Home › Services › Crawl space encapsulation around Huntsville
Encapsulation means turning the crawl space from a vented, outdoor-ish space into a sealed one: heavy plastic over the dirt and up the foundation walls, the vents closed, and a machine or a duct keeping the air dry. Around Huntsville it is usually sold after somebody finds mold on the joists, sweating ductwork, or a floor that smells musty every July. Done well, it ends the summer condensation cycle. Done badly, it traps water under a liner where nobody looks. This page covers what a sound job includes so you can read a quote line by line.
The problem here is mostly summer air, not rain. NOAA's 1991–2020 hourly normals for Huntsville International Airport average a July dew point of about 70°F, and the normal dew point sits at 60°F or higher for roughly 3,000 hours a year, every one of them between May and September (NCEI hourly normals). Any joist, duct or pipe below that temperature collects water. The U.S. Department of Energy's Building America research found that in humid climates the outside air is often wetter than the crawl space air, so foundation vents bring moisture in, and that closed, conditioned crawl spaces lowered humidity by more than 20 percent (DOE). If you want to see whether your own framing is below the dew point, the crawl space condensation calculator does the arithmetic from a thermometer and hygrometer reading.
A liner over active growth or a wet floor just hides the problem. Before sealing, existing mold on joists and subfloor should be cleaned, soaked insulation pulled out, and any liquid water dealt with: downspouts that dump against the block, yard grading that slopes toward the house, a plumbing drip, or groundwater that seeps in after a wet spring. Some crawl spaces need a perimeter drain and a sump before any plastic goes down. Our crawl space mold page covers the cleanup half of the job.
The Department of Energy's weatherization job aid for crawl space vapor retarders gives a useful floor to measure any quote against (DOE job aid 16-1):
| Item | DOE job aid minimum | What to ask |
|---|---|---|
| Material | 6-mil or thicker, perm rating 0.1 or less | Many encapsulation liners are much thicker and reinforced. Ask the mil rating in writing. |
| Coverage | 100 percent of the ground, or as close as reasonably possible | Does it wrap every pier and run under the HVAC platform? |
| Walls and piers | At least 6 inches up walls, columns and footings, mechanically attached where needed | Full-height wall coverage or a 6-inch turn-up? Both exist. |
| Seams | Overlapped at least 12 inches, lapped upslope | Taped? Sealed with what? |
| Edges (sealed crawl spaces) | Sealed to the foundation and supports with mastic or acoustical sealant | How are the vents and the access door closed off? |
| Drainage | The liner must not block existing drainage paths | Where does water go if a pipe leaks on top of it? |
Closing the vents removes the old ventilation, so something else has to control moisture. The International Residential Code's unvented crawl space section (R408.3) pairs the sealed ground cover with one of a few options: a small exhaust fan, a supply of conditioned air from the house system, or a dehumidifier. Alabama adopts the IRC with state amendments and leaves enforcement to local building departments (American Wood Council), so ask the City of Huntsville, Madison or your county inspector which edition applies and whether the job needs a permit.
If the contractor recommends a dehumidifier, the questions that decide whether it works for years are practical ones: what capacity it is and how that was sized for your square footage, where the condensate drains (gravity to daylight, a condensate pump, or the sump), whether it has a filter that someone has to change, and who you call when it stops. A supply-air approach has no machine to maintain but changes the HVAC system, which is work for a licensed HVAC contractor.
Madison and Limestone are on the Alabama Department of Public Health's list of 15 counties with the highest potential for elevated radon, and ADPH offers one free test kit per household while supplies last (ADPH, January 2026). DOE notes that a well-installed ground cover helps limit soil gases such as radon. Sealing changes how air moves under the house, so a test before and after encapsulation tells you where you stand.
Prices come from the contractor after a site visit. For a sense of scale, Bob Vila's cost guide gives these national figures (Bob Vila):
A combined job with drainage, cleanup, liner and dehumidifier can pass $10,000. In Alabama that matters: the Home Builders Licensure Board requires a state home builder license and a written contract for residential work above that amount (HBLB). The Alabama hiring guide explains how to check a license.
It addresses the main reason vented crawl spaces here get wet: humid summer air condensing on cooler framing and ducts. DOE research found closed, conditioned crawl spaces cut humidity by more than 20 percent. It is not a substitute for fixing liquid water or cleaning existing mold, which come first.
The sealed space needs some way to control moisture. Code options include a dehumidifier, a small exhaust fan, or conditioned air from the house system. Which one fits depends on the house and the HVAC setup, so ask the contractor why they picked theirs.
It depends on the jurisdiction and the scope, especially if HVAC, electrical or drainage work is involved. Ask the city or county building department before work starts, and expect the contractor to know the answer.
This site is a referral line, not a cleanup crew. Send your town and what you have found, and an independent local mold company will follow up with you. Water still coming in? Shut it off at the source first, then reach out.