Home>Discussions>INSULATION & HVAC>Insulating the floor above a crawl space
4 posts / 0 new
Last post
Insulating the floor above a crawl space


I've read some of the other threads posted on this topic, but none have quite addressed my situation.

The previous owner had installed R-13 insulation in the ceiling of the crawl space with the vapor barrier facing towards the crawl space floor. I need to add insulation to a few areas and also want to replace some where the paper backing has gotten mold on it. Should the vapor barrier be facing towards the crawl space floor or towards the living space above?

FYI, I am also addressing an ongoing moisture issue in the area. It generally stays dry, except when we get heavy rain storms from the NE. I run a dehumidifier, but need to have the back rubble stone wall re-pointed and maybe add a sump pump.


Re: Insulating the floor above a crawl space

ARK .... when referring to the ceiling of the crawl space that would be the under side of the floor ... i believe that's what you meant?

Vapor barrier should be on the warm side of the insulation. So if the floor is warmer than the crawl space the vapor barrier should be toward the floor before the insulation.
Covering the insulation with plastic on the bottom side will trap moisture in the fiberglass bats and have two negative effects :

  1. reduce the insulation properties of the fiberglass bats
  2. encourage mold and possible wood rot

If the floor of the crawl space is dirt then it would help to cover it with a 6 mil plastic. This will help with moisture migrating from the soil into the crawl space.
Hope this helps.:)

Re: Insulating the floor above a crawl space


Based on your reply, the existing insulation was not installed properly in my crawl space, which is what I suspected. One follow-up question. Since, I really don't want to make a big project of taking down the existing insulation and re-doing it the correct way (vapor barrier next to the floor of the heated living area above), would the next best thing be to simply slit the paper facing on the existing insulation?


Re: Insulating the floor above a crawl space

ARK ... the choice is yours .

Personaly I would turn the insulation around so the paper backing is toward the floor. Cutting slits in the backing may or may not help with the current situation ... I can't say for sure since never have or never would do this myself, though my guess would be minimal advantage.

Another suggestion would be to replace the plastic that's currently covering the insulation with house wrap. This will provide an air barrier but allowing the insulation to breath and helping to allow any moisture that will be present to escape.

Hope this helps and good luck.:)

Sponsored Stories

TV Listings

Find TV listings for This Old House and Ask This Old House in your area.