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What is the best method of getting r-30 in a 2X8 cavity?
Bibs, or rigid? Can you even use bibs in roof/ceiling? What is the avg. u per inch of each insulation type?
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Replies
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Look at archives re insulating with rigid foam (EPS, XPS), polyurethane
(PUR), and loose materials such as cellulose, wet-spray cellulose, BIBS, etc.
The loose materials, icynene, and regular fg are around R3.5/", hi-density fg
a little more, the foams R4.5/" to R7/" (PUR). If you're determined to get R30
you'll need just over R4/", or foam added above or below, or furring, or any of
a variety of other techniques. 2x8 is not shallow -- we have 2x6's, some have
2x4's.
I mention these because you will find so MUCH in the archives, too much to
summarize. More important than the precise R-value is the quality of the
installation, e.g. the number of flaws such as air leaks, thermal bridges
(rafters), etc. Oh yeah, and cost relative to payback!
*To summarize - vent or not - that is a different argument. "Skim Coat" the underside of the roof/rfaters/baffles with PUR and dense packt he rest.Yes you can use a bibs type application in a roof. It just billows down and looks odd - no big deal. Many new houses are being done this way.If you stop heat movement by convection and radiation, the last part - conduction - makes almost no difference. R value only measures conduction. Convection and radiation are the biggest culprits in a roof/ceiling.-Rob
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What is the best method of getting r-30 in a 2X8 cavity?
Bibs, or rigid? Can you even use bibs in roof/ceiling? What is the avg. u per inch of each insulation type?