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Attic Temperatures Are Often Higher Than Outside Air

When the sun shines on the roof of your house, the heat energy of the sun is absorbed by the roof into your home.

The darker your roof, the more heat is absorbed, and the more heat energy is radiated into your attic. It is possible for your attic to reach temperatures of 125 to 150 degrees when the outside air is 85 to 90 degrees.

That radiant heat will then heat your ceiling and warm up your living space, increasing your discomfort and making your air conditioning work harder. The most important thing you can do in your attic to keep your living space comfortable is to make sure you air seal and have adequate levels of insulation.

However, if you have any heating or cooling equipment or duct work in the attic, radiant barriers can be a cost effective investment by lowering the attic temperature and keeping your air conditioning equipment and duct work cooler.

What are radiant barriers?

Radiant barriers usually consist of a thin sheet or coating of a highly reflective material, usually aluminum, applied to one or both sides of a number of substrate materials. These substrates include kraft paper, plastic films,cardboard, plywood sheathing, and air infiltration barrier material. Some products are fiber reinforced to increase the durability and ease of handling. Usually the reflective coating is on one side of the radiant barrier. Sometimes it is on both sides.

How do radiant barriers work?

Not all heat energy that gets into your attic is from radiation. Some of the heat energy is from convection which occurs when attic air comes into contact with the underside of the hot roof. Some of the heat energy in your attic is from conduction when framing members are in contact with the hot roof deck. The radiant barrier works by reflecting the radiant heat energy coming into the attic from the roof back towards the roof and away from the living space.

How are radiant barriers installed?

There are three possible locations for a radiant barrier: roof radiant, attic radiant (1), attic radiant (2).

Each method has advantages and disadvantages:

Method

Advantages

Disadvantages

Roof Radiant

1. Top side of truss under the sheathing (between the sheathing and the truss)

1. Easy to install during new construction

1. Can’t be installed in existing house

Attic Radiant Method 1

1. Bottom of top cord

1. Protects barrier from dust which reduces its effectiveness.

2. Will protect ir handlers and ductwork in attic from radiant heat.

3. Easier to install in attics with truss construction than over insulation method.

1. Difficult to install in low-pitched roof houses.

Attic Radiant Method 2

1. Over insulation

1. Easier to install in low pitched roof houses

1. Subject to being covered with dust which reduces its effectiveness.

2. Harder to install with HVAC equipment and ductwork in attic.

How much can radiant barriers save me?

This varies with conditions: how well is your house shaded; how much insulation is in your attic; and if your air handler and duct work are in your attic. Studies from the Florida Solar Energy Center (FSEC) have shown that radiant barriers can save 8-12% of cooling costs. The amount of savings depends on how much of the heat load in your house comes from the attic. If the walls of your house are well-insulated and your windows are energy efficient, attic heat can account for a large part of the cooling load of your home, and radiant barriers can make a larger difference in your air conditioning bill.

Some radiant barriers can also be sprayed on.

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