Another shed insulation question

[cousin eddie]

12 x 20 mini barn shed. Should I put radiant barrier on underneath the roof sheathing, or on bottom or rafters, leaving space between it and sheating? Should I use fiberglass insulation also? If so, between roof sheating and radiant barrier or between radiant barrier and workspace? Will have a uninsulated ceiling with a 4' x 4' opening to get to the loft. Will later on insulate walls, but for now trying to make it easier on my 10k btu AC. I appreciate any advice. It seems I am "search deficient", but I did try.

 

[PoorUB]

I would not recommend insulating against the underside of the roof surface. You should have air space there to help cool the roof. You could insulate under the rater itself and leave a 4" air space which I would ventilate with a ridge and soffit vent.
I have seen guys use 2" foam board insulation and nail it to under side of the rafters, then cover that with sheet rock, but you only get an R-13.

 

[nadogail]

Are you heating or cooling?

 

[cousin eddie]

Heat and cool, but mainly cooling. Figure I can always dress warmer, can only take so much off. I have a 10,000btu window type AC unit, which is about double what I should need from what I've read. Also, no windows.