Wall / Roof Cross Section

[jhambley]

Need help determining what I need to use on the exterior and roof construction of my cabin. I would like to use a metal exterior/roof.

Is this the correct way to build?  (Working from the inside outward)

Wall
-------------
Finished Wall (Drywall, paneling, etc)
Insulation in Stud Wall
OSB Exterior
Tar Paper
Rigid Foam
Wood Furring Strips
Metal Sheet Panels

Roof
-------------------------------
OSB Exterior
Tar Paper
Rigid Foam
Wood Furring Strips
Metal Sheet Panels

Also, if I wanted to add a radiant barrier, where would it be placed? Do I need a vapor on the inside of the wall under the drywall?

Thanks for your help figuring this all out.

[MountainDon]

1.  Insulation and vapor barrier requirements varies with climate zone. What works in ND, WI will be a disaster in LA, MS. A vapor barrier on the inside in the hot and humid south, coupled with air conditioning is a mold factory.

2.  The use of rigid foam on the exterior with fiberglass in the wall and roof framing cavities can produce problems in some climates if the foam is too thin. If the foam is thick enough for the climate, the inside face of the foam will stay warm enough to prevent cold weather condensation against the inner foam face. Rigid foam in staggered layers, seams offset can make great vapor barriers in themselves. The seams and corners need caulking and/or tape sealing.

3.  Building Science is a treasure trove of climate related information for building. Browsing through their site is time well spent. Their on site toipic search works pretty well.

4. The position of a radiant energy barrier is dependent on where the radiant energy is coming from. Here in the SW the major issue is sun energy heating the interior in the summer. So my retrofit has a foil faced polyiso sheet as the last layer on the exterior. Then vertical furring strips screwed to the studs. A radiant barrier needs the air space to work. Three quarters of an inch is deemed good. That doesn't do much to help with heat energy escaping from the interior in the winter, but that is less concern. Plus the foam and fiberglass insulation do a good job at reducing the heat flow by conduction, which is more important, IMO, than any worry about radiant escape. FWIW, my two inches of exterior foam is about double the thickness required for my climate zone (to prevent condensation between the foam and the fiberglass). In ND, WI the foam would need to be thicker.

5. When using metal wall and roofing you use horizontal furring to attach the metal. That does make a problem with what to do about getting rid of any moisture that might find its way into the airspace. That can be countered by first attaching vertical strips, then the horizontal over the vertical. Tie all the furring into the framing.

[jhambley]

Thanks for the reply. I guess it's more complicated than I thought.

I live in east central Kansas about 1.5 hours south of Kansas City. I want to use blown cellulose instead of fiberglass.