Extract current insulation before spray foam in the attic?
I am going to spray foam my attic, underside of roof, and all penetrations with open cell foam to air seal that portion of my conventially built and insulated house. My contractor is telling me I must extract the current fiberglass loose insulation now on the attic floor. While I am willing I can’t fully understand the science of needing to extract the current insulation. I am being told there would be two thermal barriers and with AC ducts in the attic the would be a moisture problem.
Anyone have advice or help with the science of this decision.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part