Tips to keep your attic cool
By Marc Richmond*
Picture this: It’s a hot and humid summer day. You head for the indoors and some relief from your trusty air conditioning (A/C) system. Three hours later, you’re slightly cooler, but you’re wondering why your A/C unit hasn’t shut off yet. Here’s why: all day long, solar radiation has been heating up your home through the windows, walls, doors and especially the roof. Your attic temperature can easily reach over 140 degrees. That heat up there is working its way through your meager attic insulation into your home and through the A/C ductwork, located in your attic, into your cooling system. Your A/C system has to fight that added heat to change all that hot air in your home into cool air. You can install solar screens for the windows, porches around the house for shade, and plant trees around the home, but what do you do about the roof which accounts for a third of all the heat build-up of your house?
Here are a few options:
Ventilate your attic with ridge and soffit vents. Vents are louvers, grills, or screen materials which allow passage or air through them. They are typically installed along the top peak (ridge) of your roof, at the top of the side wall (gable), and on the underside of your roof overhang (soffit). Ventilation moves air through your attic by force of wind or by heat rising through natural convection. This leaves cooler air sitting on top of the insulation on the attic floor. Ventilation also has the ability to remove humidity which has built up in your attic and which reduces the effectiveness of your insulation. It is often best to hire a contractor to install these.
Insulate your attic to R-30. R-30 is roughly a 10 inch thick layer of insulation material above your ceiling. This is a job for any handy homeowner or it could be handed over to a contractor. When installing the insulation, be careful not to block your vents.
Install a radiant barrier between your roof and your attic insulation. A radiant barrier is an aluminum foil material which prevents 95 percent of the heat that radiates from your roof from reaching the insulation on your attic floor. It comes in a roll and is stapled to the underside of your roof rafters, or as a metallic paint. Radiant barriers are sold in most building material supply centers and can be easily installed by a homeowner. This system can save you up to eight percent on your summer cooling bills.
When it comes time to replace the roof, use roofing material which resists or reflects heat – typically lighter colors are best, though there are some new materials which are effective at reflecting infrared radiation (heat) with a more ‘traditional’ color.
This article first appeared in the Austin American Statesman and was republished by us in 1997. *We have since edited the article. At the time of publication, Mr Richmond was with the City of Austin’s Green Building Program; he now is president of Practica Consulting.
