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Gary Myers
Posted: Mar 27, 2011 12:16 AM
insulating crawlspace walls?
Hey guy's, I have been spraying a lot of crawlspace walls and the odd time just the under side of the floor. Which is more effective to keep the room insulated....the crawlspace walls or the underside of the floor??
Posted: Mar 27, 2011 09:17 AM
There are a lot of ways to attack a crawl space. It is best to conduct a hygrothermal modeling study on both ways. check out the humidity and temperature in space. Is it totally enclosed or open to the outside? Does it have concrete or dirt floor? Are the foundation walls below grade or is above ground? If below grade, is there a drainage tile system to keep water out of the floor? Are the foundation walls water or damp proofed? How high is the water table?

All of these factors must be identified and addressed before continuing.

If you have a dirt floor and open sides, I like to spray to the underside of the floor of the inhabited space. This effectively isolates the interior space from the outside space, both in temperature and humidity. Also, keeps insects, critters and varmints out of the house.

If the crawlspace is totally enclosed with masonry foundation walls and the floor has a vapor retarder on it and other moisture producing factors have been addressed then you can spray the walls of the space to make the space "semi-conditioned".

There are some good articles on basements and crawl spaces at buildingscience.com. Check them out
Posted: Mar 27, 2011 09:40 AM
...many bs geru's (that's building science) look at the enclosed crawls as pigmy basements,,,the cement fellas just forgot to set the tall wall forms,,,
shoot the sides and the box sills and rim joists as you would any other basement,,,

consider having your freindly hvac peep add a duct to the space to further condition,,read this as warm floors,,,but many of these spaces will do just fine without,,,conduction,,convection,,radiant,,i think it goes,,,
and as a sidebar,,ah,,the old dirt floor,,,double-ahh,,,with the lovely polysheet for vb control..cut real nice around the,,lets say chimney,,columns,,or not,,but taped real perty to the sidewalls,,,
why not consider,,lets say 2" closed cell foam down on grade for both thermal and vapor control??? side to side seamless,,,moisture vapor control,,,soil borne gases control(radon),,,ties right into the sidewall system,,,
just be sure you are applying a closed cell foam
that has paper that shows it is allowed exposed
in attics and crawls entry service for utilities only,,,not sure,,ask your supplier for the documentation,,he will have it if he has it,,,
oh baby is this space conditioned now...
insulation=the isolation of 1 environment from the other....
kinda like the rational to the conditioned lid assembly,,,identifying the buiding envelope where it belongs,,,around the entire exterior of the structure,,,
consider,,,lets build a home,,,and then put/design/encourage a 140 degree hot house on top of it,,,while we are trying to maintain a 75 degree comfort inside,,,watch the meter whirl... brilliant,,,
oh yeah crawl spaces,,,more coffee pleez :)
Gary Myers
Posted: Mar 27, 2011 02:28 PM
Hey, you guy's are right in that there are lots a variables to consider in a crawlspace. The majority of the ones I have done have a dirt floor and have only a small entrance and maybe a couple of vent holes. I usually put down 6 mil poly on the dirt floor and seal it when doing the walls. Thanks again for the info.

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