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Can a DIYer install batt insulation to a Grade I level?

SteveR_79 | Posted in Energy Efficiency and Durability on

Martin Holladay’s article, “Installing Insulation Right – It’s Hard to do a Perfect Job” had me wondering if a DIYer could install fiberglass insulation “right”. Assuming a DIYer were inclined to install it right, is there any reason why they couldn’t install it to a Grade I level?

Also, in this same article is the following sentence:

“To achieve the R-value shown on its label, a fiberglass batt must be installed perfectly in a wall or ceiling cavity enclosed by a six-sided air barrier.”

What exactly makes a wall cavity a “six sided air barrier”? Should each cavity have sealant at all twelve edges of the six sides? I’m remodeling and will be removing the drywall on most if not all of the exterior walls. Now would be the time to seal the four edges where the exterior sheathing meets the 2x4s and the four edges where the 2×4 wall studs meet the top and bottom plates. Then when the drywall is installed, does it need to be sealed at each cavity even though the airtight drywall approach only shows seals at the drywall perimeter?

I’m only trying to understand how a DIYer can install fiberglass insulation properly and implement the airtight drywall approach as described in Martin Holladay’s article “Airtight Drywall”.

In case it matters:
1300 sq. ft. single story house built in 1960
Zone 3
Wall detail: solid brick veneer, 1/2″ asphalt impregnated sheathing, 2×4 @ 16 o.c., 1/2″ drywall, no insulation
R30 batt plus blown in ceiling
R19 batts in floors
Vented crawl space with 6 mil poly on ground and gas furnace

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  1. user-723121 | | #1


    I say anyone can install fiberglass batts correctly if they are committed to doing a good job. The fiberglass batt must completely fill the space between the studs. Contact should be made between the batt and the studs, top and bottom plate, the exterior sheathing and the interior surface be it drywall or other.

  2. davidmeiland | | #2

    It's easy to install fiberglass in regular stud bays that have no obstructions. The insulation is the perfect width... what's not to like?

    It gets a lot harder as soon as there is pipe or wire or anything else in the way. Suddenly you have to measure, cut, and shape this floppy, uncooperative, and generally unpleasant material and it gets tempting to start rushing, stuffing it in or leaving gaps instead of doing it right. Installing insulation is a lot like finish carpentry, you have to really take your time and cut every piece correctly.

  3. jklingel | | #3

    " have to really take your time and cut every piece correctly." And, you have to get batts that are made exactly alike. I have not touched that stuff in several years, and only on 4 or 5 houses, but I never seem to get a large quantity without several "weird" batts; thin, knotted up in places, won't fluff out at all, etc. Follow that with warped studs, and you have a sub-par wall. Maybe the stuff is better now. ???? I wonder if cellulose, cotton, rock wool, etc, has better quality control, or is cut a tad fat so that it accommodates small irregularities better (and, I believe, they all have a slightly higher R). Besides, why fight the itchies?

  4. SteveR_79 | | #4

    Thanks for the input. I have every incentive to do it correctly since it is my home. It does take time to cut out around wires and pipes but it's just work. As long as I'm not missing some key point, I'll deal with the work.

    John, fiberglass batt was my only consideration, since that is what is available at the big box stores. I'll check if there are any other batt options. Initially I considered dense packed cellulose to deal with the warped studs, etc. But I couldn't find a proper insulation blower for rent and I wanted to keep this as a DIY project.

    Is there any new input on what constitutes a six sided air barrier for batt insulation? See the paragraph entitled "If you have a good air barrier, how much air moves through your insulation?" in Martin Holladay's blog one year ago:

  5. davidmeiland | | #5

    A good insulation sub is worth the money they charge. I would only install batts if you can't possibly afford blown cellulose done by a pro.

  6. GBA Editor
    Martin Holladay | | #6

    A six-sided air barrier means that each stud bay or joist bay shouldn't have leaks on any of the six sides. Most fiberglass-insulated stud bays or joist bays are leaky.

    Think through your air barrier details. Addressing penetrations is key; so is choosing airtight electrical boxes, and sealing those boxes carefully.

    Obviously kneewalls facing an attic space must be enclosed on the rear with Thermoply, drywall, or rigid foam.

  7. SteveR_79 | | #7

    David, Finding a "good" insulation sub is one of my worries. It can be done but it takes time to do it properly. Instead I would rather invest that time in learing how to operate a blower to install dense packed cellulose. But since I can't find a blower to rent (yet), it's a moot point. Also since I'm living in the house, I would like to insulate in stages as the remodeling progresses. At a local energy fair, I asked an insulation contractor about this approach. There would be a trip charge each time they came to my house. That is fair but it doesn't make economic sense for me. I'm still researching other insulation contractors.

    Martin, Thanks for your input. With the drywall removed, all eight edges of the stud bay will be sealed/caulked as well as any penetrations through the studs and plates. My understanding is the airtight drywall approach only requires sealing at the perimeter of the drywall. For a six sided air barrier, should each stud also be sealed to the drywall?

  8. GBA Editor
    Martin Holladay | | #8

    As long as you are following ADA recommendations, you should be OK. Here's more information on airtight drywall:

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