Radiant barriers are a relative newcomer to the area of residential insulation. All radiant barriers are based upon space age technology. In 1954 NASA developed this material which we now call a "space blanket". This "sheeting" covered with deposited aluminum helps reduce heat transfer, which is vital in the cold of space. The same technology used by our astronauts has been used in the construction industry for over 20 years and has been receiving more attention in recent years as alternate green building methods have been thrust into the spotlight. Radiant barriers work differently than all traditional forms of insulation.
The most commonly used insulation in the past, and is still frequently used today, has been fiberglass batting, loose-fill blown insulation, spray foam insulation and cellulose. It is possible to add a radiant barrier to an existing house and often recommended. All types of insulation are rated with an R-value, unlike radiant barriers. The R-value is how the manufacturers measure thermal resistance, meaning how well the insulation prevents heat from transferring through the insulation.
Radiant barriers are not assigned an R-value, but two different numbers. The first is an emissivity number. The second number refers to the thermal reflective ability of the barrier. The emissivity, or emittance, refers to how much thermal radiation is given off of the material. The emittance rating will be between 0 and 1. As the emittance rating goes up so does the amount of thermal radiation given. Although related, the second rating is the reflectivity of this insulation. The reflectance rating is also given as a value between 0 and 1 or percentage. These figures, when combined should equal 1 or 100%
While the explanation for the emittance and reflectance ratings is somewhat over-simplified, it is important to pay attention to both numbers. The reflectivity rating should be at least.9, or 90%, while the corresponding emittance rating should be low. These numbers need to be disclosed to the home owner by the manufacturer of the barrier.
While it is quite possible to install a radiant barrier in an attic or crawl space, there are a number of differing methods. The two simplest and most cost effective methods are to secure it to the top side of the roof joists, which support the ceiling, or the bottom of the rafters, which form the slope of the roof. There are particulars, though, to which need to be paid attention.
When installing the radiant barrier on top of the joists, possible condensation during the winter months needs to be taken into account. Most barriers will not allow water vapor to pass through. A simple fix is to make sure the barrier is a perforated one which will allow the barrier to breathe while still being able to reflect the heat away from the ceiling and living quarters below. Another alternative is to verify that the radiant barrier being installed has a substrate which will naturally allow any condensation to pass. The challenge of possible condensation does not apply to the installation of the radiant barrier to the bottom of the rafters. Because of soffit vents along the eaves of the roof or ridge vents, air movement should maintain a condensation free environment.
Radiant barriers used as the sole means of insulation may provide decent results; however, when used in conjunction with existing insulation should enhance the monetary savings of any home owner's monthly utility bill. Due to the region where the home is located, results will vary. Local installers should know which method and what type of radiant barrier will be best for each application.
Go to http://www.utilityimprovements.com for further information.
Article independently authored by Daniel Elliott. The content herein may or may not reflect the views and opinions of Utility Improvements.
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