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I live in Illinois and am building a 60x40 house with a metal roof and vinyl siding. I have heard about p2000 but I am not convinced if it works. What is the best way to insulate the roof and outside walls. All opinions are appreciated.
 

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Been researching building envelopes for weeks now as part of one of my current projects. All information leads to a typical stick frame structure with single faced SIPs (Structural insulated panel) on the walls and vented insulated panels on the roof (Coolvent - www.hpanels.com).

Wall Composition from interior to exterior:

1/2" gypsum walls board
2X4 studs at 16" o.c. with un-faced insulation fill (do not use a vapor
barrier at interior the 4" SIP panel is the wall's vapor barrier).
4" SIP panel
tyvek weather barrier
vinyl siding


Roof Composition from interior to exterior:

tyvek air barrier attached to rafters
2x? rafters at 16" o.c. with un-faced insulation fill
1/2" plywood sheathing
6" ventilated insulation panel
roofing underlayment
metal roofing panels


This type of construction allows for the complete freedom of electrical and plumbing rough work without affecting the insulation and vapor barrier envelope. This holds true for any future work or wall penetrations. An air tight, thermal bridge minimized envelope that provide R-30+ insulation.
 

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I'd say you need to investigate some costs and structural pros and cons of various walls, first. Buildingscience.com is a good resource to start with. For my situation, SIPs are not even in the discussion. They may work well for you, though. Make sure that whoever installs SIPs is familiar w/ air sealing them. A lot depends on who is building the place, too; you or hired folks. To me, it is hard to beat stick framing and dense packed cellulose; single stud or double stud walls. If you are thinking about minimizing global warming, SIPs don't quite fit in the picture. Whatever you do, leave the fiberglass batts at the store.
 
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