Foam plastic insulating sheathing (FPIS) products come in many thicknesses to accommodate almost any end use and can be used along with approved tapes 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.

Top Resources:

Tools & Education

Wall Calculators

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.

Water, Water Everywhere and Not a Drop to Drink: Practical Building Science to Keep Walls Dry

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

FACTS: Moisture Control for Wall Assemblies

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.

Best Practices

Window Installation: Pan Flashing and Air-Sealing to Prevent Water Intrusion

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.

Window Installation with FPIS and Wood Framing

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.

Construction Guide: Next Generation High Performance Walls

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

Model Moisture Control Guidelines for Light-Frame Walls: A Building Code Supplement for Builders, Designers, & Bldg Officials

This Research Report provides actionable guidelines to effectively consider, evaluate, and manage the balance of wetting and drying potential in common above-grade, light-frame wall assemblies in a broad range of climate conditions. 

Additional Information

Moisture Control for Frame Walls - Code Compliant Wall Detailing

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

Guidance on Taped Insulating Sheathing Drainage Planes

This guide provides information and recommendations to the following groups: insulation contractors; general contractors; builders; home remodelers; mechanical contractors; and homeowners.

Continuous Insulation and Punched Openings Windows Can Be A Pain

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

Building Science Insights: Leaks and Holes

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

Building Science Insights: Stuck On You

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.

Water-Resistive Barriers: How Do They Compare?

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