Arkansas HVACR NewsMagazine March 2026

HVACR NewsMagazine March 2026

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(practically speaking, 1 square foot of vent area per 150 square feet of attic area), but there is an exception. The minimum vent area could be as low as 1/300, so long as the following conditions are met: • If in Climate Zones 6, 7, and 8 , a Class I or II vapor retarder must be installed on the warm-in-winter side of the ceiling. Other climate zones do NOT require a vapor retarder by code. • No less than 40% and no more than 50% of the ventilation area (i.e., where vents are installed) shall be in the rafters or upper attic space (within 3 vertical feet of the ridge or highest point) EXCEPT in cases where wall or roof framing members conflict with vent installation. In those cases, vents are permitted to be installed more than 3 feet below the highest point. The remaining ventilation must be provided in the bottom third of the attic space.

How Attic Designs Need to Account for Heat and Moisture Bryan Orr HVACR School … Rick Sims’s “Conductsation” symposium session from a few years ago is one I keep coming back to time and time again because we see so many misinformed building designs in our market (Florida). His presentation contained a ton of great information about different causes of duct sweating in humid markets like Florida, but he had one particularly interesting point: ventilation design in unconditioned attics can either take advantage of natural air movement and cause little trouble, or they can dump moist air into the attic and make it rain on the ducts and air handlers (in attic installations). If an attic is NOT in the thermal building envelope (i.e., if it’s not conditioned), ventilation is required per the latest International Residential Code (IRC). The IRC lays out requirements for vent area and placement in R806.2, and this code helps us design vents in ways that take advantage of heat and moisture’s natural movement to prevent water vapor from condensing on duct surfaces — and potentially causing bigger

structural problems. The IRC’s Guidance

Section R806 of the 2021 IRC covers roof ventilation practices, with R806.1 laying out the basics for vent opening sizes and screening materials for protection from the elements and animals — not particularly interesting for our purposes.

• We’re based in the humid part of Climate Zone 2 (but some of South Florida is in Climate Zone 1), so the vapor retarder condition doesn’t apply to us. However, that second condition matters a lot. Placing the vents outside the locations indicated in the code — or with the improper venting area in each location — can directly contribute to duct and air handler sweating in attics.

However, R806.2 sets forth the minimum ventilation area requirements. The general requirement is 1/150 of the vented space