Foam plastic insulating sheathing (FPIS) products come in many thicknesses and R-values to accommodate almost any end use and can be used along with approved joint treatments (tapes, flashing, etc.) as an effective and durable water resistive barrier (WRB) to meet code requirements without the extra cost or labor associated with using a separate WRB product. FPIS products are offered in three types: Expanded Polystyrene (EPS) - ASTM C578, Extruded Polystyrene (XPS) - ASTM C578, and Polyisocyanurate (Polyiso) - ASTM C1289.

Tools & Education

Tools to help coordinate energy code thermal insulation compliance and building code water vapor control compliance for steel or wood frame wall assemblies on a commercial or residential building.


This session, presented at IBS 2017, provides actionable prescriptive guidelines for integrated insulation and vapor control strategies.


Follow these three rules to create an efficient, robust, and moisture-resistant wall assembly for optimal performance and code compliance using FPIS ci as continuous insulation, vapor control, air barrier, and water-resistive barrier.


Originally presented by Jay Crandell, P.E. at the 2022 IIBEC International Convention & Tradeshow, this presentation reviews structural wind resistance and water-resistance research supporting various detailing options in the context of new provisions in the latest editions of the IBC and IRC. 

Best Practices

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.

Four typical methods for window framing are covered here. The installation approaches shown all include windows with integral mounting flanges, and all use taped foam sheathing as the water resistive barrier.

This page illustrates the integration of code-compliance requirements and best practices for moisture control of frame wall assemblies (based on 2021 IRC).

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.

Additional Information

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

Four tests can help to sort out the dilemma of whether a water control layer can have holes and function as intended. 

One of the dirty little secrets that never gets talked about is that water leaks through building papers, building wraps and housewraps and runs down between them and the sheathings that they cover.

Summary of research done to examine WRB building code provisions and test methods and to perform independent laboratory testing to study WRB performance