The toughest details are those that have to match up with someone else's work, or those done — even done well — when energy was really cheap. These details are a collection of some common — and tough — dovetails of existing work with retrofits or additions. Bear in mind that green remodeling means creating a new operating regime that is better, not worse, than the one that may well have been working just fine before. Integration of energy efficiency, moisture management, and indoor air quality is much more important and challenging in remodeling than in new construction.
Just as with new walls, Green Building Advisor employs rigid exterior insulation for retrofitting. It gives great bang for the buck thermally (insulation and air sealing), warms the existing framed wall reducing the potential for condensation in the cavities, and makes continuous air and thermal barriers much easier than working from the inside.