Tag Archives: Vapor retarder

New IBC rules for insulation in unvented enclosed roof framing assemblies

Unvented roof systems, where the insulation and air barrier are applied directly to the underside of the roof deck, are common in applications where designers are seeking cost-effective and energy-efficient roof assemblies. However, designers of compact roof assemblies must consider vapor permeance and arrangement of the roofing materials to produce acceptable hygrothermal performance and low risk of condensation in the conditioned attic space. To this end, the 2015 version of the International Building Code (IBC) includes new provisions relating to unvented attic and unvented enclosed rafter assemblies that dictate how designers specify vapor retarders and placement of insulation in compact roof assemblies for condensation control.

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The air/vapor barrier must die

As manufacturers introduce materials with new properties and attempt to push the boundaries of building envelope construction, it is crucial the industry agrees on terminology for communicating the specific functions and purpose of these materials to avoid confusion and costly errors. In this regard, the term ‘air/vapor barrier’ is misleading and should be replaced with more appropriate terminology.

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