House & Home: Heat Blocking Attic Foil

By James Dulley

Ways to keep cool for cheap.
by James Dulley

From afternoon well into the evening, I can feel heat blasting down from the ceiling into the house. Our air-conditioning bills are outrageous. On a limited budget, what can I do to stop the heat? – D. E.

 A hot roof literally becomes a blast furnace making you uncomfortable, pushing up your electric bills and wearing out your air conditioner. A typical dark roof can reach 150 degrees in the afternoon, and it holds this heat well into the evening. Adding more attic insulation will not help. It may actually make the problem worse by absorbing and holding the heat longer.

Installing do-it-yourself radiant barrier attic foil or special new water-based reflective paint on the underside of the roof is effective. Foil blocks 95% of the radiant heat from the hot roof. I installed it in my attic and it dropped my bedroom temperature by 10 degrees.

Attic radiant barrier foil is basically the same type of aluminum foil that you use in your kitchen. For durability and easy installation, attic foil is thicker and reinforced with nylon mesh or kraft paper.

Attic foil is very easy to install. Simply staple it to the underside of the roof rafters. The neatness of the job is not important for it to be effective. It took me about two hours to do a 30 ft. by 50 ft. attic. Do it in the evening or in the early morning when it is cooler.

The lightweight aluminum foil is often available in four-foot wide rolls from 50 to 100 feet long. Start stapling at one end near the roof peak and work your way down with each successive strip.

Overlap each strip several inches. Stop several inches above the attic insulation. This gap is important to allow air in the attic to be drawn up between the underside of the roof and the top of the foil.

Heat reflective silver paint, Lomit-II, has many of the heat-rejection properties of aluminum foil. It is sprayed, brushed or rolled onto the underside of the roof sheathing. It is quick to apply since it is not important how neat the job looks. For the foil or paint to be most effective, install vents near the peak of the roof to exhaust this hot air. Because this air is hot and less dense, it naturally flows upward and ventilates your attic without fans.

If you do not have vents near the roof peak, install do-it-yourself ridge vents. Many ridge vent kits are available in rolls or strips and are only several inches high, barely noticeable from the ground.

Download (from Update Bulletin No. 411 – buyer's guide of 20 manufacturers of do-it-yourself attic foil, heat-blocking attic paint, ridge vent kits, prices and installation instructions for a radiant barrier, installation instructions for a roll-out shingle over a ridge vent, safety tips for installing an attic radiant barrier system, sizing chart for area of foil needed. $3. Send questions to James Dulley c/o


This article was originally published on April 30, 2007.