Another insulation question

[leog]

So I am considering using 3" polyiso foil backed sheets for insulation in my building. Walls are 2x6 frame. Would the smart thing to do be install flush with the stud and cover with drywall leaving a dead air space between outer wall and face of insulation or **** the up against the osb that is the outer wall? Also considering install in rafters, rafters are also 2x6, I believe that leaving the dead air space between the rafter face and the roof decking is the proper way to install for this part of the project. Seeking input from all.

Thanks in advance for all
Leog

 

[mrramsey]

Airspace between the roof deck and insulation IF you don't have a ceiling. If you have a ceiling I would blow in cellulose. For the walls put the panels tight to the OSB and fill any gaps with expanding foam (great Stuff)

 

[Black Oak]

you have a 5 1/2" wall cavity, as did I. I went with 1.5" foam, tight to the exterior, which allowed a small 1/2"gap for a airspace or "thermal break" , and finished with reg. 3 1/2" batts. Foam panels can be a budget breaker for many people. My compromise has very good in my shop. Foam in a can for foam panels if you can swing it, huge change.

 

[Black Oak]

Put your location in and that helps those that want to give advice.

 

[leog]

location is NE Ohio about 15 Degrees at present

Thanks for asking will remember in the future