exactly this reason. Then plumbing — a sub-floor supply or drain leak quietly soaks the soil and framing and has to be repaired before anything is sealed.

Where the problem is groundwater rather than surface water — the classic case is crawl-space dirt sitting below exterior grade, or a high water table that seeps through the walls — exterior fixes are not enough. The standard solution is an interior perimeter French drain: a trench inside the foundation walls with drain pipe in aggregate, sloped to a sump pit with a submersible pump (battery backup recommended). Address the exterior water first regardless; the interior drain handles what the grading and gutters cannot. For the drainage detail and how it ties into a sealed crawl space, see the encapsulation guide — and note the cardinal rule that encapsulation is not waterproofing. Sealing a liner over a space that still takes on water is the wrong first move.

Moisture control

Once the bulk water is handled, the remaining job is to stop ground moisture and humid air from keeping the wood damp. This is the vapor-barrier-versus-encapsulation question, and the building science has moved decisively toward sealing in humid climates.

A bare-soil crawl space evaporates ground moisture straight into the framing, and in a vented crawl, warm humid outdoor air enters the vents, hits cooler surfaces, and condenses — adding moisture rather than removing it. The fix is, at minimum, a Class I vapor barrier over the soil (code minimum is 6-mil polyethylene; durable encapsulation uses a 12–20 mil reinforced liner that survives a knee on rough soil). Full encapsulation goes further: the liner runs up the stem walls and is sealed, the vents are closed, the perimeter is insulated, and a dehumidifier conditions the space.

The IRC now explicitly permits this. IRC §R408 governs under-floor space, and §R408.3 allows a sealed, unvented crawl space with a continuous Class I vapor retarder (overlapped 6 in., sealed, run 6 in. up the stem wall) plus one of several conditioning methods — including a standalone dehumidifier sized to remove 70 pints per day per 1,000 sq ft of crawl floor, a method formally recognized in the 2024 IRC. A correctly conditioned crawl space holds relative humidity around 45–55%, comfortably under the 60% the EPA flags as a mold risk. Full encapsulation is a $5,000–$15,000 job, and the vapor-barrier-only and full-system options are compared in depth on the encapsulation page.

Mold and pests

Mold and pests are symptoms of a moisture problem, not standalone diseases — which is why they are remediated after the water is stopped, so they do not simply return. The thresholds are worth knowing because they tell you when wood is actually at risk rather than just damp:

• Wood-decay fungi (brown rot, white rot) need sustained wood moisture above roughly 28–30% — the fiber-saturation point — to initiate decay, per the USDA Forest Products Laboratory Wood Handbook.
• Surface mold can grow at lower wood moisture, around 16%, per ASHRAE Standard 160.
• Indoor relative humidity above 60% supports mold, per the EPA.
• Subterranean termites are widely reported as conducive at wood moisture around 20%.

Treat these as risk indicators, not bright lines — but they all point the same direction: keep the wood dry and the biology stays quiet. For remediation, the EPA's guidance is to keep humidity below 60%, dry wet materials within 24–48 hours, and call a professional for any mold area larger than about 10 square feet. On exposed framing, a borate treatment helps prevent fungal regrowth. For pests, the prevention basics are eliminating wood-soil contact, clearing cellulose debris, keeping a termite inspection gap, and a current WDI/termite program. Active infestations and significant rot rebuilds belong to licensed pros, not a do-it-yourself afternoon.

The right sequence

Everything above only works in one order. This is the most important paragraph on the page, because the sequence — not the individual fixes — is what separates a durable repair from an expensive redo.

1. Stop the water. Gutters, downspouts, grading, plumbing leaks; interior French drain and sump where groundwater intrudes. Nothing else holds until the water is handled.
2. Stabilize the structure. Re-shim and re-level, add or replace piers, sister or replace rotted beams and joists — gradually, to an engineer's scope for anything significant.
3. Control the moisture. Vapor barrier or full encapsulation, sealed vents, and a properly sized dehumidifier targeting 45–55% RH.
4. Maintain. Inspect at least annually and after major storms; service the dehumidifier and sump yearly; expect a maintenance reshim every 5–8 years in expansive-clay regions.

Why the order is non-negotiable: moisture is the master variable, so sealing it in before you have removed the water source guarantees the trapped moisture keeps rotting wood you have sealed out of sight. And lifting a structure that still sits over an active water problem just re-creates the differential movement that bent it in the first place. Water, then structure, then moisture, then maintenance — every time.

What it costs (quick view)

Crawl-space repair has no single price because it is four jobs. These are 2025–2026 national planning ranges, not quotes; access difficulty (a 24-inch crawl is far harder to work than a 4-foot one) is the largest single multiplier, and the full Texas breakdown is on the crawl space cost page.

Crawl-space repair cost ranges, 2025–2026 national averages. Which lines apply to you is the whole question — and that is what the engineer's report answers.

How to hire (engineer-first)

The hiring rule for crawl-space repair is the same one that governs all foundation work, and it is worth stating plainly: engineer first, contractor second. Foundation diagnosis is the practice of engineering, not contracting — the ASCE Texas Section has said so for years. An independent Professional Engineer has no financial incentive to recommend more piers, more beams, or more encapsulation than your house needs.

So the workflow is: get an independent PE's sealed scope for any structural work before you take bids (an engineer's report is $500–$1,500), then bid that scope to two or three specialists. Demand an itemized, per-pier, per-beam, per-joist line-item quote — a good scope reads like a parts list, and any flat "fix the crawl space" number is a bet that favors the contractor. The two hardest red flags to ignore: an online or over-the-phone encapsulation quote with no on-site inspection, and the company that "inspects" for free then writes your structural scope. Moisture-only work — a vapor barrier, a dehumidifier — can usually go straight to a qualified contractor; it is the structural scope that needs the engineer's seal.

FAQ Note

The FAQ below answers what homeowners ask most once a first contractor has been under the house — what the work includes, what order it happens in, what it costs, whether you need an engineer, how to tell structural damage from a moisture problem, and how urgent mold or rot really is. For the structural detail behind the summary above, start with the pier and beam guide; for the moisture system, see encapsulation; and for a second opinion before signing anything, an engineer's report is the cheapest insurance you can buy.

Get Matched With a Vetted San Antonio Crawl-Space Specialist

If your crawl space has a problem — a floor you can feel slope, a musty smell when the AC kicks on, or water on the soil after a storm — the right next step is a measurement and a sequence, not a one-line quote. We'll match you with a vetted San Antonio specialist and point you to an independent engineer who can sort your problem into the right box — structure, water, moisture, or pests — and put the work in the right order. The match is free, the quote is no-obligation, and we don't take a fee from you. We screen for sealed-engineer diagnosis on any structural scope, itemized per-pier line-item quotes, an on-site inspection before any encapsulation bid, and a water-first sequence — because on a pier-and-beam home, the order is what makes the repair last.