Replies

1. 
   andrew_d | May 12, 2000 06:09pm | #1

   *
   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!

1. 
   Rob_Susz_ | May 13, 2000 04:57am | #2

   *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

2. 
   John_Martin | May 13, 2000 04:57am | #3

   *
   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?