{"id":115029,"date":"2020-07-02T09:15:05","date_gmt":"2020-07-02T13:15:05","guid":{"rendered":"https:\/\/www.constructionspecifier.com\/?p=115029"},"modified":"2020-06-30T16:19:03","modified_gmt":"2020-06-30T20:19:03","slug":"new-ibc-rules-for-insulation-in-unvented-enclosed-roof-framing-assemblies","status":"publish","type":"post","link":"https:\/\/www.constructionspecifier.com\/new-ibc-rules-for-insulation-in-unvented-enclosed-roof-framing-assemblies\/","title":{"rendered":"New IBC<\/em> rules for insulation in unvented enclosed roof framing assemblies"},"content":{"rendered":"
\"Photo<\/a>
Photo \u00a9 BigStockPhoto.com<\/span><\/em><\/figcaption><\/figure>\n

by Anthony J. Nicastro, PE, and Megan A. Toumanios, PE<\/strong><\/p>\n

Low-slope and steep-slope unvented roof systems (i.e.<\/em> 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, architects of these \u2018compact\u2019 roof assemblies must consider vapor permeance and arrangement of the materials to produce acceptable hygrothermal performance and low risk of condensation in the resulting conditioned \u2018attic\u2019 space. To this end, the 2015 version of the International Building Code<\/em> (IBC<\/em>) includes new provisions that relate to unvented enclosed rafter\/truss assemblies and unvented attics. These rules, especially in section 1203.3, \u201cUnvented attic and unvented enclosed rafter assemblies,\u201d dictate how design professionals specify vapor retarders and placement of insulation in compact roof assemblies for moisture control.<\/p>\n

Most requirements for roofing and thermal efficiency in IBC<\/em> are contained in Chapter 13, \u201cEnergy Efficiency,\u201d or Chapter 15, \u201cRoof Assemblies and Rooftop Structures.\u201d However, Chapter 12, \u201cInterior Environment,\u201d addresses, among other topics, ventilation and temperature control. Further, the relationship of unvented attic spaces to maintaining the interior environment through use of insulation is also discussed in Chapter 12, a section seldom associated with roofing materials. Insulation requirements for roofs are, therefore, spread across IBC<\/em> Chapters 12, 13, and 15.<\/p>\n

Applicable roofing assemblies<\/strong><\/p>\n

Designers may view unvented \u2018attic\u2019 (i.e.<\/em> attic space, enclosed rafter, or joist space above normally occupied and conditioned interior space) assemblies as an economical arrangement of roofing and insulation materials. However, insulation placement in roof assemblies requires careful review to achieve acceptable hygrothermal performance levels and limit the potential for condensation within the system. Recent IBC<\/em> changes to section 1203.3 recognize successful arrangements of insulation with respect to permeable and impermeable materials, providing design directive to help limit potential failure due to condensation.<\/p>\n

\"Figure<\/a>
Figure 1:<\/strong> Roof insulation configurations for unvented rafter\/truss assemblies.<\/span>
Images courtesy Simpson Gumpertz & Heger<\/span><\/em><\/figcaption><\/figure>\n

IBC<\/em> dictates acceptable placement and composition of roofing materials in Chapter 15, but describes required thermal efficiency of the roof in Chapter 13, which references the International Energy Conservation Code<\/em> (IECC<\/em>). The minimum required thermal resistance varies depending on insulation placement relative to other materials. Possible locations for insulation within the roof assembly, as addressed by IBC<\/em>, include:<\/p>\n