Radiant barriers: sucking dollars out of your NW project!

 This is from a series of guest posts by representatives of the Northwest Building Efficiency Center. This post was written by Gary Nordeen. 

Since the 1930s radiant barriers have shown to be beneficial in reducing cooling loads in structures located in hot climates. A radiant barrier is a material, usually aluminum, which is highly reflective and has a low emissivity. A material with low emissivity absorbs little radiant energy.

Radiant barriers are usually installed in attics to reduce radiant heat gains into the attic that are transferred into the living space. Radiant barriers can be installed on

the underside of roof rafters; laid on top of rafters or trusses prior to installing roof sheathing; laid flat on the ceiling insulation; or “chips” of reflective material can be added to the ceiling insulation.

Proper installation of the radiant barrier is important. Refer to Figure 1 at left, courtesy of Florida Solar Energy Center: 

• Applications #1 or #2 of sheet type radiant barriers are preferred to #3.

• Dust will accumulate if sheet type radiant bareriers are laid over the ceiling insulation.

• Chips or multi-layer radiant barriers are acceptable to be installed at location #3

Recently, there has been an effort to market radiant barriers in the Pacific Northwest with unbelievable claims of energy savings. One radiant barrier company has stated that their product can reduce energy bills by more than 50%. In hot southern climates, where radiant barriers work best, energy savings range from 2% to 10%. Tests by Oak Ridge National Laboratories have shown that the percentage reductions for winter heat losses are lower than those for summer heat gains.

While radiant barriers can reduce cooling costs, houses in the Pacific Northwest consume more energy for heating than for cooling. Before installing a radiant barrier to reduce heating costs, the following issues should be considered:

At times radiant barriers may actually result in higher heating bills.

When the sun is out on cool winter days, it provides some heating of structures by radiant heat transfer through the roof. A radiant barrier will negate some of these gains.

Radiant barriers may create moisture problems.

If placed on top of the ceiling insulation, a radiant barrier will get cold in the winter and may become a surface where moisture laden air escaping from inside the house may condense. This may cause the ceiling insulation to get wet and become less effective.

Investing in additional insulation and better windows, and stopping air leakage are proven methods to reduce your energy use. Be wary of any salesperson making exorbitant claims about reducing your energy bill. As the old saying goes: If it sounds too good to be true, it probably is.

Contact the Northwest Building Efficiency Center at Info@nwBuildings.org if you have questions about energy efficient buildings.