insulation plans new construction ..HELP

[bdymnjm]

This topic is more complicated than I imagined. My detached garage is going to be 2x6 construction. It will have vaulted ceilings. I live in CT climate zone 5. In process of framing. I thought 1'' of foam would be a good start to insulate , plywood siding on top of that. In the future I can add more insulation. When all complete I want to keep the garage heated to 45 all winter and heat it up more when I am working. Probably 3-4 days a week. May need to cool it down on some days. No heat source yet. The build is on a budget so I will do what I need to get the basic building up and continue as I can. Will be used mostly for projects not daily driver parking so not much snow and rain water off the cars.

The future insulation is what I am not sure of. I wanted to add fiberglass with the facing or a vapor barrier under the interior osb or drywall. I wonder if this will create trapped moisture in the wall because the exterior foam will also be a vapor barrier and also 1'' of foam may not be enough.

The foam HD sold me is r6.5 foil backed 2 sides. I didnt expect that but maybe it will be good to reflect the heat this summer. I think I will put strips of wood under the siding to leave a gap to allow airflow up behind it.

Any advice will be appreciated.

Jim

 

[James-W]

You are kind of in a bad way because you can't really put any kind of wall covering on the inside until you insulate. I suppose technically you can, but if you do you will have to remove it in order to put the insulation in the walls. Maybe you could drill holes in the walls and blow in some insulation, and some people do that, but I would think with 2X6 walls fiberglass R19 would be your best bet.

 

[stingry]

Why the foam? Just sheet the outside, put up R19 kraft-faced batts and be done with it. Why reinvent the wheel?


Cheers
Steve

 

[rsa]

•Install R7.5+ exterior rigid foam or mineral wool while you have the opportunity. Add interior insulation when funds are available.

http://www.greenbuildingadvisor.com/blogs/dept/musings/how-install-rigid-foam-sheathing
http://www.greenbuildingadvisor.com/video-how-install-rigid-foam-insulation-outside-house
http://www.greenbuildingadvisor.com/video-superinsulating-home-rigid-foam
http://www.greenbuildingadvisor.com...-wool-insulation-over-exterior-wall-sheathing
http://www.greenbuildingadvisor.com...lating-minimum-thickness-rigid-foam-sheathing

•Use a rain shield before you put on the cladding.

http://www.greenbuildingadvisor.com/blogs/dept/musings/all-about-rainscreens

•If you haven't ordered the trusses, assuming you are using trusses, get ones with a raised heel so you have enough room for insulation and venting over the top plate. How much? Put more insulation on top of the wall than inside it.

http://www.greenbuildingadvisor.com/blogs/dept/building-science/lstiburek-s-rules-venting-roofs
http://www.buildingscience.com/documents/published-articles/pa-crash-course-in-roof-venting/view

•In the last link, note that you can also use rigid insulation on the exterior of the roof deck (and omit the venting). Good if you have a complex roof or want the entire interior conditioned.

 

[theoldwizard1]

Why the foam? Just sheet the outside, put up R19 kraft-faced batts and be done with it. Why reinvent the wheel?

Got to agree !

You can use exterior rated foam board for sheating instead of OSB/plywood but you need to add additional bracing in the walls (called wind bracing).