Building Science Projects

Safe Effective Affordable Retrofits

This project looked at retrofit options that could serve as an alternative for exterior foam board, using the Mobile Test Lab to evaluate several wall configurations for moisture performance.­ It found that vapor permeable exterior insulations offer an affordable alternative to foam retrofits.

1. Our latest study of wall retrofits suggested that using cellulose as exterior insulation instead of foam board allowed for better moisture control within the wall. Because cellulose is more permeable to water vapor than foam, it is less likely to trap moisture in the wall.

2. Another retrofit approach includes air sealing the wall sheathing by adding an air barrier without adding any exterior insulation. This wouldn’t improve the R-value of the wall but would be less expensive than a full exterior insulation retrofit (such as the REMOTE wall) and would still save energy by reducing air leakage.

Both approaches avoid trapping moisture in the wall assembly while aiming to reduce the cost and complexity of retrofits. This project established more background on these approaches, including a literature review, modeling, and interviews with contractors.


TitleTypeResource Link
Durable Envelopes ReportReports


Furring In an Outside WallVideos

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Safe Effective Affordable Retrofits ReportReports


Safe Effective Exterior Wall Retrofits SnapshotSnapshots


Safe, Effective & Affordable Retrofits for Cold ClimatesReports


Using Vapor-Open Exterior Insulations in Wall RetrofitsSnapshots


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