Crawl Space Insulation Installation Question

[Robert L. Bassett]

I recently inspected a crawl space which had the insulation's vapor barrier face down rather that with the vapor barrier up against the home's wooden floor. The installer told the homeowner that this was the correct way to install it, however, my manuals state the vapor barrier should be to the floor. Am I correct or is putting the vapor barrier either way acceptable in South Florida because of its exceptionally warm, humid climate?
Thank you in advance for you help.

[Billy Boerner]

Found on NACHI... Hope this helps.

P.S. The crawl space addition with the problems also had the insulation installed wrong, with the vapor barrier on the bottom and the batts tabs stapled to the joist bottoms. A common mistake homeowners make when adding insulation to crawl spaces.

Insulation should always be installed with the vapor barrier on the "warm in winter side" ... otherwise it can trap moisture in the joist spaces.

That, with the other conditions, was a red flag to peel back some insulation and probe the wood. I wasn't to surprised when my awl went completely through the bottom parts of the framing members.

Also, here is a link to a pretty good discussion on crawl space ventilation ... http://www.eere.energy.gov/consumer/.../mytopic=11480

[Marcel R. Cyr]

Originally Posted by rbassett

I recently inspected a crawl space which had the insulation's vapor barrier face down rather that with the vapor barrier up against the home's wooden floor. The installer told the homeowner that this was the correct way to install it, however, my manuals state the vapor barrier should be to the floor. Am I correct or is putting the vapor barrier either way acceptable in South Florida because of its exceptionally warm, humid climate?
Thank you in advance for you help.

Welcome to the MB Robert.

If this is a Florida location, that might be right.

Vapor retarders should be used in most parts of the country. In colder climates, place the vapor retarder on the warm side--the lived-in side--of the space to be insulated. This location prevents the moisture in the warm indoor air from reaching the insulation.


If you live in an area where the climate is hot and humid the process is in reverse. As the humid outdoor air enters the walls to find cooler wall cavities it condenses into liquid water. Placing the vapor retarder on the outside will reduce water vapor movement from the outside from getting into the building envelope. Any vapor that does get into the walls or roof assembly can evaporate to the inside and therefore dry out before the moisture can lead to mold, mildew and rot problems.

There are also different provisions for vented and un-vented and insulated Crawlspaces.

Hope this helps a bit.

[Joe Funderburk, CMI]

I don't know about Florida. But here, in SC, it would be wrong.

"Floor insulation has been installed up-side down. The vapor barrier should be installed against the sub-floor. Service to reverse the insulation is recommended. And since the improper installation of insulation can trap moisture against the floor framing and may result in decay, the floor structure should be thoroughly evaluated by a licensed contractor."

[John Shishilla]

I would call it right in Central and South Florida. I am not sure about the North end.

[Marcel R. Cyr]

Originally Posted by jfunderburk

I don't know about Florida. But here, in SC, it would be wrong.

"Floor insulation has been installed up-side down. The vapor barrier should be installed against the sub-floor. Service to reverse the insulation is recommended. And since the improper installation of insulation can trap moisture against the floor framing and may result in decay, the floor structure should be thoroughly evaluated by a licensed contractor."

Hi. Joe,

I think you are in an area stuck between to sheets.
The Cold and the Hot and Humid.

Position of the Vapor Barrier

The vapor barrier should always be placed on the high
(humidity) vapor pressure side of the exterior wall.

This is the exterior side for buildings in the south and the interior
side for buildings in the north.

For buildings geographically located in areas where
the indoor and outdoor vapor pressures are nearly
equal, there is no need for a vapor barrier as the
concentration of water vapor in the construction
cavities will eventually reach the indoor and outdoor
humidity conditions.

However, if the day/night cycle of the area causes a significant difference in temperature between one side and the other or if a masonry
cladding is wetted and solar heated frequently, it may
be prudent to install a vapor barrier on the side of the wall cavity or insulation which is wetted most frequently while ensuring that rain penetration moisture does not become trapped in a cavity with vapor barriers on both sides or without drainage openings.

[Christopher Currins]

Originally Posted by rbassett

I recently inspected a crawl space which had the insulation's vapor barrier face down rather that with the vapor barrier up against the home's wooden floor. The installer told the homeowner that this was the correct way to install it, however, my manuals state the vapor barrier should be to the floor. Am I correct or is putting the vapor barrier either way acceptable in South Florida because of its exceptionally warm, humid climate?
Thank you in advance for you help.

The installer is correct.

[John Shishilla]

Originally Posted by ccurrins

The installer is correct.

Thanks!!!!!!!!!!!!!