Exterior Insulation Done Well: Best Systems for Deep Energy Retrofits

In this episode of 7 Minutes of BS, we continue the discussion with engineer Jonathan Smegal of RDH Building Science Laboratories to break down the best exterior insulation retrofit systems based on real-world testing on five identical student housing units.

Jonathan walks through what separates a good system from a great one — fewer layers, less thermal bridging, lightweight claddings, and a dedicated air and water barrier at the sheathing layer. His preferred approach: remove the cladding, add sheathing if needed, apply an air- and water-barrier, then install exterior insulation with strapping on top.

Dan also makes the case for EIFS (Exterior Insulation Finishing Systems), which can be applied directly over existing brick — keeping thermal mass within the envelope, reducing landfill waste, and nearly eliminating thermal bridging when the foam is applied adhesively.

Key takeaways:

• All five tested systems performed well for energy efficiency and durability
• Fewer installation passes = lower cost and less complexity
• Air and water control belong at the sheathing layer, not split across multiple materials
• EIFS offers exceptional design flexibility and near-zero thermal bridging