Well, at least for the 2nd floor ceiling.
Normally, you wouldn’t start the sheetrock till the walls are insulated. But in order to test how well (or poorly) we’ve sealed the house with a blower door test, we need to complete the air barrier, and that means the 2nd floor ceiling. This is the area where the air barrier transitions from the exterior of the house to the interior. It will be one of the trickiest areas to seal properly.
We installed gaskets around the top edges of the walls, but because we’re using strapping, it made it difficult to close all the gaps. So we’ve decided to use 2-part foam only around the edges where the ceiling meets the walls. This should ensure that we have all possible gaps sealed.
We used poly boxes at all exterior wall electrical box penetrations, but we totally forgot to do this at the 2nd floor ceiling. We’ll have to use a combination of tape and foam to seal light fixture electric boxes in the ceiling.
I think I’ve mentioned in an earlier post that a smarter way to air seal the top of the enclosure would have been to extend the exterior sheathing and air barrier over the ceiling joists. Then pile the roof insulation on top of the sheathing. This method has been used by Marc Rosenbaum, although the air barrier in this case was the roof.* This approach would necessitate raising the roof up a bit to ensure proper insulation levels at the eves. The extra expense of sheathing the top of the ceiling joists would have likely been offset by the extra labor and material costs spent sealing all the gaps with foam.