Since 10-15% of an exterior wall is studs, top and bottom plates, etc., the standard 2x6 stud wall, nominally R19, is actually only about R14. If studs were available made of 2" extruded foam sandwiched between two smaller studs (on the inside and outside of the wall), the thermal bridges of the framing would be eliminated. Wiring and plumbing could easily be punched through the foam. Standard fiberglass batts would fit in just as they do now. If additional strength were necessary, plastic bridging could connect the two wooden parts of the stud. A foaming fire-stop coating could be applied to or mixed into the foam.
An alternative, which would provide more of a fire stop, would be to cut a stud into two L shapes, separate them sideways, and pump foam in between. The only exposed foam would be against the sheetrock indoors and sheathing outside. This leaves more of a thermal bridge than the first proposal, but could use less wood than a standard stud.
2x6s generally provide an overbuilt frame anyway, as 2x4s provide adequate support in most homes, even at 2' on center. Either type of stud could be fabricated with rough-cut lumber for good adhesion, then planed only as necessary or desirable.
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The studs would lose a lot of strength if you replaced part of them with foam. However, you might be able to find a strong, high density foam that is nearly as strong as the wood. It might even be possible to make a foam stud that eliminates the wood altogether. It would probably increase cost though.
I've read about methods to insulate walls for sound. One strategy is to use studs that are narrower than the wall. For example, 4" studs in a 6" thick wall. The top and bottom plates are the full width. The studs are placed alternately against the outside or the inside panel. Thus, none of the studs touch both. Insulation fills the space between each stud and the panel that it doesn't touch. This does require more studs though. Usually, they put them 1' apart, so each side gets one every 2'. It might be cheaper to use studs at 16" with your foam insert instead.
Niceguy1706, I see your reasoning, but I'm in agreement with Dwane--If you use three-inch studs on a six-inch wall and stagger them, you've solved the problem without somehow making weaker studs.
Also note, a six-inch wall with foamular 150 (really 5.5 inches) would be R-27.5, not 19 or 14.http://insulation.owenscorning.com/homeowners/insulation-products/foamular-150.aspx
I'm still under the impression most houses are using 4-inch outside walls because it becomes a tradeoff of cost. When you consider the amount of insulation you can foam into a 4-inch wall compared to the little 1-inch thick on your refrigerator, 4-inch isn't so bad. Also, the primary heat-losers are windows and doors anyway--the r-value of a window is usually something like 1.5, even if it is sealing properly. Also, I think fiberglass insulation (R-19 at 6.5 inches) is more common than foam and it usually suffers from installation difficulties--even one snagged area and you can open a corner to not having insulation.
In the 70's when people really cared about energy savings, people designed houses with fewer windows, shorter ceilings, thicker walls. Recently I worked in a building with the whole outside perimeter made of windows, with 14ft ceilings.People just aren't that concerned about energy usage today. They're more interested in posturing green, but they don't set the thermostat at 65 (18C) the way Jimmy Carter did and houses are huge in the USA.
hrench, the R14 vs. R19 that I mentioned on a 2x6 stud wall is due to lower R-values (about R-5) everywhere there's a stud, top plate, etc. This same effect would reduce the value Dwane's R27.5 wall as well, although the bigger concern is the cost of 5.5 inches of foam board. My stud idea was intended to make a product already being commonly used more efficient. My own house is two stories, 2x4 studs @2' o.c., with 2" of foam board on the inside. The 2x4s are more than adequate, and this isn't just my opinion---it's documented engineering.
Agreed, hnrench, this wouldn't work as well on 4" walls, but if that's all one's climate needs, one may be okay with the lowered insulation value anyway. I'm more concerned with cold areas, where building standards haven't kept pace with rising fuel costs and environmental concerns.