In an end-unit townhouse, cell foam is being used to insulate the three exterior walls. Would the gains from also using cell foam on the party wall be noticeable? Or would the cheaper alternative of using traditional fiberglass insulation be sufficient? The neighboring house's wall will also be insulated separately on their side, most likely using fiberglass, so the R-value gains from using cell foam would likely be negligible. Our primary concern is reducing noise.
On a party wall between two adjacent, standalone houses, where each side is insulated, but between which there is not necessarily an air gap, would using cell foam insulation on the party wall provide noticeable soundproofing over fiberglass?