October 1, 2007
Radiant Barrier Information
Radiant barriers are installed in homes to reduce summer heat gain through the attic, which helps lower cooling costs while increasing home comfort. See The Florida Solar Energy Center's Radiant Barrier FAQ for more information on the benefits.
Here's info I used to figure out the radiant barrier foil I installed in my attic - so far it's reduced the temp up there significantly, since installation it's not gone over 113F up there even with it getting up to 102F outside. I bought a wireless digital indoor/outdoor thermometer that I threw up in the attic to get the before and after temperature measurements. In May, it got up to 130F up there, now, it averages around 8 degrees higher than the outdoor temp on sunny days. It cost me $269 for the radiant barrier material with S&H and 4 sweaty mornings of my life. Right after installation my AC felt too cold upstairs - I had to readjust the air flow per wife's "orders". Different stuff you read says anywhere from 8% to 40% AC cooling savings, depends on how well insulated your attic and AC ducts in the attic are. For cold climates, you're supposed to put it on top of the insulation you have on the floor of your attic so you get both summer and winter savings (summer reflects sun heat away from your house, in the winter reflects house heat back into your house). Regardless of the climate, you should add another layer of insulation in your attic while you're up there (especially if it's blown in insulation).
Picture's worth a thousand words - so here's one vendor's graph on the results of installing their product and the temperature difference. Our results were similar.
SOURCE: www.RadiantGUARD.com
Lessons I learned the hard way (Warm Climate Installation)
- Do it in the winter when it's cool, or hire somebody stupid enough to do your labor in a hot attic (or wake up at 4 a.m. and plan two full weekends of being up there from 4-11ish - the more you get done, the longer you can stay up there - start on your south/east or SW facing side)
- Start at the top ridge and work your way down - running the foil horizontally (precut the length of your roof, plus ~4 feet - 2 feet each end) leaving a 9" gap below your ridge vent for ventilation (5" down the rafters on each side). Staple the strip only once at the top of the foil strip while you unroll it the length of your attic to the rafters - then from the middle staple it down the rafter and work your way out to each edge. It DOES NOT need to be airtight, but the more you cover, the more heat you reflect.
- Overlap the pieces half the length of your staple gun - from top of the roof to bottom, the last staple I put in the top piece is about the length of the staple gun - then when I staple up the next piece I staple the bottom sheet between the top sheet and the rafter - key is to capture the heat in the airspace between the rafter and the roof decking and ensure it naturally ventilates it's way out of your attic ridge vents.
- Add more insulation while you're up there, they recommend R39 in NC - I rolled unfaced insulation ontop of the existing blown in stuff (perpendicular to whatever already exists or the boards if blown-in)
- Check for HVAC leaks on your ducts while you're up there (need real duct tape to fix them - the kind made of metal not cloth, if you've a lot of sheet metal duct, buy some mastic and seal the seams with it) and look for gaps around any wires/pipes that go down into your house and fill them to stop air leakage from house to attic and vice versa using that expandable foam stuff.
- General goodies to know if installing this stuff yourself: Wake up with the sun and get up there early, wear old slacks and long sleeves and a face mask (old jogging suit windbreaker type fabric avoids fiberglass irritation - contractors powder themselves with baby powder on their exposed skin FYI), drink lots of water, plan on at least two weekends of 4-6 hours up there or hire some cheap laborers, use short staples in your staple gun not long ones (buy two boxes)
More Information
- What I bought: Ultra-Max Heavy Radiant Barrier Insulation 2000 sq. ft. ~ $269 inc S&H
Energy-Conservation-Specialists or AtticFoil.com - Nice Article on the entire concept and benefits
Health Goods Radiant Barrier Information - Gov't Radiant Barrier Attic Fact Sheet (Dated 1991)
Radiant Barrier Attic Fact Sheet - A more informative gov't read
Energy Efficiency and Renewable Energy Radiant Barrier Information Home Energy Magazine Radiant Barrier Article - Great installation photos and details
AtticFoil Installation Details
Installation Concept
Source: AtticFoil.com