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Correct way for insulation to be installed in attic with cross braces

CRF_GBA | Posted in Energy Efficiency and Durability on

I have a 3 story townhouse built in the mid-80s in Maryland just outside of Washington, DC (zone 4A Mixed-Humid). I have just started air sealing my attic (discovered a number of big holes in attic floor), when I discovered what I think is the wrong method of insulating the attic. Most of the attic was insulated using R-11 faced fiberglass batts, and then 5 inches of blown fiberglass insulation (I guess this was done this way to get a vapor barrier). I think that my townhouse was built in modules and then assembled on site, I found what I think are the lifting straps still attached to the top plate when I sealed it.

The problem is that in many areas, the batts are stapled to the rafters 1 to 2 inches above the ceiling drywall. Because it was built from modules, there are a number of 2×4, 2×6 and even 2×8 cross braces that run flat to the ceiling between the roof rafters and some that run parallel to the rafters. It seem wrong to me having the batts stapled above the ceiling, and I think that the batts should lie flat to the attic drywall but the cross braces will cause voids in the contact of the fiberglass batts in those areas.

I guess that my first question is should I go though the entire attic and un-stapled all the fiberglass batts were I find it stapled.

Second question, in those areas where there are cross braces, would I be better off pulling up the fiberglass batts, allowing the blown fiberglass to fall to the ceiling, remove the kraft facing from the fiberglass batts and then stick the defaced fiberglass batts on top of the blown fiberglass (since I don’t really require a vapor barrier in my area)?

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  1. GBA Editor
    Martin Holladay | | #1

    You are correct that your insulation should be resting on your drywall, without any intervening air gap. The best way to proceed is to remove all of the insulation from each truss bay (or joist bay), one bay at a time, so that the ceiling can be inspected for air leaks. Once the air leaks have been sealed, you can then fill the bays with insulation -- either replacing the fiberglass batts (installing them against the drywall), followed by loose insulation, or else getting rid of the fiberglass batts and installing 100% loose insulation.

    In either case, the kraft facing on the fiberglass is irrelevant. You can leave it there if you want, or omit it.

    Once you've done all of the above work, you could finish off the job by installing 6 or 12 inches of cellulose on top of everything. The cellulose cap will go a long way to preventing convection currents from reducing the performance of your insulation layer.

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