What Goes Into Sealing a Crawlspace?

Last week I discussed why to seal a crawlspace, so how about now looking at what goes into properly sealing the space? There are a large number of variations on how a sealed crawlspace is installed; while most just vary by quality, not all of them are proper. A sealed crawlspace is intended to provide 5 things:

1. Moisture management
2. Pest control
3. Combustion safety
4. Fire safety
5. Radon safety

There are a few items that are required to make sure your crawlspace is properly sealed and that you will get all the benefits that are intended:

1. Installation of a vapor barrier with sealed joints on the floor, piers, and foundation walls.
A minimum of a 6-mil vapor barrier should be installed, with all joints sealed via mastic or an approved tape. It is highly recommended that a higher mil plastic be used because the 6 mil will tend to tear and wear easier.

2. Seal all foundation vents.
No vents or openings to the outside should be present, other than an access door. Porch penetrations should also be sealed with an access panel or permanent material.

3. Provide a foundation drain.
A foundation drain is needed with a backflow preventer. It is a good idea to allow the drain to accept moisture from above and below the vapor barrier.

4. Insulate the floor or foundation wall.
Insulating the foundation wall is more efficient, but either the floor or wall is acceptable. Evaluate the situation and choose accordingly.

5. Air seal duct and floor penetrations.
Air sealing the ducts will help improve your home’s efficiency, and sealing them and the floor penetrations help prevent air transfer between the home and crawlspace. This also helps with fire safety.

6. Vent appliances to the exterior.
Gas appliances should be direct vented or two-pipe vented in the crawlspace. Most vented spaces do not have enough makeup air for single vent appliances, and a sealed one definitely won’t. Direct venting is recommended.

7. Mechanical Moisture Control
There are several variations on this, including the use of HVAC ducts and dehumidifiers. If an HVAC supply duct is to be used, a backdraft damper is needed and no return ducts. This can affect the efficiency of the system, so check with an HVAC contractor prior to doing it. I tend to recommend a dehumidifier, as it is the least problematic.

Additional Item:
A relative humidity monitor is good addition to help you know that the system is operating properly!

Use CFLs!

This is pretty rudimentary when it comes to energy savings, but there are still a lot of people who are not aren’t doing this! Incandescent bulbs convert 90% of their energy to heat and only 10% to light, so they are good heaters but poor light generators. CFLs not only use less energy, but they last longer, too. A 14-watt CFL is equivelent to a 60-watt incandescent. The CFL uses around 75% less energy, and therefore costs 75% less to operate. Also, because the CFL lasts 10x longer, you buy one CFL for every 10 incandescent, which increases your savings. Many will argue that you can’t use a CFL everywhere, but they are also becoming more versatile in their uses. So look at your light use and install CFL’s where you can!

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