[Hendo]

What is the best way to insulate a metal roof and the exterior walls of a new home.

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[AGWhitehouse]

I'm sure you'll get a lot of opinions on this. There is more than one way to correctly do it.

That being said, I've 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
roofing system (asphalt, metal, etc.)


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.

 

[Hendo]

There is no way I can afford to use 4 or 6 inch vented insulation panels they are $150 a sheet

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[AGWhitehouse]

If you're on a budget then the best way is the traditional way. Fill the cavities with fiberglass batt (some hate it) or cellulose. Fill your ceiling joists with the same and cover with an air barrier (tyvek) to mitigate air movement within the insulation. Be sure to air tight the system to ensure the insulation works at its full capacity. And remember that air tight does not mean vapor tight.