2″ x 6″ construction in a Maine cabin but Owens Corning insulation R-19 is 6 1/4″ thick. Crushing it down to 5 1/2″ looses 1 R factor. R-21 is made for 2 x 6 with a 5 1/2″ thickness but you can’t find R-21 anywhere.
How can 5 1/2″ = R-21 while 6 1/4″ = R-19 ? Does the loss of 3 R factors mean that much. I would think that every R factor I can gain for my Maine property is going to be worth it.
Thanks,
Chuck
Replies
R you sure you want to open this can of worms?
R factor is important, but not nearly as important as getting a tight envelope. Obsess on sealing air leaks and don't worry quite so much about R factor.
(Expect any minute to be told that you're a fool to use fiberglass instead of 1) cellulose, 2) sprayed foam, 3) rigid foam on the outside, 4) ICFs, or 5) SIPs. And I'm sure I left out a few.)
Thanks Dan,
I guess I will be expecting a "fool" comment soon, as I do plan on using fiberglass. The cabin is totally wrapped and taped. Foamed around all doors and windows. Insulated and wrapped under the cabin. Ridge vented with R-38 in the cathedral ceilings.
I am a legalized booky and with my 2 college sons (architectural design and computer science) we are building ourselves (with A LOT of help from various sources). 4 years into it now and 37 miles away from the closest lumber/outlet store so we carry in as much as we can each trip.
Thanks again
Chuck
I think it's worth ordering the R-21 batts
but I can't answer the question as to why R-21 "high density" performs better than 6" R-19 squashed down to 5 1/2"
And I really don't understand why R-19 in a open sided floor assembly performs at R-18 if fit snugly into a 5 1/2" wall cavity that's air sealed on all sides.
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"You cannot work hard enough to make up for a sloppy estimate."