As attic spaces vary in dimensions and configurations, the types of attics—conditioned or unconditioned, habitable or not, vented or unvented—can vary just as much. For many people, attics serve as repositories for seasonal decorations and seldom-opened boxes of memorabilia; what homeowners may not realize is how they factor into warm-weather cooling. Consultation with your architect can help determine what type of attic you have and how it's impacting your energy bill during those summer months.
Even in homes with flat roofs, there’s likely to be at least some semblance of crawlspace between the roof and the ceiling of the living area beneath it. You may find, after donning a facemask and putting fresh batteries in your flashlight, that your attic is surprisingly spacious. Or you may find nothing but insulation between the ceiling joists, and little room to maneuver. A quick visual inspection is a good first step; an architect can confirm your suspicions later.
Conditioned attics have the bulk of their insulation at the roof deck assembly, and share air conditioning infrastructure with the rest of the house to stay climate controlled. Conditioned attics are usually conditioned because they’re habitable: They might have roof pitches overhead that allow seven feet of unobstructed, vertical standing room, and a staircase or built-in ladder for access. These spaces may include family rooms or additional sleeping quarters, often with built-in storage behind knee walls. If you’re considering converting an unused attic into a conditioned space, be sure to consult with an architect to ensure that both your home’s structure and its systems can support the loads of additional live occupancy.
Unconditioned attics—perhaps the most basic configuration—rely on airtight seals at the attic floor level, with thick, high-density insulation forming a blanket upon the attic floor. This helps to keep your house’s conditioned air from mixing with seasonally variable temperatures of the attic air. Think of your house in the summer as being like a thermos full of iced lemonade. Inside, your HVAC system acts as the ice cubes cooling the interior. Outside, the sun is shining on the roof and heating it up. Your attic might be hot, but if your roof and ceiling are both airtight, none of that warm air will make it into the cool interior of your home.
A common misconception is that if your attic is hot, you might be wasting energy spent on cooling your home; there are lengthy debates to be had about the efficacy of attic fans for ventilation. But the hot air in your attic during the summer months actually tends to stay there; if your upper level is too hot, that is more likely to be caused by a problem with the HVAC system. That said, it's a good idea to run a thermography test to ensure there isn’t air leakage between your attic and the floor beneath it; otherwise, a powered attic fan might pull cool, conditioned air into the attic, turning what you thought was an energy-saving measure into one that instead increases energy consumption.
Regardless, smart homeowners should pay more attention to their attics. If you have standing room available, it might hold potential to add more usable square footage to your house. At the very least, contact an architect to fully understand your attic, so that the summer sun beating down doesn't lead to a subsequent beating on your energy bills.
About the author: Deane Madsen, Assoc. AIA, is a writer and architectural photographer based in Washington, DC. He is the founder of Brutalist DC and the former associate editor of design for Architect Magazine.