Our construction company recently completed a major remodel and energy retrofit of a split-level home in northern Vermont. In addition to requesting a long list of interior improvements, the owners wanted to reduce their energy costs by adding more insulation and replacing their leaky single-pane windows. The key to keeping the project within the budget was adding the insulation from the outside in order to preserve as much of the interior finish as possible.

Working with architect David Pill, we considered a number of options for retrofitting the exterior insulation. On previous projects, we had wrapped walls with one or two layers of blueboard, then fastened the siding to furring strips installed over the foam. But with that method, it's tricky to properly flash window and door openings to the...

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