Attic venting

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. It’s hard to screw up this approach. A vented attic works in hot climates, mixed climates, and cold climates. It works absolutely everywhere—when executed properly. Your local Austin, TX roofer will be able to answer your questions on the art of attic venting.

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. 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 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. In mixed climates, ventilation serves either role, depending on the season.

A key benefit of venting the attic is that the approach is the same regardless of how creative your architect got with the roof. Because the roof isn’t in play here, it doesn’t matter how many hips, valleys, dormers, or gables there are. It’s also easier and often less expensive to pile on fiberglass or cellulose insulation at the attic floor to hit target thermal resistance or R-values, than it is to achieve a comparable R-value in the roof plane.

The success of this approach relies on the ceiling of the top level of the house being completely airtight before any insulation is installed. It’s also important to ensure that there isn’t anything in the attic except insulation and air and not the plethora of crates and boxes. Attic space can be used for storage; however this works only if you building an elevated platform above the insulation. Otherwise, the insulation will get compressed or kicked around, which diminishes its R-value. An attic entry-way is also noted for being leaky and it will only continue to leak more the more often it is used.
Individuals that are not professional roofers get this approach wrong all the time by not following rules, punching holes in the ceiling to put in recessed lights which will leak air and a multitude of other no-nos. 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. It’s an energy waste no matter where you live.

Duct sealing is faith-based work. You can only hope you’re doing a good-enough job. Even when you’re really diligent about air sealing, you can take a system with 20% leakage and bring it down to maybe 5% leakage, and that’s still not good enough. With regard to recessed lights and other ceiling penetrations, it would be great if we could rely on the builder to air-seal all these areas. Unfortunately, we can’t be sure the builder will air-seal well or even air-seal at all. This leaves the responsibility in the roofer’s hands to come up with other options.

For all of your roofing questions, give you local Austin, TX roofer a call to discuss your venting needs.

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