Replies

1. Expert Member
   Dana Dorsett | May 24, 2013 03:52pm | #1

   Dense-packing cellulose or fiberglass into empty wall cavities will indeed retard air flow into the attic. For fiberglass this means 1.8lbs per cubic foot minimum, for cellulose it means 3.2 lbs min, but you may need/want to go somewhat higher in density depending on your climate. There may also be issues/problems dense-packing to the roof deck even on the part that's basically a wall, since the roofing material is too vapor-tight. This is again climate & density dependent.

   What is your location?

2. GBA Editor
   Martin Holladay | May 24, 2013 04:14pm | #2

   Sarah,
   If the underside of your roof sheathing is covered with mold, that's a strong indication that you have air leaks through your ceiling into the attic -- and is a clue that your house probably has a damp basement or crawl space.

   The solution is not more insulation or more ventilation. You need to identify the air leakage pathways and seal them. Only then should you consider increasing insulation or ventilation.

3. 
   sarahmatheson | May 24, 2013 04:16pm | #3

   My location is Castlegar BC, 3hrs north of Spokane WA.The Insulation Contractor wants to drill holes into the walls and fill with loose fiberglass.I do believe there is a single batt of insulation in the wall cavities so will this interfere with the even distribution of the spray in insulation?

4. 
   sarahmatheson | May 24, 2013 04:26pm | #4

   Martin, I think the the air leakage is coming from the exterior walls where you see the window in the side of the house.That room is a bathroom and someone privious to us did a bathroom remodel where they stuffed some insulation behind the drop tub and draped poly vapor barrier over top with out attaching it or sealing it. the bottom of what is the metal roofing is adjacent to the floor when I removed the exterior walls in the bedroom I could see daylight,so I sealed it. You are corecct about moisture in my basement I have cinderblock with efflorersence stains.

5. Expert Member
   Dana Dorsett | May 28, 2013 11:19am | #5

   In a southeastern B.C. climate insulating against the roof deck with cellulose or fiberglass carries some risks, since the winters are cool enough long enough to accumulate mold/rot levels of moisture. If you're planning to re-roof in the next few years and PROMISE to put rigid insulation on the exterior sufficient to keep the roof deck warm enough to not accumulate excessive wintertime moisture you can get away with insulating the cavities now. To meet code you'd have to put about R25 on the exterior (4" of polyiso, 6" if EPS or rock wool.)

   http://publicecodes.cyberregs.com/icod/irc/2009/icod_irc_2009_8_par093.htm (< your climate is comparable to US zone 6)

   But whether you insulate now or later, what Martin said- air-sealing is the first and most critical step.