Q&A: A Forum for Green Building Experts and Beginners

I had an energy audit yesterday, and they claimed I could get a 5 year payback by adding more attic insulation. I found a payback calculation online, and that came back with 30 years. I want to do the right thing, but it also needs to make financial sense. Anyone have experience with the payback calculation? I put my specifics in the "more explanation" section. Did I do it correctly? Hoping to find someone smarter than me (that part won't be hard) to help. Thanks.
--------------------------------------------------------------------------
Current insulation is R30 – fiberglass

Hi I have a cape in NY with knee walls on second story that were batted 50 years ago. The knee wall studs are only 2.5" wide (not usual 3.5"). The insulation is pretty beat in places. The floor of the knee wall is insulated over the ceilings below. There is a new roof cap in place that allows air to move up the rafter area. My question is what is the best way to insulate or re insulate the knee walls?

I was thinking of just adding a 2" rigid foam over the existing knee wall studs. Probably should replace the batting also though? I really dont want to replace the entire knee wall studding.

My contractors and I will be partially rebuilding a 40' section of 8' tall west-facing wall. We/I plan to use external rigid foam and vertical vinyl siding. I realize there are some risks with these types of walls, so I'd appreciate if the community would look over the planned design and point our risks.

The climate is zone 5a (or almost 6a), about 30 miles north of NYC.
The construction from inside to outside is planned to be:

- Lowes Valspar Signature "paint+primer" (unknown permeability rating) or sealed bathroom tile

I am building a house with closed cell foam sprayed in the rafters under the roof deck. This will put a vapor block at the soffit.
I am building a house with closed cell foam sprayed in the rafters under the roof deck. This will put a vapor block at the overhanging roof.
The roof overhang is two feet. Do you think the overhanging eaves should be vented? (The house is in Rhode Island (climate Zone 5-6)
Thanking you in advance,
Paul Sardelli