Irc Faq Conditioned Attics

High performance housing faq 2009 irc conditioned attics this information sheet has been prepared by building science corporation for the department of energy s building america program a private public partnership that develops energy solutions for new and existing homes.

Irc faq conditioned attics. The irc has permitted unvented conditioned attics since 2006 with certain requirements. A passageway for conveying water vapor from an unvented attic to the. Habitable attics require a vertical access and emergency escape and rescue opening. However if moisture is able to enter the unvented attic space it may lead to roofing panel issues.

Code requirements vary across the country. Air permeable insulation is typically fiberglass cellulose or low density. Attics that meet the size and ceiling height criteria of the habitable attic definition in chapter 2 are considered habitable. The roof deck in an unvented attic must be exceptionally airtight.

2015 irc section r202 definitions vapor diffusion port. Unventilated attics can help to mitigate energy loss through leaky ducts or ceiling fittings. The acceptance of unvented conditioned attics continues to grow among builders and building officials. They come with their own set of drawbacks according to your own estimates this fundamental design flaw is costing you 1 000 a year.

The irc also prohibits a vapor retarder on the attic floor of conditioned attics so that any moisture that may build up in the attic can dissipate into the house. If wood shingles or shakes are used a inch air gap must be left above the roof sheathing but below the shingles or shakes and roofing felt. For example if an r 80 unvented cathedralized attic is to be constructed in a cold climate a minimum of r 40 50 should be air impermeable insulation installed and layered according to section r806 5 of the 2012 irc figure 4. For you the investment in insulation to create a conditioned attic isn t worth it because the payback period is 7 years.

The 2009 and 2015 irc verbiage is similar and still applicable. Design specifications of air supplied to the conditioned attic. 2 air permeable insulation only irc r806 5 5 2 attic while the irc refers to this assembly as air permeable insulation only it also involves installation of rigid board insulation above the roof sheathing. The energy savings touted by unvented attics can be as high as 20.

Section r806 5 unvented attic and unvented enclosed rafter assemblies. But conditioned attics are not unalloyed blessings.