![]() ![]() The air leakage from these holes and systems is a major cause of ice dams in cold climates and a major cause of humidity problems in hot climates. They punch a bunch of holes in the ceiling, they fill the holes with recessed lights that leak air, and they stuff mechanical systems with air handlers and a serpentine array of ductwork in the attic. How do people get this simple approach wrong? They don’t follow the rules. You can build an airtight entry to the attic, but you should know that the more it is used, the leakier it gets. Also, attic-access hatches are notoriously leaky. Otherwise, the insulation gets compressed or kicked around, which diminishes its R-value. Attic space can be used for storage, but only if you build an elevated platform above the insulation. (See “Attic-Insulation Upgrade” in FHB #200.) It’s also important to ensure that there isn’t anything in the attic except lots of insulation and air-not the Christmas decorations, not the tuxedo you wore on your wedding day, nothing. The success of this approach hinges on the ceiling of the top level of the house being absolutely airtight before any insulation is installed. It’s also easier and often less expensive to pile on fiberglass or cellulose insulation at the attic floor to hit target R-values than it is to achieve a comparable R-value in the roof plane. Because the roof isn’t in play here, it doesn’t matter how many hips, valleys, dormers, or gables there are. ![]() ![]() In mixed climates, ventilation serves either role, depending on the season.Ī key benefit of venting the attic is that the approach is the same regardless of how creative your architect got with the roof. In a hot climate, the primary purpose of ventilation is to expel solar-heated hot air from the attic or roof to reduce the building’s cooling load and to relieve the strain on air-conditioning systems. (See “Energy Smart Details” in FHB #218 for more on ice dams.) In a cold climate, the primary purpose of ventilation is to maintain a cold roof temperature to avoid ice dams created by melting snow and to vent any moisture that moves from the conditioned living space to the attic. The intent of roof venting varies depending on climate, but it is the same if you're venting the entire attic or if you’re venting only the roof deck. I'll also explain when it makes sense to move the thermal, moisture, and air-control layers to the roof plane, and how to detail vented and unvented roofs correctly. Here, I'll explain how to construct a vented attic properly. Unfortunately, we manage to screw it up again and again, and a poorly constructed attic or roof assembly can lead to excessive energy losses, ice dams, mold, rot, and lots of unnecessary homeowner angst. It works absolutely everywhere-when executed properly. It works in the Arctic and in the Amazon. A vented attic works in hot climates, mixed climates, and cold climates. So I'll start by saying something that might sound controversial, but really isn't: A vented attic, where insulation is placed on an air-sealed attic floor, is one of the most underappreciated building assemblies that we have in the history of building science. So much information has been devoted to the subject of roof venting that it's easy to become confused and to lose focus. ![]()
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