Is foamboard insulation on top of ceiling joists a bad idea? Is there a better solution if I can't have insulation directly on top of ceiling?

Question

I'm installing Armstrong Woodhaven ceiling panels in the kitchen of a ranch home, so the panels will be attached to the ceiling joists, with the backside facing up into the attic (the ceiling is currently open, and I believe the previous insulation was a couple of inches of rockwool).

Armstrong specifically says not to lay insulation directly on the ceiling panels (I believe it's a matter of supporting the weight). I happen to have enough 1" Foamboard insulation laying around to cover the kitchen, so I'm thinking about laying the foamboard on top of the ceiling joists, foil-side up, to make up for the lost insulation. The joists are 2x6s, and the ceiling boards attach to a mounting track, leaving about 5.75" of open space between the ceiling and the foamboard.

Questions:

1. Is this a bad idea for any reason?
2. Could I add blown-in or batt insulation on top of the foamboard?
3. Given the ceiling requirements, is there a better solution?

This is a 1950s brick ranch in southern Ohio with an asphalt shingle roof.

Answer 1

Question 2 - you can add insulation on top, but you're going to have a heck of a time not going though the ceiling. The foamboard won't hold you up if you step on it between joists, and it conceals where the joists are.

Question 3: - Yes, but it's more work. Nail battens (narrow strips of board) along sides of the joists at the bottom of the joists, to support foamboard cut to fit between the joists. The foamboard rests on the battens, not the ceiling material; then add more insulation on top. When needed, you can locate the joists in the loose insulation so you you don't go through the ceiling, and you have more depth of insulation. So a better job for the more work.

If you have space for it, an alternative is to run battens across the bottoms of the joists, and attach the ceiling to the battens, but that lowers your ceiling by the height of the battens and might be more of a change in the ceiling than you want. Battens support both ceiling and foamboard and keep the two apart. It's also a standard way to deal with the joists being out of level, because you can shim the battens level. Not that you mention having that problem to solve

Answer 2

If you can, I'd simply install sheet rock to the joists and then install the panels using the furring strip method.

These panels are not designed to provide an air barrier. In addition, they require some movement to keep from buckling. These combined means you effectively have a sheathing over your ceiling, not a ceiling replacement.

The simplicity of drywall means you can tape it to make the room air tight, and the strength of the drywall means it can both accept the furring strips below as well as the weight of (a reasonable amount) of standard insulation above.

As for using foam board insulation between the joists, I would recommend against it; as, the ends of the foam board won't hold weight well between the joists. While you might pressure fit them satisfactorily at first, as the home settles, you can expect these boards to drop out, onto your ceiling panels, ruining the effect as these panels are not designed to take load.