Crawl Space Encapsulation

Crawl Space Building Science

One of the biggest advances in building science over the past  decade is the research that proves definitively that vented crawl spaces are bad.
If you’ve ever been in one, you know it’s true. They’re damp. They’re dark. Critters have easy access to them. The batt insulation falls down. The air smells musty & moldy. And the crawl space communicates with the house, so that bad air (and the occasional critter) gets into the living space above.
In 2002, Advanced Energy studied a group of 12 houses in North Carolina. What they found is that the 8 that had encapsulated crawl spaces had relative humidity that stayed less than 60% all summer, whereas the 4 vented crawl spaces had humidity levels that tracked the outdoor humidity. (The terms closed crawl space, sealed crawl space, and conditioned crawl space are sometimes used to describe crawl space encapsulation as well.)
The reason the vented crawl spaces had higher humidity is actually pretty simple. Warmer air can hold more moisture, so in the summer time, the outdoor air can bring a lot of extra water vapor with it when it comes into a crawl space through the vents. When that warm, humid air comes into the crawl space and cools off, the relatively humidity can go even higher.  Vented crawl spaces have a number of problems that seriously degrade a home’s performance. The best alternative is to encapsulate the crawl space, or else design it away altogether if you’re building new.


The photo above shows what an encapsulated crawl space looks like. Although any color vapor barrier will work, using white makes the crawl space bright and cheery. (So cheery, in fact, that you might need to lock it to keep the kids from turning it into a playroom.)
Here are the basic features of an encapsulated crawl space:
• 100% coverage of the ground with a vapor barrier
• Seams and junctions of vapor barrier sealed
• Sealed crawl space vents
• Insulated foundation walls and band joist (usually)
• Conditioning of air with one of three methods: (i) dehumidifier, (ii) small amount of supply air from HVAC system, or (iii) small exhaust fan
The benefits of this treatment are significant. As shown in the first article of this series, the relative humidity will stay below 60%, even when the outdoor humidity is much higher. With dehumidification, it’s not difficult to reduce the humidity to less than 50%.
Some other benefits are:

Better air quality in the crawl space, which means better air quality in the living space
• Greater energy efficiency. The Advanced Energy studies have found nearly 20% reduction in energy use in homes with a conditioned crawl space.
• Fewer critter problems
• Greater durability of floor, HVAC equipment, and other components in the crawl space
• Greater comfort in the home because of reduced humidity and crawl space temperatures close to living space temperatures

Rim joist/sill plate area properly sealed unto liner———-and not always in the best conditions….

another-great-day-in-a-crawl-space crawl-space-with-liner-and-rj-sprayed

Ask us why we never insulate the floor!!