batt insulation over blown-in


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Old 06-21-23, 11:24 AM
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batt insulation over blown-in

Everything in my old house (built by the original owner) is funky. My goal is to add insulation to the attic which currently has old blown-in stuff which has compressed significantly. I cannot add insulation between the roof rafters because they are set on random spacing (24.75" 22.5" 23" etc.). And guess what? The ceiling joists are done the same way. My plan is to use un-faced fiberglass batts or rolls of R-30 laid on top of and perpendicular to the ceiling joists but in some places that will leave an air gap between the old blown-in and the new stuff. (Please see drawing below.) Is that a problem? Or possibly a benefit? I am grateful for your thoughts.

 
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Old 06-21-23, 01:09 PM
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This is not a problem. Just use more blown in insulation, either blown fiberglass or cellulose. Trying to use batts is creating the problem.

If you have any soffit ventilation you will need to add chutes first in order to maintain an air space into the soffit and below the roof deck.
 
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Old 06-21-23, 01:47 PM
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Creating which problem?
 
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Old 06-21-23, 04:56 PM
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i cannot add insulation..... the ceiling joists are done the same way. ......... In some places that will leave an air gap between the old blown-in and the new stuff.
.
 
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Old 06-22-23, 06:13 AM
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If doing blown in and your DIY it is a pretty easy, one person to feed the bails another to handle the hose, Much easier than hauling all that insulation up into the attic, crawling around, cutting and trimming around all the trusses.
 
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Old 06-22-23, 07:15 AM
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I would think laying unfaced bats perpendicular to the attic floor joists would give at least two benefits. They would provide a greater total combined R value as well as insulating directly above the wood joists.
 
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Old 06-22-23, 10:56 AM
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I just had cellulose insulation blown into an attic and I wouldn't do it any other way. The whole project was done in about 2 hours and wasn't all that expensive. I had a company do it, but even as a DIY project, I'd much rather drag a hose around than fight with insulation batts.

As stated, be sure you have ventilation figured out in terms of soffit and upper vents.
 
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Old 06-22-23, 07:23 PM
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I would think laying unfaced bats perpendicular to the attic floor joists would give at least two benefits. They would provide a greater total combined R value as well as insulating directly above the wood joists.
That might be true IF the bats are tightly installed without ANY gaps. The chance of doing this type of install is next to zero.
 
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Old 06-23-23, 12:28 PM
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The new blown in insulation also provides a better air sealing, especially the cellulose, than you would get from bats!
 
 

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