Replies

1. GBA Editor
   Martin Holladay | Dec 05, 2011 11:24am | #1

   Don,
   Q. "I found that the [fiberglass] batts are supported between the ceiling joists by friction. Beneath the batts is air space to the ceiling of the closet below. Is this proper construction?"

   A. No. Fiberglass batts require at least one air barrier in direct contact with the insulation; ideally, the batts should be installed in framing bays surrounded by air barriers on all six sides, without any intervening air space between the insulation and the air barrier. This is a requirement of the Energy Star Homes program.

   Q. "What should I do to support the batts?"

   A. Supporting the batts is not the issue. The issue is that the insulation must be in contact with the air barrier. Perhaps you could remove the batts and blow cellulose on the ceiling below. However, that solution assumes that the ceiling is part of an air barrier system; in your house, it might not be.

   Q. "The short length of the bathroom as well as the wall for the stairwell is not sheathed. The bathtub has been installed as though it were in a finished living space; it was butted against the studs, then green board was run from the top of the tub to the ceiling. There is nothing but insulation separating the plumbing end of the tub from the unfinished attic space."

   A. You have correctly concluded that the builder forgot to install an air barrier here. The solution is to install an air barrier around the tub.

   Q. "Is it possible that this construction was to code?"

   A. The 2006 IRC requires "The building thermal envelope shall be durably sealed to limit infiltration. The sealing methods between dissimilar materials shall allow for differential expansion and contraction. The following shall be caulked, gasketed, weatherstripped or otherwise sealed with an air barrier material, suitable film or solid material: ... 6. Knee walls. ... 8. Behind tubs and showers on exterior walls. ..."

   Needless to say, when your house was built in 1998, the relevant code was whatever code had been adopted by your local jurisdiction at that time -- obviously, a code that pre-dated the 2006 IRC which I just quoted.

   Q. "What should I do to fix the problem? I'm considering running ledger strips along the studs from the plate to just above the tub, then installing drywall from the attic side. Fitting around the plumbing will be a challenge."

   A. That would be helpful. If it were my house, I would consider installing something better than fiberglass batts -- perhaps rigid foam in addition to your suggested drywall.

   Q. "For the length of the wall that is not sheathed on the attic side, the insulation batts are stuffed - not stapled - between the studs and are sagging away from the wall. Should I consider sheathing the attic face with OSB?"

   A. OSB would work, or drywall, or rigid foam. Pay attention to air sealing, and consider including a better insulation product than fiberglass batts.

2. 
   davidmeiland | Dec 05, 2011 11:26am | #2

   First, no it is not proper for the batts to simply hang by friction between the joists. They should be supported by the drywall ceiling. The ceiling is the surface being insulated, so it should have the insulation against it. I don't have a clear picture of the construction there, but it sounds like you need to place the insulation against the drywall and do whatever else is necessary to make a continuous barrier with whatever insulation is adjacent in walls, other ceilings, etc.

   Second, shower/tub install areas are a big problem. What you are describing is that the drywall is not continuous and therefore cannot be the air barrier. If you can complete the sheathing on the attic side and make that the air barrier, it is probably the right approach. Of course there needs to be insulation installed too, and holes around pipes should be sealed.

   Last, that insulation that's hanging between the studs is useless. It needs an air barrier material (plywood, drywall, rigid foam insulation) installed, preferably on both sides if it's fiber insulation. It needs to be correctly stapled to the face of the studs (assuming it has facing).

   It can be hard to determine the best way to deal with these issues if you don't have experience. If you are inclined to find and hire a home performance contractor, you might get a lot of improvement for fairly small money. I know a lot of building contractors that don't know how to deal with this stuff, let alone homeowners.

3. 
   dontww | Dec 05, 2011 03:30pm | #3

   Martin and David,

   Thank you very much for your speedy and detailed responses. You've clarified the issues for me but I see a dilemma in trying to establish a continuous air barrier from the attic side. Without demo'ing the drywall and restarting, at best I can create a lap joint between the existing and proposed new drywall. With caulking, would this perform as an air barrier?

   I would like to reuse the fiberglass bats strickly for economic reasons. I don't see any way to staple the kraft paper to the studs however. Do you have a suggestion on how to do that from the attic side?

4. GBA Editor
   Martin Holladay | Dec 05, 2011 03:40pm | #4

   Don,
   Drywall, rigid foam, plywood, and caulk are all suitable air barrier materials. You don't have to use flexible sheeting as your air barrier. Here's more information on air barriers: Questions and Answers About Air Barriers.

