It’s a fact - heat rises which means the second story of our homes is much harder to keep cool in the summer.  Between heat rising and the sun’s radiant energy entering our homes the temperatures in our attics can reach as high as 150 degrees!  This is good news for Netflix; they get paid whether I sweat through a movie upstairs or not.  The news is not as good for the rest of us as our utility bills go up just as the comfortable space upstairs seems to melt away in the summer heat.  All of this has left me wondering, is installing a radiant barrier in my home actually worth it?

A quick introduction to heat transfer:

Heat travels in a combination of three ways; conduction (from a hotter to a colder material via touch), convection (when a liquid or gas is heated, becomes less dense, and rises) and more importantly for this discussion, radiation- where heat travels in a straight line away from a hot surface and heats anything solid as the wave of energy hits it.  Simply put, when the sun heats a roof, the sun's radiant energy is the driving force that makes the roof hot which in turn makes the attic hot. 

So, what is a radiant barrier?

According to the U.S. Department of energy a radiant barrier consists of a highly reflective material that reflects radiant heat rather than absorbing it. These barriers are installed in homes—most commonly in attics—to reduce summer heat gain and winter heat loss.  The Reflective Insulation Manufacturers Association (RIMA) takes this definition further by distinguishing between radiant barriers and reflective insulation based on whether the air space around the material is open or enclosed:

·        Radiant Barrier – specifies that the reflective material face an open air space.

·        Reflective Insulation - reflective material like aluminum foil which act as low emittance surfaces (low radiation of infra-red energy) that are bound to oneor more enclosed air spaces.  Besides emittance, reflective insulation differs from conventional mass insulation because it does not have significant mass in which to absorb and retain heat.

Types of Radiant Barriers

Radiant barriers are most often composed of aluminum that is applied to one or both sides of a number of materials including; foil, paint coatings, metal roof shingles, laminated roof sheathing, and even reflective chips, which can be mixed with loose-fill insulation. Substrate materials include kraft paper, plastic films, cardboard, plywood sheathing, and air infiltration barrier material.

Exactly how do they work?

A radiant barrier's goal is to reflect radiant energy away from your home.  A barrier’s performance is determined by three factors:

• Emittance – the ability of a surface to emit radiant energy. It's expressed as a number a between 0 and 1. The lower the value, the lower the emitted radiation.
• Reflectivity – a measure of how much radiant heat is reflected by a material. It's also expressed as a number between 0 and 1.  The higher the value, the greater the reflectivity.
• The angle the heat wave strikes the surface—a right angle (perpendicular) usually works best.

All radiant barriers must have a low emittance (0.1 or less) and high reflectance (0.9 or more). Of these factors, the angle the heat wave strikes the surface has the most influence on how well any shiny surface acts as a thermal insulator. When it comes to these properties, there is little difference from one brand of radiant barrier to another.  Most products have emissivities of 0.03–0.05, which is the same as a reflectivity near 97%.

What is best for Southlake homes?

Radiant barriers are more effective in hot climates than in cool climates. There is little argument that radiant barriers can lower cooling costs when used in a warm, sunny climate like those in Texas. The reduced heat gain may even allow for a smaller air conditioning systems. But in cool climates, it's usually more cost effective to install more than the minimum recommended level of insulation rather than a radiant barrier.

In order to maintain competitive selling prices, homes today are regularly are built with less than the ideal amount of insulation.  Furthermore, the older the home the less likely it is to have adequate attic insulation.  Additional attic insulation in conjunction with the installation of a radiant barrier can be a winning proposition for your home’s heating and cooling.

OK…you’ve got my attention, but when it comes to spray-on versus foil applications… which should I choose?

If its energy efficiency and cost savings on your utility bills that you are looking for, then it should be noted, making the choice to install a radiant barrier, regardless of the material is a definite step in the right direction. 

Spray on radiant products (also know as Interior Radiant Control Coatings or IRCC) are low emittance, paint-like materials which reflect radiant heat.  If installed correctly they can have advantages over previous types of radiant barriers (foils) including better coverage and longer lifespan.  It can be sprayed over nail punctures in a uniform manner, so there are no holes or gaps in the barrier. 

Both radiant barriers and IRCCs can contribute to the overall thermal performance of a building. Just be sure to do your homework before purchasing a low-emittance paint product. If it's being called “radiant barrier paint," make sure to review the emittance levels, ask for test data and make sure it meets the American Society of Testing and Materials (ASTM) standards before you buy.

Roger Zedicher of locally owned AAA Heat Stop exclusively installs foil-based radiant barriers and says, “Foil products block up to 97% of all radiant heat which is much greater than spray on products.  Lee Austin, co-owner of American Radiant Barrier, another locally owned installer, says, “Spray on products at best block only 70-75% of radiant heat.”  Both also agree, foils provide a much greater energy savings in winter months than spray-on products.”

What about the installation process?

Spray on radiant barriers are applied, like a latex paint, directly onto the underside of the roof.  Also, like a latex paint there is a minor odor that is barely noticeable and dissipates within a few hours.  One even coat of spray is sufficient and a reputable installer should tell you, a second coat will not provide any additional effectiveness.

There are two ways to apply a foil radiant barrier; the first method is to “Staple Up” the foil directly to the underside of the roof’s rafters thus blocking the radiant heat from coming into your attic. The second and preferred method for AAA Heat Stop is to “Lay Down” the foil directly on top of your attic’s insulation and stapling it to the vertical insulated walls in the attic. This particular method provides a greater level of radiant heat resupply within your home’s living space during the winter and provides full year round savings.

How much should we expect to spend on a quality radiant barrier?

Spray-on radiant barriers usually start in pricing around $0.60 per sq ft.  Where foil based applications begin at $0.70 per sq ft. for “Lay Down” and $0.90 per sq ft for the more labor intensive “Staple Up” application.  So, beginning ranges for an average Southlake home of around 5,000 sq ft. one should expect to estimates to start anywhere from $3,000 and up for sprays and $3,500 to $4,500 and up depending on which foil application you choose.  These estimates are only for the barriers themselves.  Additional costs may result from upgradingyour insulation and ventilation systems which are also important to maximize radiant barrier systems.

What is the return on this investment?

According to AAA Heat Stop’s Zedicher, “a properly installed foil radiant barrier will save you money in many ways from reduced energy costs, heat damage to your attic and wear and tear on your heating and cooling units.  A foil radiant barrier system can save as much as 25% off of your annual heating and cooling bills.  Depending on the size of your home a foil radiant barrier can pay for itself within three to six years.  The larger your home is, the greater the cost benefits, which can lead to an even quicker return on your investment.

With a lower quality barrier to radiant heat, spray on barriers although less expensive to install will most likely require a longer period to actually see a return on the investment.

Foil applications may cost a little bit more than the average spray but the additional investment does produce a better cost savings result over time.