NFPA 285 testing is an assembly test but the specific need for NFPA 285 testing is a function of the materials selected, which edition of the code is in use, and the acceptability of engineering judgement letters by both the design professional and the AHJ. Complicating the matter is there is no centralized list of accepted/tested assemblies, such as UL, to serve as a point of reference and most projects cannot afford the time or cost of specific NFPA 285 testing.
For example, the code requirement to test weather resistive barriers and high pressure laminates first appeared in IBC 2012, while the requirements for foam plastic date back to 2000 (and even earlier under the UBC).
Wall detailing has become increasingly complicated not just by the codes but by the multitude of product choices we must make. Weather resistive barriers (WRB) can be non-adhered sheets, adhered sheet membranes, or fluid applied membranes. The performance of these products are not
equivalent and are not appropriate for all projects. Add to the mix that contractors and installers (and designers) can lack basic knowledge in installation of the specific products used.
I suggest:
- Confirm the basis of individual manufacturer claims of NFPA 285 compliance. (tested assembly, engineering judgement, or alternate compliance path)
- Verify your local code and jurisdictional requirements.
- Design for redundancy (use sheathing with a WRB) and durability (durable design is sustainable design). Consider mechanisms for failure; what happens when that WRB is punctured by a fastener? What is the reduction in R-value for wet insulation? Are adjacent materials compatible in short and long term?
- Select products with a proven record of performance (see durability). Understand your clients, and your own, tolerance for risk.
- Verify compliance of the installed product.
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David Bliss AIA
Simpson Gumpertz & Heger
Waltham MA
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