Closed-cell attic spray foam, climate 4A, balloon frame 1924 house, dense pack cellulose already in walls. As I’m trying to prep the attic prior to the insulation, I am also trying to educate myself on some of the specifics so I will be able to get my preferences spelled out in the eventual contract. Often times details are left out and left up to the contractor. Part of the steepness of the learning curve is that if you’ve never studied wood-framing or observed your house’s framing up close it’s hard to visualize how things are actually laid out.

I had assumed that after the existing fiberglass insulation was removed, the foam would go all the way to the edge of the contained space–meaning past the top plate (two double 2x4s that define the edge of the house wall– and into, in my case, a fairly shallow overhang/soffit area ending in the fascia board. 4-5inches to my eye–we have a small overhang.

But from what I have learned on this site and others, blocking with various kinds of board is often applied–probably easier from the outside if it was open at the time–but that would also have to be covered from the inside with gypsum board or some other thermal barrier for fire protection. The two reasons this seems to be the case is a)the fascia board often has cracks in it from age or shrinkage, and if the foam is sprayed that far it will seep out the crack and possibly cause a huge mess that the contractor will have to clean up; b) the contractor doesn’t want to pay for the extra foam into the soffit area that is likely not necessary since it is outside the envelop of the building.

The contractors we have spoken to–all very experienced and professional–do not plan to use blocking. They will remove much of the exposed fiberglass–see attached photos–and probably intend to leave the balance past the top plate to act as blocking. It was pointed out to me by an experienced GC that that insulation should never have been stuffed into the edges like that and could have resulted in rot due to moisture buildup if the house hadn’t been so open otherwise. To my eye the pile of removed fiberglass shows no signs of rot, just the signs of decades of cold and heat. The black you may see is shreds of the backing paper.

Note the grey arrow in the diagram pointing to the same area as my photo shows.

So my questions are:
1-Is using the old insulation as blocking ok? Or should it be removed to prevent moisture buildup etc. and then the residual dust be vacuumed out to allow greater adhesion by the spray foam?
2-Should the spray foam only go a few inches past the outer edges of the top plate?