I live in a duplex with a flat roof that has an attic that is under- insulated, about R 15-19, in an area where summer temperatures in the
90s are not all that uncommon. The attic, such that it is, is only about 24 inches tall total, with HVAC ducts present.To make the summers less unpleasant, I'm grappling with how best to cost-effectively add insulation. I'm inclined to do this myself, unless there is an overriding reason to get a contractor. Here are a few ideas:
1) add another layer of unfaced fiberglass batts. Nasty work given the space, but feasible. With the ducts there, only about 2/3 of the space is accessible. So it won't be very orderly. How problematic is it if the extra insulation is rather haphazardly added? Does this defeat the purpose?2) blow-in or foam insulation. Does anyone have some general guidelines of cost per sq ft to have a contractor do it? Is this at all a feasible DIY project?
3a) exterior insulation. There are 3 ft walls extending above the edges of the roof on three sides, so except from a back alley, the roof is entirely invisible. One option would be a couple layers of polystyrene (or comparable product) applied on top of the roof with tar as weatherproofing. This strikes me as less cost effective than options one or two, but there are no space constraints.3b) A second exterior option would be to build a plywood false roof (with tar weatherproofing) above the regular roof and place fiberglass insulation inside. I think this would cost less than 3a but would be time consuming.
What do you think? Any thing I've missed? Any feedback would be much appreciated.
Perry