Crawl space mold around Huntsville

A lot of older homes in Huntsville, Athens and the rural parts of Madison and Marshall County sit on a crawl space rather than a slab. That space under the floor is where mold most often gets a foothold, and it can go unnoticed for years because nobody crawls down there until a floor goes soft, an HVAC tech mentions it, or a home inspector writes it up during a sale.

Why summer is the problem season

Most people assume crawl spaces get wet from rain, and some do. But in North Alabama the bigger culprit is often the summer air itself. NOAA's hourly normals for Huntsville International Airport put the average July dew point around 67°F, and every hour of June, July and August averages a dew point above 60°F. Crawl spaces stay cooler than the outdoors because they're shaded and sit against the earth. When that warm, moist outside air drifts in through foundation vents and touches a cooler joist, duct or pipe, water condenses on it. The U.S. Department of Energy's Building America program describes the same thing: in humid climates, outside air is often wetter than the air already in the crawl space, so venting can add moisture rather than remove it.

Signs to look for

• White, fuzzy or dark growth on floor joists and the underside of the subfloor.
• Fiberglass batts sagging or lying on the ground because they've soaked up water.
• Ductwork or the refrigerant line dripping in summer.
• Standing water or mud after rain, or a plastic ground cover with puddles on top.
• A musty smell in rooms above, especially when the air conditioning first kicks on.
• Soft spots, cupped hardwood or floors that bounce more than they used to.

Cleaning the framing

Crawl space remediation usually means removing wet or moldy insulation and debris, then cleaning joists, beams and subfloor by HEPA vacuuming and scrubbing, with heavier methods for stubborn staining. The same EPA principles apply as anywhere else in the house: protect the people doing the work, keep spores from being drawn up into the living area, and don't consider the job finished until the moisture source is handled. Wood that has softened from rot may need a carpenter to sister or replace it, which is a separate line item from the mold work.

Keeping it from coming back

Cleaning without a moisture plan just resets the clock. Common approaches, from simplest to most involved:

1. Fix the water first. Gutters that dump at the foundation, downspouts without extensions, and yard grading that slopes toward the house all push water underneath.
2. Ground cover. Heavy plastic sheeting over bare dirt slows the moisture coming up from the soil.
3. Sealed (closed) crawl space. Vents are closed, walls are lined or insulated, and the space is dried with a dehumidifier or a small supply of conditioned air. DOE's Building America research found closed, conditioned crawl spaces cut humidity by more than 20 percent and saved 15 to 18 percent on heating and cooling in the homes studied.

Which approach fits depends on the house, drainage and budget. A sealed crawl space can raise local code questions, so ask the company whether a permit is needed in your city or county and how its design meets it. Your target, per EPA, is relative humidity below 60 percent, ideally 30 to 50.

Getting a quote

Ask for the mold cleanup and the moisture control priced as separate lines, so you can compare companies and decide whether to do them together. Crawl space work can run past $10,000 once encapsulation and wood repair are added; if it does and it includes repair or improvement to the home, see our hiring guide for the Alabama license rule that applies. Not sure the crawl space is the source? Start with a mold inspection.

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