GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Should attic space over attached garage be blocked off for proper attic air sealing and ventilation?

jimcava55 | Posted in Energy Efficiency and Durability on

Pacific Northwest Region-Washington
Attic space over living space has loose fill fiberglass/no vapor barrier and is vented (double bird-hole eave intake vents and continuous ridge vent exhaust). Garage is sheet-rocked but attic space over attached garage is not insulated. Attic access is in garage ceiling.
Moisture problem evident on underside of roof sheathing. More apparent over living space than garage.
Plan to seal gaps and add insulation but curious about separating garage attic space.

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. GBA Editor
    Martin Holladay | | #1

    You are seeing signs of moisture on the underside of your roof sheathing. I'm assuming that you are talking about black stains (mold) or perhaps frost in winter.

    The usual moisture source in these cases is interior air leaking through the ceiling. The moisture is piggy-backing on the exfiltrating air.

    To correct the problem, you need to seal leaks in the ceiling. This will require you to temporarily move your insulation to expose the leakage points. Once your air sealing work is done, the insulation can be replaced.

    Typical leakage points: along the top plates of partition walls -- there is usually a crack between the drywall installed on partition walls and the top plate; plumbing vent penetrations; electrical penetrations -- especially at can lights and other electrical boxes; duct penetrations; flue penetrations; at attic stairs and attic access hatches.

    It's possible (although less likely) that air leaks through your garage ceiling are contributing to the problem. It can't hurt to air seal your garage ceiling while you are at it. You might as well install weatherstripping at the garage access hatch.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |