In a given application, a vapor retarder can have opposite effects depending on its properties and conditions of use. Employed correctly, it can help keep structures dry, and when used incorrectly, it can contribute to moisture accumulation and prevent structures from drying. This creates a paradox of sorts because some vapor retarder materials like polyisocyanurate (ISO) insulation may be perceived as a problem. In reality, such materials can provide a simple and effective solution to water, air, vapor, and thermal control for building enclosures. The solution is proper application in coordination with the climate conditions and the overall design of any building envelope assembly (i.e. above-grade walls, below-grade basement and crawlspace walls, and roofs).
In the latest edition of a series of free, downloadable e-books, an article from the pages of The Construction Specifier explains how ISO insulation helps control moisture issues. To get your copy of Specifying Polyiso Insulation, in either pdf or digital edition, visit www.constructionspecifier.com/ebook/pima-specifying-polyiso-insulation-e-book.