Crawl Space Encapsulation and Repair in Oklahoma City

Why so many OKC homes have crawl spaces

Pier-and-beam homes rest on posts or piers with a wooden floor frame above a shallow crawl space, instead of sitting directly on a concrete slab. Builders in Oklahoma City used them widely before slabs became standard, which is why they are concentrated in the older core of the city.

Census data we pulled for the metro shows how old some of these neighborhoods are:

ZIP	Area	Homes built before 1960	Median year built
73107	West-central Oklahoma City	72%	1949
73103	Downtown and Midtown	71%	1938
73118	North-central Oklahoma City	69%	1947
73106	Central Oklahoma City	61%	1942
73119	Southwest Oklahoma City	52%	1959

Not every older home has a crawl space, but many do, and a 70-year-old crawl space has had plenty of time to collect moisture problems. Learn how the two foundation types behave in our guide to pier-and-beam vs slab. If your floors already feel soft or bouncy, a local foundation specialist can crawl under and tell you what is going on.

Signs your crawl space has a problem

• A musty or earthy smell inside the house, especially in summer
• Floors that sag, bounce or slope, or gaps under baseboards
• Standing water, mud or damp soil under the house
• Wet or fallen insulation hanging from the floor framing
• Visible mold, white fuzz or dark staining on joists and beams
• Rusty ductwork, sweating pipes or condensation on surfaces
• Termite tubes or soft, crumbly wood

Soft or sagging floors deserve a closer look because they can mean either moisture damage to the wood or movement in the piers. A photo of what you are seeing is a quick way to start.

Why crawl spaces get damp, and the vent debate

Older codes required vents in crawl space walls, on the theory that outside air would dry things out. Building science research has shown that this often backfires in humid summers.

Joseph Lstiburek of Building Science Corporation explains that crawl space ground is much colder than summer outdoor air. When warm, humid air comes in through the vents, it meets cool surfaces and the moisture condenses on the wood and insulation. The US Department of Energy's Building America program makes the same point: in humid climates, outside air is often wetter than the air already in the crawl space, and humid crawl spaces are tied to structural, mold and pest problems.

A field study by North Carolina's Advanced Energy, sponsored by the Department of Energy, compared closed and vented crawl spaces in matched houses in the Southeast. It found that a properly closed crawl space was much drier and cut annual heating and cooling energy use. DOE says this research helped shape changes to the 2009 and 2012 International Residential Code (section R408.3) that allow unvented, conditioned crawl spaces.

The catch is that closing the vents only works if you also control moisture. The EPA notes that "the key to mold control is moisture control" and recommends keeping indoor humidity below 60%, ideally 30 to 50%.

Vapor barrier, encapsulation or repair: which do you need?

Vapor barrier only

A vapor barrier is a plastic sheet laid over the dirt floor to stop ground moisture from evaporating into the crawl space. It is the most basic step and often the right one for a crawl space that is dry but has bare soil. Vents usually stay open.

Full encapsulation

Encapsulation turns the crawl space into a sealed, conditioned part of the house. A typical job includes:

• A heavier liner over the floor, overlapped and taped at the seams and run up the walls. The model code (IRC R408.3) calls for a continuous Class I vapor retarder with seams overlapped 6 inches and sealed, carried at least 6 inches up the wall.
• Sealing the vents and other openings to the outside
• Insulating the foundation walls instead of the floor above
• Drying the air with a dehumidifier, a small conditioned air supply, or an exhaust fan, as the code requires for unvented crawl spaces

Requirements vary by city, so the contractor should confirm what your local code office expects.

Crawl space repair

Repair is structural: replacing rotted joists or sill plates, adding support posts, or re-shimming piers that have settled. A shim is a thin spacer driven between a pier and a beam to bring the floor back to level. If the floor is sagging, encapsulation alone will not lift it. Repair usually comes first, then moisture control so the problem does not return.

Fix the water first

None of these work if water is pouring into the crawl space from outside. Gutters, grading and sometimes an interior drain come first. See our guide to French drain installation in Oklahoma City.

What crawl space encapsulation costs

These are national ranges from published cost guides, not quotes. Your price depends on size, height and access, how wet the space is, and what repairs are needed first.

Work	Published range	Source
Full encapsulation	$3 to $10 per sq ft; $3,000 to $15,000 total	HomeGuide
Full encapsulation	$1,500 to $15,000; about $5,500 average; $3 to $7 per sq ft for basic jobs	This Old House
Vapor barrier, installed	About $2 to $4 per sq ft	HomeGuide
Dehumidifier, installed	$1,000 to $3,000	HomeGuide
Crawl space insulation	$1.00 to $4.50 per sq ft; $500 to $3,700 total	HomeGuide
Interior crawl space drain	$800 to $3,000	HomeGuide
Crawl space repair	$500 to $8,000	HomeGuide
Mold remediation in a crawl space	$1,500 to $4,000	HomeGuide

This Old House notes that labor is typically 50 to 70% of the total. Structural work on the piers and beams is priced separately; our foundation repair cost guide covers that side.

Questions to ask before you sign

1. Is the floor sagging from wet wood, from settled piers, or both? What do you recommend fixing first?
2. Where is the moisture coming from: the ground, outside air, a plumbing leak, or surface water?
3. Do I need full encapsulation, or would a vapor barrier and drainage fixes be enough?
4. How thick is the liner, how are seams sealed, and how far up the wall does it go?
5. How will the space be dried after the vents are closed, and what will that cost to run?
6. Will you measure humidity and wood moisture before and after?
7. Does my city require a permit, and who pulls it?

More hiring questions are in our guide to choosing a foundation repair company.

Start with an inspection

In an older Oklahoma City home, the crawl space is where moisture, wood and foundation problems meet. A free inspection from a local foundation specialist can tell you whether you need a simple vapor barrier, full encapsulation, structural repair, or some mix, before you pay for any of it.