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Community and Q&A

Room above a garage

Scott Goodman | Posted in GBA Pro Help on

I have a room above a garage that I am turning into a bedroom 12/12 roof pitch Cape. The plan is mineral wool cavity insulation R-23 walls, Pro Clima Intello , 2 1/2″ service cavity with r-10 rigid mineral wool. Roof will be insulated from floor to ceiling with r-30 mineral wool cavity,Pro Clima Intello 2 1/2 cavity with r-10 rigid mineral.The roof will have a continuous 2″ ventilation made out of 1/4 osb as vent material and air sealed Bedroom floor / Garage ceiling will be r-30 mineral wool batts, Pro Clima Intello, 2 1/2 service cavity with r-10 rigid mineral, Is this a good insulation plan. Do I have to worry about exterior sheeting of the roof and walls becoming to cold or dew point problems?

Thank You

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  1. GBA Editor
    Martin Holladay | | #1

    First of all, it would be helpful to know your location or climate zone.

    You are planning to insulate your walls to R-33. That's good.

    I understand that you will be insulating your sloped roof assembly, and that you want to make this a vented assembly. So far, so good. You will be insulating the sloped roof assembly with R-40 mineral wool. That will meet minimum code requirements in Climate Zones 1, 2, and 3, but it's not enough for Climate Zone 4 or anywhere colder.

    Your plan to insulate the floor assembly to R-40 will work.

  2. Scott Goodman | | #2

    My location is Western New York which is Zone 5. The flat ceiling area of the room will have an additional r -15 for a total of r-45 and I was wondering if i should install another layer of Intello or Mento on top for air tightness. What should the sloped area be insulated to?


  3. GBA Editor
    Martin Holladay | | #3

    If I understand you correctly, your room above the garage will have two types of ceiling: some of the ceiling will be horizontal, and some of the ceiling will be sloped.

    If building codes aren't enforced in your area, you could choose any insulation level you want. If local codes apply, you should contact your local building department to find out what is required in your area.

    Since this is a green building site, we urge builders to meet, at a minimum, the requirements of the 2012 IRC. In your climate zone, that means that your ceilings (both the flat sections of the ceiling and the sloped sections of the ceiling) should be insulated to at least R-49.

    For more information on different ways to insulate a sloped ceiling, see How to Build an Insulated Cathedral Ceiling.

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