   While you can't suspend fiberglass batts in midair without some method of holding them up, there's nothing wrong with friction-fit batts between studs, as long as the batts aren't slumping, and as long as the batts are touching an air barrier on both sides. Wall batts don't have to be stapled.

5. 
   dontww | Dec 05, 2011 04:07pm | #5

   THANKS!

6. 
   dontww | Dec 10, 2011 09:33am | #6

   I've finished adding drywall behind the tub to form an air seal and now realize a problem with the plumbing. Essentially, the plumbing is in an exterior wall. The problem is exacerbated by a design factor: the supply lines for the bathroom sink traverse the wall from the shower/tub but have to cross the vent stack. The plumber chose to locate the copper supply lines to the outer side of the wall cavity. That means that the supply lines are about 1/2 in. from the outer edge of the 2x4 framing. With the original construction having no air barrier on the outside, I think the plumbing was kept from freezing by the heated air that was escaping from the inside. If I now restuff the insulation and face the outside with OSB, will I create a freeze condition for the supply lines?

   I could add 1" of rigid foam to the outside but I fear that will create another problem: won't the insulation be trapped between two moisture barriers (the drywall and kraft paper face of the fiberglass bats on the inside and the foam on the outside)? I'm limited to no more that 1" by the clearance between the wall studs and the vertical supports of the roof trusses.

   Regards,

   Don

7. 
   davidmeiland | Dec 10, 2011 11:28am | #7

   If possible, you relocate the copper as close to the interior as possible. Either way you insulate it with pipe insulation. Whether or not it will freeze depends on your local climate. Plumbers in the area should know what and what not to do, and can advise you. Where are you located?

8. 
   dontww | Dec 10, 2011 04:06pm | #8

   David,

   Thanks for your response. I live in Michigan so freezing is a real possibility,

   Don

9. 
   dontww | Dec 31, 2011 11:50am | #9

   I'm part way finished and have run into another issue/challenge. If we think of the upstairs rooms as a large box with one side common to the exterior and the other three common to the attic, side one and two are now sheathed with OSB. The sheathing of the third attic side is complicated by a raised ceiling on the first floor. That means that the bottom sill for the third side is approx 24" below the ceiling joists. I could continue sheathing the outside of the framing if I add blocking above the joists, but there is no way I can sheath all the way to the bottom plate. Should I use this approach or replace the existing fiberglass bats with friction fit rigid foam?

   For wall two, the inside wall parallel to the outside face of the house, I'm severely restricted in what I can do by the design: vertical supports of the roof trusses are less than 1 in. away from the wall studs. OSB was the only sheathing choice. Wall three, however, is perpendicular to the outside face of the house and is not obstructed by the roof trusses, so I could use thicker sheathing. The only access to the attic is through a hatch, though, so I am restricted to materials 2ft x 8 ft. Does it make more sense to use rigid foam sheath on this third wall (i.e., adding the blocking and leaving the original bats in the walls)? Will this create a moisture problem with the paper faced bats on the inside?

   The first wall in the attic was sheathed with OSB by the contractor. Can I sheath over that with rigid foam or will I create a moisture problem between the paper faced bats on the inside and the OSB and rigid foam on the outside?

10. GBA Editor
    Martin Holladay | Jan 01, 2012 06:34am | #10

    D Mikulec,
    Q. "The first wall in the attic was sheathed with OSB by the contractor. Can I sheath over that with rigid foam or will I create a moisture problem between the paper faced bats on the inside and the OSB and rigid foam on the outside?"

    A. You can cover the OSB with rigid foam, as long as the rigid foam is thick enough. To determine the minimum R-value of the rigid foam in this location, I would follow the rules presented in this article: Calculating the Minimum Thickness of Rigid Foam Sheathing.

    Concerning your other questions: it's hard to visualize or describe solutions to the air-sealing dilemmas that you describe in your latest post. Air sealing work in an attic can be tricky. My advice is to follow the general principles of air sealing: if you know a crack or a hole exists, you have to find a way to seal it. Good air barrier materials include drywall, OSB, plywood, rigid foam, sheet metal, and spray foam. Remember to seal the perimeter of any sheet materials used as an air barrier.

    If you can't install any sheet materials in the areas you describe, it may be necessary to use spray polyurethane foam. You can get two-component spray foam kits from many lumber yards for $400 to $600.

11. 
    dontww | Jan 01, 2012 11:38am | #11

    Martin,

    Thanks for your response! I didn't expect it today, much less so early.

    Regards,

    Don