QUESTION: Our house is hot and I can feel the heat radiating down from the ceiling even though it is well-insulated. Will putting reflective foil in the attic help much and what is the best way to install it myself?
ANSWER: Putting reflective foil under your roof is one of the most effective methods to reduce the heat buildup in your home and cut your air-conditioning costs. With adequate attic ventilation, it can significantly lower the temperature of your ceiling. You can often feel the difference in your rooms.
Although standard fibrous attic insulation, like fiberglass, blocks conductive heat loss in the winter, it is not very effective at blocking the radiant heat from a hot roof in the summer. The insulation itself gets warm and the heat comes right through into your living area.
Heavyweight aluminum foil or reinforced foil are excellent materials to use. The aluminum is reflective, so some of the roof's heat is reflected away from your ceiling.
The primary heat reduction property of aluminum is that very little heat is reradiated from the shiny underside to the insulation and ceiling below. With adequate attic ventilation, much of the heat is carried away.
For greatest heat reduction in the summer, install the reflective foil on the underside of the roof rafters. This leaves an air gap above and below it, which is necessary for its reflective properties to be effective.
Although it sounds strange, if you install single-sided foil (kraft paper on one side), face the shiny side down, away from the roof. This reduces the radiant heat flow to ceiling.
Some recommend just laying the foil across the top of the insulation on the attic floor. This may cause potential moisture problems in the insulation and dust on the foil surface may reduce its reflective properties.
The easiest do-it-yourself method to apply the foil to the bottom of the roof rafters is with a heavy-duty stapler. Be sure to leave adequate gaps for ventilation at the edges. Start it on the rafters several inches above the insulation and leave a several-inch-wide gap at the peak of the roof.
There are many manufacturers and types of reflective foils and the prices vary from a low of about 13 cents per square foot to several times that much. Make sure to get a material that is strong enough to hold up. It can be just heavyweight foil, or be reinforced with film or fibers.
You can write to me for Utility Bills Update No. 070, showing a list of manufacturers of reflective foils, instructions and diagrams for installing it yourself, and a small sample piece of reflective foil. Please include $1 and a self-addressed envelope. Send your requests to James Dulley, c/o Los Angeles Times, 6906 Royalgreen Drive, Cincinnati, Ohio 45244.
No Matter How Sliced, Toast Energy the Same
Q: I have a large family and I was wondering if it is more energy efficient to use a two-slice or a four-slice toaster in the morning? They really eat a lot of toast.
A: With most kitchen appliances, it is better to make larger quantities of foods at one time. However, toasters are an exception. It doesn't really make much difference other than the fights over the first few slices.
Toasters brown the bread with radiant heat from the red-hot elements instead of cooking or baking it. Therefore, the residual heat in the toaster from adjacent slots does not toast the bread any faster.
Letters and questions to Dulley, a Cincinnati-based engineering consultant, may be sent to James Dulley, Los Angeles Times, 6906 Royalgreen Drive, Cincinnati, Ohio 45244.