What’s the Best Path to a Deep Energy Retrofit? – GreenBuildingAdvisor

By Chuck Bickford | November 3, 2025

The term deep energy retrofit (DER) can make even the most seasoned homeowners or contractors nervous. It’s an ambitious goal—to make a home dramatically more energy efficient—but one that can be daunting in scope and cost, especially when the original builders made no provisions for efficiency upgrades. (For a detailed case study, see Jon Harrod’s experience with a deep energy retrofit.)

Recently, GBA member “littlegojira” (we’ll call them Gojira) shared their ongoing retrofit project in northern New Jersey (Climate Zone 5A). Their 1938 center-hall Colonial has two bay windows, brick siding on the first floor, and shingles on the second. With the siding stripped away, Gojira plans to add 3-in. of rigid mineral wool (Comfortboard 80) over a Benjamin Obdyke SA textured WRB, followed by a ¾-in. pine rainscreen.

The tricky part? The second floor extends 2½-in. beyond the first, creating an overhang that complicates how to bring both walls into the same plane once new insulation is added.

Two Options for Leveling the Wall

Gojira sees two possible solutions:

1. Add extra insulation – Install 3-in. of mineral wool, then add 2½-in. more on the first floor, followed by a ¾-in. rainscreen.
2. Add framing – Install 3-in. of mineral wool, then screw 2x4s laid flat to the first floor and nail 5/4 pine rainscreen boards to the framing.

Gojira said they assumed they couldn’t fur out the wall first, “because that would create an air gap and defeat the purpose of putting the insulation on the exterior.” Removing the existing sheathing and packing out the studs, they added, was “most likely cost-prohibitive but remains a possibility.”

So, what’s the best approach?

Member and expert insights

Option 1: Level the Overhang with a Bracket System

User “Rudy21” suggested using the InSoFast X-Bracket System, which can help level the overhang…