Here’s my situation. I have an unfinished basement in a 2 story home with a 2×6 wall in the basement that faces to the west and is fully exposed from top to bottom on the exterior of the home. The wall has r19 fiberglass bats of insulation along with a poly vapor barrier on the inside of the home. The sheathing is 3/4 buildrite with hardboard lap siding painted dark red. In the summer time with the central a/c running and temps around 90 with high dew points, moisture forms between the poly and the insulation. My understanding is that when the hot and humid outside air comes through the wall and cools to the dewpoint temp it then condenses. My question is how do I prevent this from happening? With a higher r value insulation in the wall wouldn’t the air still condense at some point. Any help would be very much appreciated.
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In summer, you have a wrong-side vapor barrier. You do not mention where you are located, or whether you have a significant heating season. Regardless, unless you are in the cold sections of Canada, which is unlikely, your wall will perform better if you remove the poly. If you want to include an interior air barrier (and you probably should, since it will improve the energy performance of the wall), install interior drywall.
I live in minnesota and if the vapor barrier were removed frost would form inside the wall cavity on the sheathing in the winter time. Installing sheetrock would only hide the fact that there is condensation inside the wall, right?
Whether or not you have a vapor barrier will have little effect on whether or not you have condensation inside your wall during the winter. The most important mechanism for introducing interior moisture into a cold wall cavity during the winter is via the transport of air. This has absolutely nothing to do with vapor diffusion, which is a minor moisture transport mechanism in most cases. Stop the interior air from migrating into the joist spaces, and you will prevent the winter condensation you fear. That's why a carefully installed air barrier (drywall) is more important than poly.
there is no such thing as a carefully installed drywall air diffuser in a basement... gimme another solution that sounds like real-worldMike Smith Rhode Island : Design / Build / Repair / Restore
This might definitely help - http://www.buildingscience.com
Regards,
Eric S.
as some of the others have said.. during the summer , the system reverses..
Building Science uses foam to defeat this.. ( see the site )... but if you use a stud wall.. then you need two vapor barriers.. one against the concrete wall..
and one on the warm side of the stud/insulated wall.
if we are buildinga stud wall.. we drape 6 mil poly and fasten it to the sill, drape it dwon the wall and BEHIND the slab so it will lead any condensate into the stone we alway sput under our slabs..
if you haven't done this then drape it down the wall and onto the slab and under your stud-wall shoe ( which is usually PT )... then build and insulate your stud wall and apply another 6 mil vapor barrier to the warm side.. this in effect encapsulates your wall...
now .. no condensate behind the wall.. since there is no condensing surface ( the poly will not be colder than the concrete )... and no condensate inside the wall because it was stopped as a vapor on the warm side...
for the last two years or so , we've been using EPS foam with Performguard borates bonded with either OSB , or Blueboard (gypsum )... the osb is great for unfinsihed basements , you can fasten things directly to it...
Mike Smith Rhode Island : Design / Build / Repair / Restore
Building Science uses foam to defeat this.. ( see the site )... but if you use a stud wall.. then you need two vapor barriers.. one against the concrete wall..
Where is a concrete wall mentioned?
I read the 2x6 wall is the exterior wall. It has r-19 fg insulation with an interior poly barrier. So exactly where are you putting this new poly barrier?Between the existing sheathing and studs?
I read this to be a frame wall as well. I'm thinking ridgid foam over the face of the studs, seams taped. That way the backside of the foam will stay relatively warm, and not get to the dewpoint. Vice-versa in winter. Also, a color other than red on a west-facing wall would slow the sun-drivin moisture. Maybe white would help.
Steve
hmmmmmm... could it be that i read it wrong.... i can't find his concrete wall either..sorry 'bout that
so ... lose the vapor barrier and blow the wall with dens-pak cells... then foggedabouditMike Smith Rhode Island : Design / Build / Repair / Restore
There is only a stud wall and no concrete. What are dens pack cells and what advantage do they have over my present system?
cellulose insulation can absorb and release moisture without condensing..
when it is blown in at higher than normal density ( higher than 2.0 lb/cf ) thye call it dens-pak...
in our wall systems we blow it at about 4 lb/cf
the dens-pak itself becomes an air diffuser and will not allow the same moisture bearing air currents to move thru it that fibberglass insulation will..Mike Smith Rhode Island : Design / Build / Repair / Restore
Is the vapor barrier installed and then the insulation would be blown in from the top with the plastic pulled back? Can this be done with a rented blower?
with dens-pak , in your situation... don't use a vapor barrier.. just blow the cells thru the sheetrock and patch the holesMike Smith Rhode Island : Design / Build / Repair / Restore
I think itt would be better in your climate to have the vapor barrier on the outside of the insulation. Hard to accomplish at this time, I realize.