How to Insulate my Ceiling / roof deck
I have a pole building with metal siding, wood framing. The ceiling/roof currently has 2" vinyl backed fiberglass blanket insulation. I want to increase the insulation value of the roof without putting in an actual ceiling if possible. I don't think my trusses are engineered for a ceiling. and they are spaced way far apart. There is NO eve vents or any vents. If I need to vent I would lean more towards gable vents as I have no eve overhang to work with so would have to re roof all together. The goal here is to do this correctly with as little cost as possible and still keeping it simple.
The insulation blanket that is in place right now is in good condition.
I have talked with insulation companies and have gotten very conflicting information.
1. One place told me to just add in F-Glass rolls between purlins (no air gaps) then put another vapor barrier on the purlins and call it good. (My concern here is there is a double vapor barrier...maybe this is ok )
2. I was also told to slit the current blanket then add in the F-Glass insulation then put in a new vapor barrier. (my concern here is if moisture gets in the insulation the purlins will be in the we insulation ... maybe causing rot?)
3. I have also been told to just use spay foam directly on the current insulation blanket. (Not sure if the spay foam would damage the insulation blanket, and would be $$$ but might work with no ventilation)
I really do not want to put a flat ceiling in as it would be a very very short ceiling and I would loose a good amount of light as you can see where the bottom of the truss is in this photo. I am also not sure with all the construction and lumber I would need if it would save that much money over spray foam in the worst case scenario, More information would be needed on that. Spray foam for 2" would be ~1,200 and ~1,800 for 3"
If idea number 1 would work that would be cheapest and easiest....
I also have no had wiring done so I was thinking I would run conduit on the ceiling to avoid having wiring coming in and out of the vapor barrier so the VB would be as perfect as possible.......
This room will be used as a computer shop / workout room