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The commentary discussion here that began with bwkwood's desire to "build a cheaper mousetrap" RE: attic ventilation is addressing the short term benefits of such a mousetrap only.
Consideration of the long term cost benefit has not been addressed.
Currently we are experiencing relatively slow energy cost increases but that can not be expected to be a reliable condition for the future.
Energy costs will continue to rise in the future and that fact should be the prime consideration for any discussion regarding insulation and air movement in attic spaces over conditioned living spaces.
The use of sprayed foam insulation ( closed cell polyurethane ) in today's energy conscious world is a no brainer. Sprayed foam insulation addresses all of the concerns raised in the discussion-and its use particularly addresses the overall benefit of cost in terms of future energy savings. Sprayed foam attic insulation is by far the best method of achieving air sealing against the attic space/conditioned space border.
I have not seen any comments posted that directly address the most important concern for maintaining the comfort level in the conditioned space which is air sealing. Sprayed foam insulation is the best way to achieve a maximum air sealing benefit while at the same time providing the highest insulation value available by common insulation methods.
Fiberglass insulation should not be used at all as it does not provide good air sealing characteristics when compared to blown cellulose or sprayed foam insulation.
The attic space will still require proper ventilation if sprayed foam insulation is used.
Getting back to bwkwood's original question about alternative methods of providing baffling over the exterior walls in the attic-this becomes a moot point for consideration with sprayed foam insulation. The very high R value per inch of sprayed foam insulation will mean that there will not need to be a thickness of insulation at the exterior wall area in the attic that will
impede air flow from the soffit until you require around R 70 (using 2 x 6 ceiling joist and rafter widths ).
Don't let the higher per square foot installation costs of sprayed foam insulation deter you from considering its use. Look at the advantages and research the long term cost savings benefits in detail and you will probably see that sprayed foam is the "better mouse trap"!
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