What Is Radiant Barrier, Reflective Insulation and IRCCs?
Myths & Misconceptions About Radiant Barriers, Reflective Insulation and Interior Radiation Control Coatings (IRCCs)
RIMA International is dedicated to distributing reliable reflective insulation, radiant barrier or interior radiation control coating product technical information to consumers. This information will help expose exaggerated claims made by those who have misrepresented their performance. We invite readers to view the technical and library pages for comprehensive discussions on technical issues.
Listed below are some of the more common misrepresentations found on the internet and in some literature.
What about claims of exaggerated savings on your energy bill?
Although consumers can expect energy savings after installing radiant barriers in their attics, exact savings are difficult to predict because there are many factors that affect energy consumption. The factors include, but are not limited to, building orientation, occupant lifestyle and climate.
What is the best way to install a radiant barrier? Is it wrong to install a radiant barrier above the roof deck and below the roofing felt?
Radiant barriers must have an air space that faces at least one of its reflective surfaces in order to function properly. When the reflective surface is in contact with another surface, it becomes a direct conductor of heat. Never install a radiant barrier with its low-e surface in complete and direct contact with other materials.
Will dust affect the performance of a radiant barrier in a residential attic?
One method of installing a radiant barrier in an attic is horizontally, directly on top of the mass insulation on the attic floor. This method is most often implemented for ease of installation. Properly installed, this application can offer equivalent performance (i.e. ceiling heat flux reductions) to other installation methods; however, dust accumulation over time will reduce the effectiveness of a radiant barrier installed in this manner.
(Reference: Fairey, P., M. Swami, D. Beal. 1988. “RBS Technology: Task 3 Report.” Florida Solar Energy Center. Publication Number: FSEC-CR-211-88)
What is the R-value of radiant barrier?
This question is often asked and is an indication that there is still some confusion between radiant barriers and reflective insulation. Radiant barriers are always installed with the reflective, low-e (low emittance), surface facing an open air space. Because of a radiant barrier’s low emittance and high reflectance, it can block about 90 – 97% of the radiant heat that strikes the surface, significantly reducing the total heat transfer in and out of a building. However, due to variations in building construction, location and climate – one cannot assign a unique R-value to this application. Calculations can and have been made for very specific applications, but every given application requires its own evaluation.
Will radiant barriers cause roof shingles to deteriorate?
Testing done by the Florida Solar Energy Center has shown that roof shingle temperatures do increase between 5 and 10°F when radiant barriers are installed under the roof deck. The color of asphalt shingles has more of an effect on shingle temperature than the presence of a radiant barrier. No shingle manufacturer limits their warranty when combined with a radiant barrier in the roof system.
Reference: Florida Solar Energy Center
Does reflective insulation really provide an R-10 under a slab, or equal to 2 inches of foam board insulation?
Claims of high R-values for reflective products when they are used as under concrete insulation are not supported by any industry or code body accepted testing methods. Products installed under concrete slabs cannot reflect heat because there are no air spaces present.
(Refer to TB101 – Reflective Insulation Materials Used Under Concrete Slabs.)
Will doubling the product double the benefit?
This entirely depends upon the method of installation. If by doubling up one means just adding a second layer of reflective insulation without increasing the number of airspaces, that is if both layers of insulation are in contact with each other, essentially the only increase in thermal value would be the intrinsic R-value of the added layer. In the case of a double bubble foil product, that would represent about an added R-1. This would not represent an economical insulation option. If, however, doubling up were meant to mean dividing the wall cavity into 3 separate and equal air spaces in place of 2 with only one insulation layer, then the result would be an increase in the R-value.
How can reflective insulation that thin provide much benefit?
The thickness of reflective insulation has much less to do with the overall thermal performance than does the reflective, low-e (low emittance) surface facing the adjoining air space. With respect to reflective insulation materials, the application, including the size of the adjoining air space(s) and direction of the heat flow are the major contributors to the R-value and thermal performance of the insulation system.
Do radiant barriers and reflective insulation only work in hot regions? Are they suitable for use in cold climates as well?
Reflective insulation products excel in hot climates and often are the first choice for insulation in those regions. However, they also provide significant benefits in cold climates where they are used alone and/or when used in combination with other insulation materials in specific applications.
Interior Radiation Control Coatings (IRCCs)
Are ceramic paints as effective as radiant barriers and IRCCs?
One of the major misconceptions in the insulating paint field is that “ceramic paints” can be used on the interior like an IRCC to reduce attic temperatures and lower cooling energy costs. However, the application of a “ceramic paint” to the underside of roof sheathing may increase the attic temperature because “ceramic paints” typically have a higher emittance than the sheathing deck. If a paint does not conform to ASTM C 1321, “Standard Practice for Installation and Use of Interior Radiation Control Coating Systems in Building Systems”, it should not be considered for interior applications in the attic.
(Refer to the Coatings Study under “Technical Info”.)