Insulation help for my garage with pics

Spray foam works well if you understand the process. It becomes the vapor barrier, because it is closed cell, and bonds to the underside if the decking & supporting structure.

Properly applied, it will prevent ice dams, because the deck stays cold. Much easier to have a little gap develop in other types of insulation & cause a hot spot on a roof.

Two part spray in foam can be a DIY project. It is not anything like spray can foam, and requires some planning. It sets up in seconds once sprayed, and it is easy to spray deeper than you had planned.

It runs about 1 USD per board foot for DIY: http://tigerfoam.com/

That is E84 fire rated material, and is ok in lots of spaces. If your local building codes require it, there is a flameproof coating available to spray over the finished foam.

A 500 square foot garage is a reasonable DIY job. You need to do all of the work like penetrations, wiring etc first. I prefer to not put electrical under the foam unless it is in conduit for later service. Then you need to empty the garage, and mask the place from the underside of the rafters down. Plastic sheet, cardboard & a staple gun. Cover the floor. This stuff sticks to anything, and you are not putting it in with an airbrush...

Properly sealed up, the roof deck stays dry. Don't believe the rumors that it shortens roof life - plenty of homes here in the desert have the sprayed decks with great roof life at high temps. It is amazing to climb into an attic, and see bare sheetrock on the rafters - then you realize the attic is almost as comfortable as the rest of the house, and the HVAC equipment is running in a clean cool space. A 10 year old house with a foamed deck usually looks like they vacuum & dust the attic inside.

I would foam it in that climate. My home in Colorado was foamed, and it would have snow on the roof a week after a storm, while the neighbors roofs were clear. I could just see the heating dollars melting that snow.

B.