A friend (not me, really!) went around their builder and insulated (fiberglass bats in stud cavities and roof joists) their 3-season porch before the sheetrock was installed. They also paid the heating sub to run ducts (supply only) into the room. The room is closed off from the house except for evenings and weekends. Predictably, they have a terrible condensation problem now that winter has arrived but here's the question: The builder built the porch (uninsulated floor) over a crawl-space that is open to the basement. Isn't that a big problem even without the forced-air and insulation?