Why is exterior insulation considered when building retrofit for existing buildings?

• A. It reduces interior usable space.
• B. It reduces thermal bridging and improves envelope performance without reducing interior usable space; can be installed on exterior walls and accommodates existing interior finishes.
• C. It is only useful for new construction.
• D. It cannot be used on existing buildings.

Answer: (B)

Exterior insulation for retrofit adds insulation on the outside of existing walls, creating a continuous layer that reduces heat flow and minimizes thermal bridging through studs. This improves the overall envelope performance and energy efficiency without shrinking interior usable space, because the interior wall plane stays the same. It also accommodates existing interior finishes since the work is done on the exterior, allowing the interior layout and finishes to remain unchanged while the exterior cladding is updated. In practice, this approach is versatile for existing buildings and can be paired with new exterior finishes to improve durability and moisture management. Interior insulation would encroach on living space, and the idea that exterior insulation can’t be used on existing buildings or is only for new construction isn’t accurate, which is why exterior insulation is the preferred retrofit option.