How to Cool off your attic this summer
Natural Ventilation Is Good for Your House
You might think an uninsulated garage is the hottest part of your Arizona house in July and August, but actually the area where you are more likely to suffer heatstroke is in an unventilated attic where it can reach 160 degrees or more on a scorching summer day.
That kind of heat in the attic can drive up a home's utility bill and also fry and damage the underlayment of the roofing that sits on top of the attic.
So, homeowners often call to ask how to deal with this issue: Should they install more insulation overhead? Should they put a ventilation fan in the attic?
When it comes to insulation, if your home is fairly new and has R-38 rated insulation in your attic, you probably don't need more attic insulation or things like radiant barriers, for example.
Use Vents, Not Fans, and Let the Wind Do the Work
Although some might disagree with us, at Rosie on the House, we tell homeowners not to install those power fans either. That's because the only thing an attic fan will do for you – whether the fan is solar or electric-powered - is create negative pressure in the attic. That will pull the air-conditioned air from down below in the rest of the house up into the attic. That also means your AC will work harder than ever to cool you off downstairs. The fan that was supposed to help cool your attic is actually stealing that coolness away from your house where you want it to be.
You do want to install, if you don't already have it, a system of passive vents that can reduce heat in the attic by using the natural force of the wind. Most recently built homes have this type of system.
We recommend placing intake vents at the roof's edge or in the soffits, under the eaves of the roof. Make sure attic insulation isn't covering the eave or soffit vents. Otherwise, fresh air can't enter your attic.
Place the exhaust vents in areas of negative pressure high on the roof at or near the ridge. Those ridge vents can create continuous airflow through the attic. You can also use louvers, covered openings on the gables that allow air to escape the attic.
Although power fans are a bad idea, you can also install turbine vents – sometimes called whirlybirds – spinning "wheels" mounted near the ridge or ridges of the roof. These devices can extract warmth from inside the roof as the small fins on the turbines start rotating when the wind blows.
If you have proper passive ventilation in your attic, you will prolong the life of your roof, and you may put a little less stress on your air conditioner as well.
Some innovative builders also install venting while building homes with flat roofs. They install vents outside to protect the insulation that may be overhead in your ceiling.
A Final Word About Your Attic
Remember, regardless what temperature your attic space is – 140, 150 or 160 degrees – if you are close to having R-30 or R-38 insulation above your ceiling, the attic temperature in the middle of the summer only adds about 10 percent to your cooling bill. That means it's 5 percent of your total electric bill.
For the average Arizona home, that's about $15 a month, and it's only in the hottest summer months. So, you could say that the average Arizonan only pays a total $45 to $60 a year for cooling due to excessive heat in the attic.
And yet we know people who will gladly spend thousands on powered attic vents, unnecessary additional insulation, or practically worthless radiant barriers. What kind of return on investment are you getting when you pay $2,000 to save yourself $50 a year for 40 years? Trust me, there are much more lucrative investments that you can make to save on your cooling bill in summer.
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