OPEN CRAWL SPACE VENTS ARE MAKING YOUR MOISTURE PROBLEM WORSE

If your Twinsburg home was built before 1990, there's a good chance you have foundation vents in your crawl space walls. They're those small, louvered openings at ground level — usually one on each side of the house. For decades, building code required them.

The theory made intuitive sense: let fresh air flow through the crawl space to carry moisture out. But decades of building science research have proven that theory wrong — especially in humid climates like Northeast Ohio's.

WHY VENTED CRAWL SPACES GET WETTER, NOT DRIER

Here's the physics. During a typical Ohio summer, outdoor air temperatures reach 85°F or higher with dewpoints of 65 to 70°F. That air is carrying a significant amount of water vapor. When it enters your crawl space through those open vents, it meets surfaces that are much cooler — the earth floor sits at around 55°F, and the foundation walls, metal ductwork, and floor joists aren't much warmer.

When warm, humid air contacts a cool surface, it condenses. This is the same process that puts water droplets on a cold glass on a summer day. In your crawl space, that condensation coats your joists, your HVAC ducts, your subfloor, and any insulation in the space. You're not ventilating moisture out — you're pumping it in and creating conditions for mold growth, wood rot, and structural damage.

THE RESEARCH IS CLEAR

Advanced Energy, a North Carolina-based building science research organization, conducted one of the most comprehensive studies on this topic. They monitored identical homes — some with vented crawl spaces, some sealed — over multiple years. The sealed crawl spaces consistently maintained lower humidity, less mold, and better structural conditions.

The Building Science Corporation reached the same conclusion. Their research showed that sealed, conditioned crawl spaces outperform vented ones in every measurable way in humid climates — lower moisture levels, fewer pest intrusions, better energy efficiency, and dramatically less mold.

This research changed the building code. Modern Ohio building code now allows and actively encourages sealed and conditioned crawl spaces as an alternative to vented ones. New construction in Summit County frequently uses sealed crawl space designs.

WHAT TO DO ABOUT YOUR OPEN VENTS

Simply closing or blocking the vents isn't enough. Without a moisture management system in place, sealing vents alone can trap existing moisture and make things worse. The correct approach is a complete system:

Seal the vents permanently — not with duct tape or foam, but with solid vent covers that are mortared or caulked to the foundation wall.

Install a vapor barrier — a heavy-duty 20-mil polyethylene liner over the entire crawl space floor, sealed to the walls and all penetrations. This stops ground moisture from evaporating into the space.

Add a dehumidifier — a commercial-grade unit sized for your crawl space volume. This handles any residual moisture and maintains humidity below 55%, the threshold that prevents mold growth.

Together, these three steps transform a vented crawl space into a conditioned one. This is exactly what a full crawl space encapsulation system provides. The result is a dry, clean, controlled environment that protects your home's structure and the air quality upstairs.

CHECK YOUR CRAWL SPACE THIS SUMMER

Summer is when open-vent damage accelerates fastest. If you have foundation vents and haven't inspected your crawl space recently, it's worth a look — or better yet, a professional assessment. We offer free crawl space inspections for Twinsburg-area homeowners, and we'll measure the actual humidity levels so you can see the numbers for yourself.