Vapor Barriers in Your Home
Ask Danny, Attics and Basements, Heating and Cooling, Insulation by Danny Lipford
Could you wrap your house with a plastic vapor barrier on the outside before you brick it? If not why, because I’ve heard you can on the inside? I know you can use a Tyvek wrap, so why not plastic? – David
David,
When warm moist air cools, it can become saturated and release some of its water vapor in the form of condensation. If this occurs in the walls of your home, it may lead to the growth of mold or cause wood to rot. Vapor barriers, like plastic sheeting, prevent the passage of both liquid water and water vapor while housewraps, such as Tyvek Homewrap®, stop liquid water but allow water vapor to pass through.
In colder climates a vapor barrier is used on the inside of walls to keep warm moisture laden air from escaping during the winter. Installing a vapor barrier on the outside could cause moisture to become trapped behind it or condense in the walls.
In warm humid climates, the use of a vapor barrier on the inside is not recommended since it could have the opposite effect during the summer when the house is air conditioned. This is not as big a problem as in cold climates, however, since the temperature difference is not nearly as great.
Along the coastal southeastern United States, it is now recommended that a vapor barrier be omitted on the inside and put on the outside, though most builders use housewrap instead. In the middle regions of coastal Southern states, vapor barriers may be omitted completely. Other parts of the country, particularly colder northern states, should install a vapor barrier on inside walls and housewrap outside. Further information, including a map showing the recommendations for vapor barrier use, is available at the U.S. Dept. of Energy website.
Vapor barriers are not considered as important under floors or in ceilings, since attics and crawlspaces are usually vented to the outside which allows condensation to escape without becoming trapped.
5 Comments on “Vapor Barriers in Your Home”
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May 11th, 2008 at 1:56 pm
I have a question on the soil under my house always being moist and damp. I just bought the house, there are no water leaks and there has not been any rain for awhile. The rain runoff does slopes towards the front of house but that does not seem to be the issue right now with no rain. The height under the house is 3 to 4 feet high and there are no water leaks. They installed loose insullation under the house. I would appreciate any info. you have . Thanks Rick
May 20th, 2008 at 5:56 pm
I would be interested in any information as well on this topic.
June 15th, 2008 at 8:19 am
my frend has old brick house small. she has 6,000. heating bill this last winter . there is no insulation in the walls . is there a waw to seal and insulate without loosing space inside home? using tyvek inside ? new insulation that is really thin? was on the sunday show 6-14-18
November 24th, 2008 at 12:52 pm
Have heard recently that insulation (with vapor barrier) should be installed in crawl space with paper against the flooring on the 1st floor. Is this a change in thinking? Have always placed vapor barrier toward crawl space (ground). Also, wondering about installing attic installation between floor joyces? Presently, install attic installation with vaper barrier paper up toward roof boards to allow staples to hold in place. Thanks Loads!!!
July 6th, 2009 at 9:38 am
Hi my question is house was built in the 40’s where there is ship lap in cealings and walls.In the bathroom where there was mold prob. caused from a window in a shower,a majoy no,no,taken all walls out except cieling where some paper is put on the shiplap like wall paper .In the ceiling is blown in insulation ,old stuff ,not all paper is attached is there any thing I should put between this ,more paper for instance between the drywall ,greenboard. There will be a vent fan, installed to vent steam outside ceiling . thanks for listening to stop mold again. Outer wall will have reg. inslation with paper berrior inside warm area…..