This three story, two family in Somerville, MA, underwent a remarkable transformation with an 'exterior' retrofit which included insulation as well as an additional layer of windows.

Mike Duclos of the DEAP  Energy Group performed the computer modeling and consulting on the various sub-systems, including space heating, domestic hot water, ventilation and renewable energy.
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A portfolio of our Deep Energy Retrofit work, complete with 'all the numbers' is available here.

An outstanding Green Building Advisor article  by Cador Price-Jones, an early 'pioneer' of DERs in Massachusetts who has 'walked the walk.'.