jgb wrote:

If you install Dow Styrofoam or Dow Tuff R both must be covered by 5/8
type x drywall for two reasons.

Section §RR318.1.2 of the NY State Residential Code requires 1/2"
gypsum board over all foam. There's no mention of anything thicker or
that it must be Type X.

1) Both products have high flame
spread/smoke developed characteristics and must be covered by code. 2)
Your garage wall is probably a one hour fire rated wall and will lose
that rating if it doesn't have firecode drywall on both sides of the
wall.

Section §302.3.3 exception 2 of the Building Code of NY State requires
5/8" Firecode for the garage ceiling if there are habitable rooms over
the garage, if not, then 1/2" drywall is acceptable for the walls and
ceiling.

R