Has anyone heard of spraying foam insulation from the outside of the house? We are removing old siding and sheathing and would like to insulate with spray foam but don't know if it can be done this way. The interior walls are in good shape and most are original plaster so we don't want to disturb them. I have e-mailed this question to a couple of spray foam installation companies but never heard back. Maybe they think I am crazy!?