Replies

1. GBA Editor
   Martin Holladay|Oct 14, 2015 03:44pm|#1

   Scott,
   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|Oct 14, 2015 06:52pm|#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?

   Thanks
   Scott

3. GBA Editor
   Martin Holladay|Oct 15, 2015 06:08am|#3

   Scott,
   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, seeHow to Build an Insulated Cathedral Ceiling.