Submitted by Rodney Twyford, NPI Franchise Owner, San Antonio, Texas
The attic of a home is a system of many components working together to help maintain ideal indoor conditions, so the whole attic system should be considered when making energy efficiency improvements. Although I offer some recommended energy-saving tips, this is not in order of largest energy-saving benefits. It is only a practical approach and the recommended order in which to do perform the work.
One of the first places to start saving energy and money in your attic is by sealing up all air leaks, combined with sealing around all walls, doors and windows within the thermal envelope. Most homes in the United States have significant air leaks that if added up typically would be the equivalent of leaving a window open every day, all day long. Air that leaks through your home’s envelope wastes a lot of energy and increases utility costs. Other benefits include reduced noise from outside, less pollen, dust and insects (or pests) entering your home, and better humidity control.
Air sealing an attic can be a challenge and messy for most do-it-yourself homeowners because it typically involves messing with existing attic insulation. However, if you do not feel up to accessing your attic areas, there are a number of qualified contractors who can be hired for this job.
Seal and Insulate Leaky Ducts
Other common energy wasters are air distribution ducts. Research has shown that a high percentage of air distribution systems leak, it’s just a question of how much. Leaky ducts can reduce heating and cooling system efficiency by as much as 20 percent. Sealing and insulating ducts increases efficiency, lowers your energy bills, and reduces pollutants and the impact on the environment through generating the energy to heat your home.
Duct material manufacturers have made considerable improvements over the years to incorporate a radiant barrier, giving ducts the ability to reflect radiant heat. A new air distribution system typically pays for itself through energy savings.
Install the Proper Amount of Insulation
Third on the list of energy-saving tasks is insulation. Most older homes in the United States are underinsulated, and newer homes only have the standard required insulation at best. Most homes can benefit from increased insulation that will pay off year after year and can increase value of the home.
Heating and cooling systems consume 50 percent to 70 percent of a home’s energy. Heat flows naturally from a warmer to a cooler space, so adding insulation helps your home retain heat in cold weather and reject heat in warm seasons, allowing your heating and cooling system to run more efficiently.
Install a Radiant Barrier
One of the last but highly recommended improvements is installing a radiant barrier. Since this technology is not widely known and often misunderstood, I will spend a bit more time on it to explain what it is and how it works.
First, we should know that heat is transferred in three ways: conduction, convection and radiation. It is also important to know that heat does not always rise, as is the common misconception. We know through science, the second law of thermodynamics, that heat naturally wants to flow from warmer to cooler areas, such as from a hot attic to a cooler interior space below.
Radiant barriers are sheets of aluminum foil typically applied to a fiberglass mesh or a Mylar bubble wrap that work to block the transfer of heat from the exterior into the attic and/or interior space, which can reduce the energy efficiency. A radiant barrier works to block heat transfer in two ways: First, the shiny, reflective surface blocks radiant heat by reflecting it, and second, the shiny surface has a very low emissivity to prevent emitting heat through radiation.
The radiant barrier applied to the attic side of roof sheathing, such as Tech Shield, is only a one-sided barrier and works by reducing the emittance of heat from the roof surface through to the attic space. Many of the radiant barriers sold in sheets are double-sided and work both as a reflective barrier and a low-E barrier. The bottom side works the same as the one-sided barrier by reducing the ability to emit heat into attic space, and the top side works to reflect heat radiation away from the attic.
However, in order for both sides to work efficiently, there must be an air space. Without this required air space heat can be transferred through conductivity, thus effectually reducing the barrier’s ability to be a barrier at all.
Some radiant barriers are installed horizontally over insulation across the attic floor. This type of installation could be cause for concern in several ways. First the accumulation of dust eventually will cover and dull the surface, reducing its ability to reflect radiant heat. If this horizontal radiant barrier is double-sided, then the dust can reduce it to becoming effectively a one-sided barrier. So now, as a one-sided barrier, the shiny side facedown on attic floor can still work to prevent heat from emitting into insulation, as long as there is enough of an air space between the radiant barrier and insulation. If the radiant barrier is compressed into the insulation, such as using attic storage, then heat could be transferred through conductivity.
Also, a radiant barrier installed on the floor of the attic directly in contact with insulation could be cause for concern. During winter months, the water vapor in the warm interior air could move upward toward the attic, unless the radiant barrier is highly permeable. This water vapor could condense on the underside of the barrier, causing a reduction in R-value of the existing insulation due to its constant exposure to moisture. Another ill effect of this phenomenon is that the ceiling could rot, cause mold or display wet spots. Moisture can also be generated from bathroom exhaust fans leaking or not properly terminating to the exterior of the house, causing moisture to accumulate within the insulation.
Other disadvantages of installing a radiant barrier on the attic floor is significantly reducing the ability to safely move about through attics to perform maintenance or repair work. Given these known disadvantages, it is recommended in warmer regions to install the double-sided radiant barrier on the underside of the rafters, and taking care not to obstruct proper attic ventilation with the barrier. For best results, it is recommended to ventilate both sides of the double-sided radiant barrier installed across the bottom side of the rafters. This will help carry away the heat between top of the radiant barrier and the roof sheathing, as well as through the attic space.
Finally, a spray-on radiant barrier is a liquid applied to the underside of the roof sheathing, much like paint, and it must be applied at a certain thickness (not watered down). Most spray-on-type radiant barriers recommend the construction to be dust-free (cleaned) and a primer be applied first in order to achieve optimum performance. The advantage of a spray-on-type radiant barrier is the ability to cover more surface area in an existing attic.
However, the disadvantages are making spray-on radiant barriers less popular compared to other products. Although it is easier to install, the main disadvantage compared to foil-type radiant barriers is the higher the emissivity, making it emit more heat through the thermal barrier than that of most foil types. Be sure the label of the liquid product indicates that the emittance is less than .25 as measured by ASTM C1371 — unless the label shows emittance between 0 and .25, they won’t perform as intended. The other disadvantages are that it is only one-sided, it takes additional time and labor to prepare the surface of construction before it is applied, and most of the liquid products are messy — even after they have fully cured, the product will rub off onto hands and clothing.
Tagged: attic, attic inspection, insulation, radiant barrier, Rodney Twyford