1 or 2″ xp foam does it make that much of a difference
im renovating my slabed ranch in mass, Im replacing 50 year old fiberglass (poorley installed) w/ dense pack cellulose, in 2×4 walls. giving a perposed R value of 12, after 3/8 plywood sheething, i was going to install 2″ xp foam w/taped seems. I figure using this will allow moisture to move threw it. and then side it with vynil shake. does the 2 inch vrs the 1″ xp really make that much of a difference?? besides the R5 value.(trying to achieve airsealing.)
does anyone know any good sites for a first timer with vynil shake. ive done tons of wooden shake. perfect and hand split. not to familuar with vynil any suggestions would be great, thanks
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I think you may be confused about this whole matter a little bit..a properly"airsealed" wall/roof will NOT let moisture travel through it. and, believe it or not, XPS is permiable. If you were going to aiseal with the use of any foam, the place to do it would be right at your vapor barrier, which in your area of the country is on the inside, right?Either way, you'd want to use use a foil faced Poly-iso product such as Thermax or R-Max. If your vapor barrier is in fact on the outside of your home I'd use the poly-iso 2" with taped seams and penetrations. Otherwise, airseal on the inside with silicon and use the XPS untaped on the outside for added R value. and I guess to answer your actual question about "does thickness make a difference" not unless your considering r-values.
theres so many discussions about the foam, with or without foil face. I think that answered my questioned, whats ur take on dense pack cellulose vrs craft face r13 in the walls. a friend of mine who is a remodeler said you can dense pack the bay without removeing the fiberglass but ive heard that if i have the outside open just take the lower sheething off and then pull everything out. i dont see the real benifite of removing the old stuff except for the paper face for a vapor barrier. if i striped it all out i would loose the vapor barrier? im confused on this topic, i usually do new construction and we've alwaysed used fiberglass and spray foam. what is your take ?
I wouldn't reccomend trying to un-install/abate the old kraft FG bats, or dense pack ontop of them for that matter..In the past at homes with a bad seal(no or improper VB) we would remove all the old sheetrock/wall paneling,strap 2" poly-iso to the inside of the wall, tape the seams, and sheetrock over the topand we would see outstanding results, as far as air leakage, with the help of our trusty blower door. Plus you get the added bonus of near R-14. In my opinion that's less work than attacking from the exterior. But that's just me, I don't mind sheetyock work.
But what ever you do, don't forget that air comes in from the bottom(floor) and leaves through the top(cieling) not to say that properly sealed walls won't help, but your time and money is better spent in the attic and crawlspace.(you have a slab home so just make sure that the seal around the bottom plate is skookum.)
You're confusing me.
Your first statement is that "a properly airsealed wall/roof will NOT let moisture travel through it" and then your second is that "XPS is permiable" (sic). The second one is actually true, because XPS is vapor permeable although I think it's going to substantially reduce the ability of a wall to dry to the exterior if it's installed on the exterior. Foil-faced polyiso is much more susceptible to moisture damage so I'd think twice about using it as exterior insulation unless you're absolutely certain of your ability to keep it dry forever. In the OP's case a nice wall assembly would probably be 2" of XPS over the sheathing, with a rain screen detail behind the siding. Not sure how cold it is in his area, so he should investigate the needed R value of "outsulation" before choosing. Taping the XPS, or using Tyvek over the sheathing should provide a good air barrier.
thanks for the info, i was told that in the north east that, a big contributer was the airsealing qualities of a wall correct? the drying of the wall is very important and that was a big concern of mine. nowintg the r-value had to be greater beond the sheathing than the wall its self. so the condisation doesnt happen at the sheathing. for the cellulose being installed in place of the fiberglass, I took it as a better and more effecient isulation, not having to worry about "holding the warmth" not only that university of amherst and a couple repitable site have done extensive research on the conductive quailities of cellulose vrs fiberglass, i went on the assumption that there finding were correct. as for the vapor barrier, They say the wall needs to breath in or out so i figure this would allow it to breath to the inside and xp it perm. and i figured that it would also breathe goint toward the outs side. Correct me if im wrong but i couldnt see all the resources tha i have found to be wrong?? thanks for the info and hine sight.
huh?(and sorry about the spelling error)
I really don't think that you would want a tight air barrier on the outside of the wall if your vapor barrier is on the inside so that it could dry in the unlikely event that it does get wet inside of the wall cavity. As far as your confusion, are either of the "confusing statements" false? and if so, how? If you were to use poly-iso, than yes, you would want to make damn sure that it stays dry, and that my friend is what you always try to do in any given situation, regardless of what type of material you are using(in the matter of outsulation atleast)
Furthermore, if in fact his VB was to be installed on the outside of the wall, why would you suggest XPS directly after aknowledging the fact that it does infact allow moisture through?
your confusion is confusing me...good day sir.