[AC_Hacker]

I live in Western Oregon where the Heating Degree Days are about 4500.

I started my energy retrofit years ago. I used to think that putting fiberglass in the wall was enough, but I have since learned that just putting fiberglass in the wall is just a little better than nothing.

Since then, my approach has been to remove the inside finish layer, fir out the wall thickness to 6 inches, and fill the walls with rigid foam, caulking an foaming at all edges and seams, and staggering layers, and caulking an foaming, etc. It's a tremendous amount of work, but the results are encouraging. I'm considering external insulation too. I did not know about thermal bridging until relatively recently. Exterior insulation should remedy this.

I have a friend in this area, who has wrapped his house with 3 inches of EPS foam and he is reporting very good results. However, he is also reporting post-retrofit need to control drafts, so the advice given above concerning air leaks before retrofits is very important.

Also, as randen has said, considerations affecting dew-point are very important, and are affected by local humidity & temperature & insulation thickness. You do not want the dew-point to occur inside your wall or at a wood layer.

I see that BuildingScience.com has free information concerning all of these issues.

And lastly, when you have achieved the level of air-tightness and insulation that you seek, you'll need a mechanical HRV or ERV to assure a healthy indoor environment, so it's good to consider where it will go before you start your work.

-AC_Hacker