There’s nothing better than a bright summer day in Maine, especially when the air is crisp and dry. Memories of five months of winter recede as the warmth you’d almost given up on suffuses through you, and you realize, blissfully, why our state motto is “The Way Life Should Be.”
If only it ended there. Unfortunately, the warm weather we adore by day can create serious discomfort by night. As you climb the stairs to your top-floor bedroom, you’re getting closer and closer to an attic that’s been warming up all day, storing heat to radiate back to you all night long. Add humidity to the mix and your night will certainly be less than restful.
No wonder so many of us rush to the store and snap up the air conditioners and window fans at the first sign of humid tropical air coming up from the south. No wonder our electrical bills spike in the summer months. No wonder we sometimes lie awake at night, feverishly pining for autumn’s return.
Life doesn’t have to be this way. There are plenty of short-term fixes – from scanty pajamas to an army of fans – but a real solution takes building science. First you need to understand what’s making you so uncomfortable:
Radiant heat: Suffice it to say that sunlight does indeed warm up your house. Daytime temperatures on your roof deck can exceed 140ºF, especially if your shingles are dark. At night, when temperatures usually drop, that absorbed heat is released. If your attic insulation is ineffective, you’ve got a giant low-grade radiator hanging over your head, providing that sauna you’ve been wanting. If you live in a Cape-style home, chances are your sloping sidewalls and knee-wall attics are also uninsulated, which provides a few more radiant surfaces for your enjoyment.
Airflow: The old adage says that heat rises, but the truth is that heat will flow anywhere it’s enticed to go by a difference in air pressure. In winter, cold air (which is more dense) wants to push in through tiny leaks and cracks in the lower parts of your heated home, which drives the warm air up and out through similar holes and seams in the upper sections of your house. In the summer, this “stack effect” reverses: cool air in your home seeks to get outside through leaks in the basement and rim joists, which pulls that hot attic air inside any way it can – through cracks in the ceiling, ventilated recessed lights, even the joints in your attic where wall studs and beams meet sheetrock or plaster. These little highways of hot air are delivering carloads of unwanted visitors to the inside of your home, and they’re dancing on that hot ceiling you’re staring at.
Ventilation: Fog and marine weather make ventilation tricky in Maine, but the general rule can be summed up in one ratio: one square foot of ventilation for every three hundred feet of attic space. With so many different types of vents in common use (ridge, gable, soffit and roof), it’s not uncommon to find an over-ventilated roof.
Radiant heat, excessive airflow, and over-ventilation may conspire to ruin your idyllic Maine summer, but there is a solution, and it comes with a classic building science catchphrase. “Seal tight, ventilate right” sounds easily enough, but while it’s relatively simple to describe, it’s painstaking to effect in reality. Here’s why:
Seal tight: There’s no stopping the sun’s warmth (which is probably a good thing), so building science focuses on keeping the heat that builds up on your roof from making its way into your living space. A strong “building envelope” comprised of thorough air sealing and effective insulation will separate inside from outside and do the trick nicely.
Sealing air leaks (aka “hot air highways,” or “chases,” in building science-speak) will stop the stack effect. The vast majority of these leaks are in your attic and basement, and whether you’re using expanding foam, mastic, or caulking, blocking those chases is essential if you’re going to keep the unwanted air, cold or hot, out of your living space.
Insulating with blown-in cellulose will reinforce this air sealing and add an effective layer between you and that hot, steamy attic. (Before you DIY this step with batts of the pink stuff, remember that fiberglass insulation has a lot in common with its cigarette filter cousin. Both let air flow freely, which is exactly what you’re trying to avoid.) In contrast to the pink stuff, cellulose is 100% recycled (very often you can see the letters still on the tiny squares of newsprint in it), non-toxic, and insect-repellent, thanks to the addition of boric acid. Packed densely into the sloping sidewalls on a Cape, it does of great job of keeping the upstairs cooler in the summer and warmer in the winter.
Ventilate right: Optimizing your attic’s ventilation can help the insulation up there perform at its best, and can even help your roof deck last longer. More is not necessarily better, so don’t just crack a window and call it good.
Summer doesn’t have to mean choosing between sweltering nights or the glacial cool of an air conditioner eating a hole in your family’s budget. Life in Maine can live up to its billing, but there’s often a bit of work involved. If we get the air sealing, insulation and attic ventilation done right, there’s no reason we can’t all sleep better through the summer months, enjoying the pleasures of the season instead of dreaming of the return of cooler weather.
Cree Hale Krull is a Building Performance Institute-certified Building Analyst and an Energy Advisor for Evergreen Home Performance. Cree helps homeowners cut energy waste, improve comfort, and maintain dry, healthy basements with customized insulation, air sealing, and encapsulation projects.