Originally Posted by SRG
If the rafter bays are regular and neat, why not just cut the foam panels to fit between the rafters tight to the sheathing? They will stay put w/ pressed in fit or with small cleats, you can add another layer now or in the future, they can be removed easily if required, it looks better/more interesting, and you will save some space/headroom.
My garage is done this way and it works fine.
I don't have a problem with headroom. There is no sheathing, look at my pics on the first page. It's a lot easier to grab a 4x8 piece and stick it to the ceiling than cutting it to fit a zillion different cubby holes. And then I will have the dead air space between the insulation board and the metal roof to add to the r value.