Slab edge insulation and expansion joint all in one? – GreenBuildingAdvisor

Greetings all,

In my upcoming garage/workshop build in 20878 (Md.) I’m planning on using 2″ of Comfortboard 110 or Foamular 250 under slab, vertically inside my stem wall, and vertically between my slab edge and stem wall.  In the latter location, the insulation will serve as both insulation and expansion joint, which if I understand it correctly is a typical strategy.  My architect has said that either of my insulation choices will not work in the dual insulation/expansion joint situation and wants to add an industry standard expansion joint strip to the slab edge side of the insulation.  He said that the insulation will crush, and not bounce back, leaving a gap.  I’m so used to seeing designs on this site without a separate expansion joint that I didn’t think that this would be a problem.  Can anyone provide me with a proper explanation of why my preference (i.e. Comfortboard 110 or Foamular 250, without additional expansion joint material) is OK, in an Architect’s or Structural Engineer’s language that my Architect would understand and accept, or am I incorrect in my assumptions?

Thank you,

Dave in Md.