I assumed it was to allow for expansion/contraction due to temperature
changes, which is why I was concerned about glueing down a new roof.

I suppose I could do a test: mark a few points and measure between
them at different temps.

Now another question...Can/should I use exterior plywood for the
underlayment instead of the [current] Iso-Board?

On Apr 23, 6:45*pm, Big_Jake wrote:
You have a real oddball there, Mike. *Typically flat roofs are done in
bitumen (torch-down), EPDM (rubber), or tar & gravel. *Rubber roofs
typically have a service life of around 40 years, glued down, in all
sorts of weather. *Temperatures should not be an issue, but uplift can
be, depending on the size of the roof.

JK