Expert: Dan Griffin - 3/5/2011

Question
I have a metal storage shed about 400 sf, all metal construction.  The roof is metal battens, structure is about 1" angle trusses @2'.  Walls are metal panels.  There's no insulation, and I want to add some to make my shop more comfortable (in Minnesota)  The simplest mode to me seems to be to glue 1 1/2" foam board insulation to the smooth interior face of wall and roof deck, and glue 5/8 flake board sheathing over that.  Oh, walls are 8' high.

I'd appreciate comments and  other recommendations.

Answer
Walt, the rigid foam with OSB (probably 7/16) would help a bunch.  It would be good to create a physical connection for the sheathing rather than glue only.  Most adhesives loose their hold with high heat, and many of the rigid foams have a thin plastic film on at least one side, that is prone to separation. I don't know what dimension foam you are considering.  Let's work with 2" to see my idea.  Custom cut and install 2x2 horizontal at the floor, ceiling, and mid point.  The 2x2 can be glued and you can install screws from the outside of the tin sheathing to hold the wood.  Make sure to use rubber washered metal building type screws with plenty of threads into the wood.  Infill with the rigid foam and nail or screw the OSB to the wood sleepers.  Without seeing your roof trusses I can't suggest a way to install nailers, but again, I would be concerned about a glue only install.  If this is subject to inspection, the AHJ may well require a non flammable finish - gyp board.  I would not be uncomfortable with the OSB only, but you know how inspectors can be.

Check any adhesive you select for the foam to make sure it is compatible.  Most solvent based cosntruction adhesives will eat the foam.  There are some latex based adhesives that are commpatible.

The method we are looking at will force any and all electical work on the surface of the OSB.  An alternate would be to build stud walls with recessed electrical.

Just some food for thought.  YOu will want to paint the walls white as the OSB will be dark and dingy looking.  I hope some of these ideas help.