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insulating with styrofoam

sawdustmaker49's picture

i'm about to start a rehab of a rental properity i own. the dwelling was built in the 70's. it has a std. 2x4 walls with black celotex and 5/8" ceder siding on the outside. the vapor barrior is plastic under the drywall.  i want to cover the outsidewith 2" of stryofoam and add vinyl siding. i've read about plastic vapor barriors causing problems. should i remove the plastic if i add the stryofoam?

Critical data missing:  (post #206630, reply #1 of 2)

Critical data missing:  Where?


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

You (post #206630, reply #2 of 2)

probably should. If you have minor water leakage issues at some point down the road, it will work out better if the walls can dry to the inside. If you have moisture migrating into the walls from the interior... same thing... more drying potential is good. Most vapor movement is by air, not diffusion.

Likelihood of problems really depends on occupant habits and building conditions. Wet crawl space, basement, or slab will result in more interior humidity and higher risk. Lots of occupants who cook a lot and never use the bath fans, higher risk. Two houses on adjacent lots could have entirely different outcomes depending on the individual circumstances.