[rpf]

Seal the attic from the conditioned space, get plenty of attic ventilation, and DON'T insulate directly under the roof deck!!!

You think it's problematic with an air gap (I think 2" is recommended from what I remember) between the roof decking and insulation? Have you seen roofs where it became an issue?

It would certainly be preferable not to do it just for ease of checking roof leaks, but A/C equipment really should be in a conditioned space.

[Peter J]

You think it's problematic with an air gap (I think 2" is recommended from what I remember) between the roof decking and insulation? Have you seen roofs where it became an issue?

It would certainly be preferable not to do it just for ease of checking roof leaks, but A/C equipment really should be in a conditioned space.

2" gap should work fine provided that gap is vented continuously from eve to ridge in every rafter bay. Easier on a simple gabled roof, but things get more complicated with hips and intersecting roof lines.

[thunderbrick]

With an air gap, no problem.  I'm talking about spraying the underside of the roof decking.  Bad idea.  If the living space is not sealed from the attic you'll get energy losses, and proper attic venting will keep moisture down.