Hi guys,

Lately I’ve been posting re: insulating some attic access doors with ridgid foam on my 1.5 story 1921bungalow in Minneapolis.  However, I’m still considering going with “hot roof” or unvented attic for several reasons.

1.  There are some short runs of HVAC duct up there.

2.  I think it would be very difficult to get good seals on all three attic access doors (there are three seperate attic areas around the finished space up there).

3.  Would allow me to use the area for storage (as opposed to adding insulation above floor boards)

4.  Current venting is a joke.  Each attic space has one vent at the eve end apx 8×8″, and one power vent blower.  I have disconected the fans, leaving only the vent housing because some of them didn’t work and I assume with only the one intake vent that they were pulling conditioned air out of the house.  Better venting would be a bit of a pain to retrofit.

So, out of curiousity I had a Icynene installer come out and take a look, and he quoted $840 to insulated the roof decks with 4″.  I have 2×4 rafters, and he says they would “bridge” over them with the foam to help keep the rafters themselves from conducting heat.  This includes going down to the rim joist as long as I take up the floor boards in that area and move away some of the celluose that is currently there so they have access.

EDIT:  Just had another Icynene installer estimate.  this guy recommended same as above, except adding some 2×2 to the roof rafters so he could spray thicker.  His quote was (including adding 2×2) $1000.  When I mentioned leaving the excess foam in place to cover the studs/rafters, he knocked $100 off (down to $900).  The other guy was not going to trim either.  Liked this one, showed up excactly as scheduled.  END EDIT

My concerns are:

1.  There is no acces to the roof area over the finished areas of the second floor, so that would not be sprayed.  However, a previous owner blew celluose up there.  Don’t really have a way to determine how much or how even the coverage is.  There is no venting up there, but I could add a gable vent and roof vent if I wanted.  These areas would be sealed from the unfinished attic space when the icynene was intalled.

2.   Roof replacement.  Current material is asphault shingles over what appears to be original sheathing (planks).  Unlikely to require replacement while I still own the home, but anything is possible.  I assume that the current sheathing could be left in place unless it really started to fall apart?

3.   Roof leeks- none that I know of, but… when I moved in there were some pans placed under one area of the roof near the eve.  I suspect that the previous homeowners (known to have done many stupid things) had some large ice dams that might have backed up enought to cause some leaking.  There is rubber ice shield under the shingles on the lower end of the roof, and I have been here two winters and never observed any leaking, even with some ice dams.

4.  Vapor barriers- there are none in the house that I know of, other than layers of paint.  Dry basement, panasonic bath fan on efi.org timer, range hood (crappy one though, need to replace).  Central AC installed.

General comments?  How about pros/cons of closed cell vs open cell (icynene or otherwise) in this application?

Thanks for reading my longwinded question!

Erik