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Question of the Day - #92 Cavity or entire wall?

PostPosted: Tue Dec 02, 2014 8:48 am
by RDavidson
2015 MN Rules section 1322.0402, subpart 1, contains a table listing the insulation and fenestration requirements by component. The required R-value for a wood frame wall is 21. A residential designer calls with a question about this requirement. Does the R-21 apply to the cavity insulation or to the overall R-value of the wall? She says commonly purchased batt insulation for 2x6 wall construction has an R-value of 19. What do you think? When the ceiling R-value is listed at 49, is this the value of the insulation of the assembly?

The same table in the IECC that is replaced by this amendment contains a footnote that explains that the number is cavity insulation, not the wall assembly. Would it have been helpful to have this explanation in the Minnesota rules? R-21 batts are manufactured and available.

Re: Question of the Day - #92 Cavity or entire wall?

PostPosted: Thu Dec 04, 2014 10:08 am
by RDavidson
Update, update, update! We have a correction. If you go to page 541 of the Minnesota State Register you will find a correction to the question of cavity insulation. I'm sure many of you read the Register every week so this doesn't come as a surprise. The rule has changed for those of us in the banana belt of Southern Minnesota. We can now comply with an R-20 cavity insulation while those in the tundra must have R-21. There is a new footnote that addresses the question of continuous insulation which is now necessary because, as an alternate, only in the banana belt we have the option of R-13 cavity insulation and R-5 continuous insulation. Not sure why the folks up north don't have that option but..... There you have it.