Climate Zones and Attic Design
When you build or renovate, it’s important to consider your climate zone. The International Code Council defines different climate zones that provide guidance for energy efficient design and construction. The 2021 edition of the IECC includes updated definitions for climate zones that reflect current weather conditions and expected climate change over the life span of the building.
The new definitions for climate zones are more fine-grained and better aligned with NatHERS. The new definitions also take into account the influence of prevailing winds and the direction of incoming sunlight. The more you understand your climate zone, the more confident you can be about designing a home that will perform well over time.
Salt Lake City, Utah vented attic assemblies, Class II vapor retarders (see sidebar) should be installed in Climate Zones 6 and higher. This helps prevent condensation on ductwork from hot-humid climates, which can lead to “sweating” and mold growth on attic sheathing and framing members. Alternatively, the ventilation system can be designed to control moisture problems by allowing conditioned air to flow through the ductwork and into the attic space (i.e., a hybrid assembly).
Insulation Tips for Coastal Homes: Fighting Moisture and Salt Air
Venting or not venting an attic is a design and construction choice, not a requirement determined by the physics of a hygrothermal system. We conducted a parametric study to evaluate the effect of attic insulation thickness on the performance of ventilated and unvented attics. The results indicate that optimum attic insulation thickness significantly increases as the discount rate decreases, reaching about 60% lower NPP when compared with a conventional building in Climate Zone 1. In contrast, optimum wall insulation is about 50% lower NPP.
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