Often overlooked, radiant heat is the largest source of heat gained by a typical building. This is the type of heat you feel when you are out in the
direct sun. Several institutions report that over 90% of the heat gained by a typical house is in the form of radiant heat gain. The sun can heat a typical
dark colored roof to temperatures exceeding 190 degrees. Much of this heat conducts through the roof structure and is emitted into the attic space below.
If you have ever been in an attic during a sunny day, you have felt the results of this radiant heat. Attic temperatures in the south are typically 140
degrees or higher throughout the summer.
Adding a radiant barrier to the attic is one of the best ways to combat this radiant heat gain. When stapled up to the roof joists, this heat reflecting
foil can reduce attic temperatures by 30 degrees. More importantly, it stops the direct radiant heat which otherwise penetrates ceiling insulation and ends
up heating the space below. In fact regular mass type insulation does little to stop radiant heat.
There are several different types of radiant barrier products available. For use in an attic, you will want to find a material that is perforated, durable,
and double sided. The perforations are small holes punched in the foil to allow moisture to pass through. This allows the material to "breath" and reduces
any chances of accumulating moisture in the attic space. The material must be durable to hold up to stapling and harsh attic conditions. A double sided
radiant barrier has aluminum on both sides of the material. The shiny surface will reflect heat on the hot side like a mirror. The aluminum surface facing
the cold side is important because aluminum does not easily reemit heat to the air below. If fact the low emmisivity value of Aluminum (0.03 to 0.05) means
that only 3% to 5% of the radiant heat will be reemitted to the air on the cold side.
Installing radiant barrier in an attic can be a bit of a project, but with the proper tools and information any handy person can do the job. Remember when
working in an attic that you must be careful where you step. The drywall will not support your weight, so stand only on ceiling joists. Also, be careful
when working around electrical lines. The radiant barrier generally comes on a roll. Typical roll sizes are 48 inches wide by 250 feet long and weigh 30
lbs. Cutting the roll into strips on the ground and rolling them back up into small lightweight rolls generally makes the material easier to handle in the
attic. In a conventionally framed attic, it is recommended installing the strips perpendicular to the direction of the roof joists. This way you do not
have to worry about lining it up with the joists, or stapling in the edge of the material. Start at the bottom leaving a 2" space above the insulation and
work your way up the roof. You should overlap each run by about 2" and staple in place. The area directly below any roof vents should be left open to help
ventilate the attic space.
After you have finished installing the radiant barrier you should notice an immediate difference in the comfort of your home. Your house won't heat up as
quickly in the mornings. Your attic will be cooler, and you won't feel heat coming down from the ceiling. Also, installing radiant barrier in an attic can
reduce your cooling expenses by 10% to 25%. Often, when you install the material yourself, it will pay back in electricity savings within a year. With electric
prices constantly going up, it is time to start improving the efficiency of our homes.
© 2006 Dan Walter
Energy Efficient Solutions
115 N Capri Dr
Duncanville, TX 75116
Note: This article was submitted by a second party and the contents are subject to our disclaimer.