Using Polyiso as a multi-functional solution
For many, the id0ea of eliminating a second layer of protection may be daunting. However, the use of polyiso insulation as a WRB is not a new practice. When NoHo West, a mixed-use community in North Hollywood, California, was undergoing revitalization construction in 2019, the building owner and architect decided to design and remodel the new development to comply with the 2020 California building code, which requires ci in new structures. The project design and budget required value engineering to reduce costs and improve the construction schedule.
Table 1: Assessment of Water-resistive Barriers (WRB) Water Penetration Test Criteria per ASTM E331
| WRB Material | Test Condition |
| No. 15 Felt, lapped seams | 13.7 kg/m2 (2.8 psf), 15 minutes |
| Polymeric housewrap, lapped seams | 13.7 kg/m2 (2.8 psf), 15 minutes |
| Polyiso foam sheathing, sealed joints | 30.4 kg/m2 (6.24 psf), 2 hours |
To reduce the project’s overall carbon footprint, per the new code requirements, and still meet deadlines and budget constraints, the design and construction team considered alternative options for the wall assembly. The original design included a WRB membrane over the continuous wall insulation. However, when the exterior wall system subcontractor suggested using an exterior polyiso ci as the WRB, it eliminated the sheet applied WRB in favor of sealing the board joints of the polyiso boards. A third-party testing company’s jobsite inspection confirmed that the use of polyiso as the WRB was acceptable and met all requirements.
In choosing a solution capable of serving as both ci and a WRB, the team effectively reduced material and labor costs while shortening the construction timeline. This multi-functional solution also helped to reduce the project’s environmental impact by using fewer construction materials and creating less waste, and, by increasing the overall energy efficiency of the completed building, it helped to meet the project goal for building code compliance.
Achieving high-performance protection, efficiencies, and peace of mind
As budgets tighten and construction timelines shorten, building materials can help address these challenges effectively by being adaptable to project needs. In addition to being a practical and effective WRB, polyiso continuous wall insulation provides superior thermal resistance to help ensure long-term energy efficiency within the building envelope.
Long-term protection and safety are a priority for any project. Unlike other foam plastic insulations, polyiso is a thermoset material which chars in place if subjected to open flame, which helps to reduce the rate and severity of fire growth. Several manufacturers offer polyiso insulation products that the National Fire Protection Association (NFPA) has approved in many of its compliant wall assembly solutions in NFPA 285-Standard Fire Test Method for Evaluation of Fire Propagation Characteristics of Exterior Wall Assemblies Containing Combustible Components. This offers building professionals flexibility and certainty when designing fire-resistant structures.
