Insulation, Radiant and Vapor Barriers - Cathedral Insulation question

Hello, I'm going to have my roof (4/12 pitch cathedral ceiling) in Vermont replaced soon and the latest proposal from a roofer is to remove everything from the existing 2X6 tongue and groove ceiling/decking and put down Typar RoofWrap 30 underlayment, then 4 inches of ISO foam board, then 1/2 inch OSB plywood directly over the insulation, then standing seam roofing over that (Kynar-500 coated galvalume, coil fabricated 24 guage, 1 inch high seam profile, double lock mechanical seam). No ventilation. I currently have 2 inches of rigid foil wrapped foam with asphalt shingles on top. My questions are these: 1. Is unvented OK since it's standing seam? 2. How much different will my energy bills be with the extra 2 inches of foam? Right now in the winter with heat source in lower floor, there's a 10 degree variation between up and downstairs. it get much warmer upstairs? How do I figure this out? I have been offered a less expensive option of just roofing over the existing insulation without adding more. Should I not bother to add insulation? Thanks CT

http://www.ornl.gov/sci/roofs+walls/insulation/ins_01.html

This site is an Insulation Fact Sheet by the US Dept. of Energy. It discusses your situation and the issues that apparently concern you.

http://www.veic.org/

This site is the Vermont Energy Investment Corporation (VEIC). This company is an Energy Service Conservation Organization (ESCO). However, unlike the ESCO's that have recently popped up in the past few years, VEIC has been around for decades. Because of this many of the Building Science Organizations and virtually all of the public power utilities on the eastern seaboard has VEIC as a consultant for advanced building methods and indoor air quality concerning energy conservation programs, both local and national.

Now I can easily give you my opinion concerning your situation, however, my view clearly opposes the opinions of nearly every Building Science Organization and VEIC's. Which means I am in the minority on this subject, Sick Building Syndrome (SBS). Since I did not give you my opinion, I will give you someone that can help you. KEN TOHINAKA at VEIC, you will find his Email address in the company's contacts. It has been 10 years since Ken and I worked together and I am not sure if he is still with VEIC. If you contact him or anyone in VEIC, just tell them you were referred to them by FRANK LAZARO from New Jersey, formerly with Honeywell DMC.

Why can't anybody answer this question? Will I get a lot of energy savings by doubling the roof insulation? Will standing seam handle ice dams with no problems? CT

I have spoken to more people about this roofing job, particularly the people at VEIC. I spoke to one of the consultants there and here was his suggestion:
Since the foil wrapped insulation is already there, and the foil effectively creates a vapor barrier, why remove it and start over? You should remove the old shingles, seal the rigid insulation with sprayable foam, then add another layer of the same, staggering the seams to avoid thermal bridging. Seal those joints too. Cover all with 1/2 inch plywood and put down the standing seam roof. No need for ventilation.
Would some of you please offer opinions on this idea? Thanks, CT

What is important here is that you have other opinions than just mine. Also these opinions should be supported. I firmly believe that regardless of the type of roof, it should be ventilated in areas where they experience more than 2,200 Degree Days, which your area does. One of the most compelling factors for my opinion is the 5 to 1 rule concerning vapor barriers. What this means is that any material that comes or is applied after the vapor barrier in which heat flows during cold weather, should have a 5 times greater “Perm Rating” than the vapor barrier. For example, if a vapor barrier is applied that has a Perm Rating of 1, then all materials applied on top of the barrier should have a Perm Rating of 5 or more. Since nearly all of today’s roofing materials violate this rule, there is the need for attic ventilation. What attic ventilation does is bypass the low moisture vapor permeability of the most common roofing material used today. Though many will argue the common sources for moisture problems in attics are a direct result of the by-pass phenomena and air leakage (air transported moisture) and not heat transported moisture (diffusion), we should not ignore the 5 to 1 rule, which is widely accepted. However, this is neither the time nor the place for this debate. As such the following is my recommendation;

1. Rip off the existing roofing to the tongue and groove planking.

2. Install an AIR/VAPOR BARRIER over the planking.

3. Build a frame on the planking using 2x4's or more.

4. Lay 2 inch rigid board insulation inside the framing, staggering the boards and foaming the ends together.

5. Once the inside of the frame is filled, cover with a 1/4th inch of plywood.

6. Install 1x2 inch slats from the bottom of the roof up to the ridge every 16 inches on center.

7. Install 3/4th inch plywood over the slats.

8. Then install any type of roofing material you wish over that.

The wood slats create an inch gap between the pieces of plywood from the bottom up to the ridge. There are a variety of ways to provide venting at the bottom by building soffit or eave vents and/or installing drip edge vents. Then use a ridge vent for the top.