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Jack
condo insulation

my daughter's condo is under insulated! There is about 3 inches of rock wool in the attic (2x6 joists). I want to add insulation. Should I just add 9-12 inches across the joists and leave the 3 inch air gap underneath. I can't find a 3 1/2 inch thick unfaced roll to fill this gap. I really want to cover the wood rafters with insulation. Or should I not even worry about the joists and just lay in 9 1/2 inch batts in between them. I don't know that much about blown in insulation but this seems to be an alternative although I would prefer rolls or batts. The attic is more than full height and appears to be easy to get to the eaves to staple in the foam baffles to do it right. Any suggestions? Thanks in advance.

MLB Construction
Re: condo insulation

the easiest and best way is to have insulation blown in. if you opt to do it yourself, you can get 3-1/2" unfaced batts, i know home depot sells them, i get them alot and just bought some a week ago. so, fill up the rafter bay with the 3-1/2" then get some R-30 unfaced and lay them the opposite direction. pretty simple, just remember not to leave an air gap between the two layers of insulation.

Jack
Re: condo insulation

Thank you MLB Construction. I couldn't find the 3 1/2" unfaced insulation down here in Ct. So I tried up in the Worcester area where the condo is located and you are spot on. Home depot does have it in stock there. I will be doing it this weekend.

Thanks again,

Jackl23:)

keith3267
Re: condo insulation

I know that the usual practice is to layer the second layer of insulation perpendicular to the joists, but I really don't think that is the best way. when you do this, you create a potential chimney for heat loss at every intersection of the two layers. I would put the top layer in the same direction, but offset by 1/2 the width of the insulation. A cross section view of this would be like a brick layup.

The center of the top layer would be directly over the joist with the seams between batts at the center between the joists. There would be no heat pipes where the edges of the batts on the top layer cross over the edges of the batts on the lower layer.

jkirk
Re: condo insulation

by doing it caseys way you span over top of the raftes or bottom chords of the trusses. this makes for a better job and reduces the chance of the second layer weighing down the first causing it to compress in turn reducing r value

keith3267
Re: condo insulation

Doing it my way also joists and does not compress the insulation in the lower layer. It does not work as well for trusses though.

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