Benefits of Crawl Space Encapsulation (Sealing)

moldcrawlspaceShould I Seal My Crawl Space?
Water can cause major problems if ignored and left to build up in a crawl space, or anywhere else in a building, for that matter. This is why, here at EPB, we like to do full crawl space encapsulations, using vapor barriers. We recommend this for anyone who has a risk of moisture build-up (which is most homes), and wants improved air quality in their home and improved home efficiency. Also, anyone who has duct work in the crawl space will benefit even more, since the encapsulation will protect and partially insulate the ducts.

Sources of Humidity in Homes and Crawl Spaces
External Sources
Water can get into a crawl space in a few different ways. Humid climates are definitely the biggest cause of moisture problems, but they aren’t the only one. Water can come up through the soil, which is very common. Depending on soil type and the water table, moisture often continually comes from the soil in a crawl space all year around. It can also come from irrigation, or it can happen naturally during the rainy seasons. Crawl space vents are still a standard out here in the bay area. However, they often bring in as much or more moisture than they let out, depending on the humidity in the crawl space versus outside. Simply closing the vents is not a solution. One needs to have a fully sealed, impermeable vapor barrier down first and then and only then seal off the vents.
Internal Sources
Also, simply having a very well sealed home can lead to moisture build-up, depending on the space per resident, activity of the residents, and the amount of mechanical ventilation. Showers, cooking, laundry, and even breathing all add a little bit of moisture to the air, which, in some cases, can be enough to contribute to crawl space moisture. Ventilation (properly installed bathroom fans, HRV systems etc) is the main solution in this case.

Gas appliances are also a potential humidity concern, if the moisture rich exhaust gases are not venting properly. This is particularly bad, because these gases also contain carbon monoxide (poisonous waste gas), in addition to water vapor. Open combustion gas appliances located in a crawl space, or in the house or basement, can be a significant contributor to humidity.

hygrometerDealing with Moisture Build-up
Humid Climates
Dehumidifiers can be useful in humid climates, such as the southeastern united states. Ideally, these should be used in conjunction with proper sealing and vapor barrier.
Dry Climates
In less humid climates, such as the majority of dry climate California, you shouldn’t need a dehumidifier. Assuming your crawl space is sealed properly from bottom to top with a full vapor barrier and the vents have then also been sealed off (encapsulation), you should be fine without one. If you are particularly concerned for some reason after having your crawl space encapsulated, you can install relative humidity data logger to monitor the temperature and humidity in your crawl space. If there still exists above ideal levels of humidity then you can set up a small exhaust fan that is on a humidistat. So if moisture increases for whatever reason, the fan will kick on until the moisture goes back down. 9 times out of 10, these are not needed.

crawl-space-encapsulation-1Benefits of an Encapsulated Crawl Space
Duct Insulation
If your ducts are in your crawl space, then sealing it will provide the additional benefit of providing extra duct insulation, and protecting them from humidity, pests, etc. This puts the ducts in a partially conditioned space and provides large increases in efficiency to the HVAC system.
Floor Insulation
Also, encapsulated crawl spaces serve as an indirect form of floor insulation. When you have an encapsulated crawlspace you are decreasing the temperature difference between your house and the crawlspace. Effectively, this decreases heat loss through the floor, accomplishing the same thing that floor insulation does, with the added benefits of humidity control and air quality.

Air Quality
Cleaning out and sealing up your crawl space can significantly improve air quality in your home. You will not longer be breathing air that has been exposed to moist soil and potentially mold, rat waste etc. Your crawlspace is now a clean, dry environment.
Lasting Protection
Protecting the inner workings of your home from moisture damage has numerous long-term benefits.

For more information, call (925) 363-4498 or e-mail to speak to a technician, or schedule an energy audit.

Warning! Important tips for crawl space work
Three things to be aware of if you’re doing crawl space work, or having it done (unfortunately, not everyone does their homework).
Appliances: Open draft gas appliances should not be located in a sealed, encapsulated crawl space. An open draft combustion appliance is a common appliance (often ~80% efficiency) that uses oxygen from it’s surroundings to burn the gas. Limited oxygen in an encapsulated crawlspace will interfere with the combustion process, potentially leading to a dangerous situation, humidity buildup or carbon monoxide buildup. If your HVAC unit or water heater is, or will be located in your crawl space, it needs to either be a sealed combustion unit (90% efficiency unit or higher) or an electric heat pump unit that burns no gas to begin with.

Materials: Vapor barrier should be 15-20mm polyethylene plastic barrier rated to come in continuous contact with moist soil.
Prioritize: Each layer of plastic should sheeting should be fully sealed to each adjacent sheet, up the pier blocks, and up the perimeter foundation walls. Once the vapor barrier is properly installed, then and only then should the crawlspace vents be sealed off. If you seal the vents without the vapor barrier you will be potentially trapping moisture down there that is coming from the soil or home.

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