Do I mount the roof access hatch on or in the roof opening?

The mounting flange of the roof access hatch should always be affixed to the surface of the roof.

The mounting flange has pre-drilled anchoring holes. Make sure the mounting surfaces are perfectly level on all four sides and fill any gaps. The mounting flange must be perfectly flush with the roof surface to which the roof access hatch is attached. Mount the roof access hatch so it cannot twist or bend.

Complete installation instructions in PDF format can be found here.