What makes the Northwest unique? Green trees, pristine beaches, and live volcanoes? Yes, but what makes building homes in the Northwest unique? Give up? It's the size of stud used. Throughout the rest of the country builders rely on the trusty 2x4. But here in the Northwest the energy code has demanded that the 2x6 become the weapon of choice. So what do we do with the 2x6? We space them 16" apart and fill the cavities with R-21 insulation. Every where else they do the same thing but max out with R-15 high density batts. Crazy! While Portland, OR uses R-21 for it's 4600 heating degree days, Minneapolis allows R-15 for it's whopping 8000+ heating degree days. Seems insane to me.
Now, let's say you want more insulation. You could use the 2x6 stud, but keep in mind your wall will still be 33% - 50% less insulated than your floors or ceiling. (That's okay, heat rises, right? Okay smart guy, if that's the case, why insulate your floor? 'Heat' does NOT rise). Digressing, you can see that your walls are seriously hampered compared to your hat and socks. How do you feel about 2x8 walls with R-25? Not well, I suppose. But what about 2x6 walls at R-21 with (wait for it) 2" of EPS rigid foam insulation? Suddenly you've come close to R-30 for your wall. Not bad, eh? And if you're still stuck on 2x4 studs with R-15, 3" of EPS rigid foam will bring you to a more comfortable R-27. Besides that, exterior foam makes a great thermal break between your studs and the outside world.
Since Istockhouseplans is a Northwest company, we've been used to the idea of specifying 2x6 studs on all of our plans. If you are a builder anywhere else, please don't let that stop you from using our plans. Simply use our blueprints and replace the studs with 2x4. Though our drawings show 6" thick walls, our details specify that either 2x4 or 2x6 are acceptable. If it's really a breaking point with your jurisdiction, let us know and we'd be happy to redraw the plans at no extra charge. That's our service to you.