Polyiso vs XPS insulation for roof

[3rdgendslmech]

Looking to insulate the roof of my pole barn and install a radiant barrier. Temps got up to 84 this past saturday and there was a pretty noticable difference between being outside and walking into the barn. Dimensions are 24x32x10. Trusses are 2x4 and 4 foot O/C. Full length vented eaves and full length ridge vent.
Home Depot has R-Max 2" 4'x8' polyiso for $30.50 a sheet and according to R maxs specs its rated at R13. As of right now I dont have any set plans for heating, probably going to go along the lines of either a pellet stove or 2 5000W electric heaters to save floor space. No gas available in my area.

 

[bobbyjean]

i used xps for wall's ...it seemed tough enough to use on ceiling..not sure on 4' span though
......how about cat's or nailer's between trusses?

 

[theoldwizard1]

Poly-iso R rating changes with ambient temp, although most (all?) poly-iso has a foil barrier which helps in hot weather.

If you shop around, you can find reclaimed solid foam cheap. You will have to bring your own trailer to haul it.

 

[strutaeng]

Looking to insulate the roof of my pole barn and install a radiant barrier. Temps got up to 84 this past saturday and there was a pretty noticable difference between being outside and walking into the barn. Dimensions are 24x32x10. Trusses are 2x4 and 4 foot O/C. Full length vented eaves and full length ridge vent.
Home Depot has R-Max 2" 4'x8' polyiso for $30.50 a sheet and according to R maxs specs its rated at R13. As of right now I dont have any set plans for heating, probably going to go along the lines of either a pellet stove or 2 5000W electric heaters to save floor space. No gas available in my area.

You are installing under your roof, right? XPS has better vapor permeability than polyiso. Polyiso has slightly better R-value, but under really cold temperatures XPS performs better. Look up greenbuilder website.

I did an overbuild to part of my house and went with 1" XPS and 2 layers of 3" Polyiso. All joints staggered and the XPS also taped at the joints. This required additional decking and re-roofing that I already needed. It has worked well for me.

I will say go to a roofing supplier that sells commercial insulation. I believe I got 3" polyiso for like $35 per sheet.