Windows can easily coexist with exterior continuous insulation of many thicknesses. With a whole building analysis, increasing the level of continuous insulation can allow for larger windows while maintaining the same level of overall building thermal performance. Modern detailing methods improve moisture management around fenestration openings.

Tools & Education

Intended to supplement the window manufacturer's installation instructions, where installation over foam sheathing is not specifically addressed. Also suitable as an alternative method of installation based on commonly accepted field practice. Available as a sealed code compliance report. 

Best Practices

Covers the most common method of flanged window installation over foam sheathing where the flanges are mounted directly over up to 2" of foam sheathing. Foam sheathing is used as the water resistive barrier. 

Covers a “window buck” concept with window flanges mounted directly over foam sheathing. Most common for wall with more than 1-1/2 to 2-inches of foam sheathing. Foam sheathing is used as the water resistive barrier. 

Covers a “picture frame” concept with window flanges mounted to the picture frame. Commonly used with foam thicknesses of 3/4 inch to 1-1/2 inches to match common lumber dimensions. Foam sheathing is used as the water resistive barrier. 

Covers a “rainscreen” concept with window flanges and furring mounted directly over any thickness of FPIS. Foam sheathing is used as the water resistive barrier. 

Guidance for the use of thick foam (>1-1/2") in wood frame buildings 

This presentation addresses two practices with proven ability to improve water penetration resistance of fenestration product installation: Sill pans and flashing for rough opening drainage, and air-sealing of the interior side of the rough opening gap.

This guide from Building America addresses various means of applying foam sheathing on 2x4 wood framed walls in climate zones 3-5, including integration with other components (e.g., windows and cladding) for foam thicknesses up to 1-1/2”. It also addresses air barriers,  water vapor retarders, and use of foam sheathing as a WRB or in combination with a separate membrane WRB.

Practical Research

Summary of WRB water penetration testing requirements and recommendations for the fair treatment of WRB products based on one performance-based benchmark for water-penetration resistance of WRB assemblies.

Additional Information

DOE Building America report from 2005 on installing windows into walls with foam sheathing used as an integrated drainage plane

This blog article captures the successful historic practice of installing flanged windows directly over foam sheathing, but also recognizes the utility of enhanced details when large/heavy windows or thick foam is used.

The water control layer of the wall has to connect to the water control layer of the window.