Ventilated crawl spaces are common in older homes because they sound like a good idea. In theory, open vents in crawl spaces should improve air circulation and allow accumulated moisture to vent outdoors. The problem is these vents often do just the opposite, especially in humid Michigan. The vents let in more moisture than they let out.
That moisture soaks into the fiberglass batt insulation in the floor, eventually making it so soggy it can’t insulate effectively. Worse yet, warm, moist crawl spaces form the perfect breeding ground for mold and dust mites. Mold and mites then end up in your home, lowering your indoor air quality.
Current best practices include the crawl space(s) as part of the home’s conditioned space. To upgrade your crawl space to keep out moisture you’ll need to do more than just seal the vents.
Redirect water sources – Gutters, downspouts, patios, sidewalks, and your lawn should all direct water away from the house. You may need to extend your downspouts or regrade your lawn and sidewalks.
Properly insulate the crawl space walls – Use rigid foam insulation, which is less susceptible to water damage than fiberglass or cellulose. Of all rigid insulation types, polyisocyanurate (PIR) offers the highest insulating efficiency. Avoid insulating the ceiling.
Install a vapor barrier – A vapor barrier is a thin plastic or foil sheet that provides an extra layer of protection against moisture infiltration. Place one over the crawl space floor and six inches up the walls. Use tape and landscape fabric stakes to secure the barrier.
Seal the vents – Cover vents from the outside using metal vent covers attached with screws or plywood attached with caulk.
Seal the rim joists – Use foam sealant to attach rigid board insulation to the ends of joist bays.
Seal exterior access hatches – Install a weatherproof crawl space hatchway door or seal your existing hatchway cover with heavy-duty weatherstripping.
If you’re tired of dealing with rotting insulation and mold in your ventilated crawl spaces, contact us at Team Bob’s Heating Cooling Plumbing. Since 1980, we’ve been helping Grand Traverse County residents keep their homes comfortable and safe.
Our goal is to help educate our customers in Traverse City, Michigan and surrounding areas about energy and home comfort issues (specific to HVAC systems). For more information about ventilated crawl spaces and other HVAC topics, download our free Home Comfort Resource guide.
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