What is a Radiant Barrier and How Do They Work?
Did you know that the same technology that NASA uses to insulate space stations can make your home more comfortable during the hottest summer months and save you money. Radiant barriers look straight out of science fiction, highly reflective panels that literally bounce heat back to where it came from, but the results are undeniable.
This article will look at the history of the radiant barriers, the physics behind how they work, and what sort of benefits you can expect from adding one to your home.
What exactly is radiant barrier insulation?
Radiant barrier insulation is a type of insulation which works by reflecting heat away from your living space. Unlike traditional insulation which slows the transfer of heat via convection (air flow) and conduction (physical contact), radiant barriers block heat flow via radiant energy.
History of radiant barrier insulation
Radiant barriers are often thought of as a modern invention, with NASA usually getting the credit for popularizing their use. While it is true that radiant barrier foil was pioneered by NASA to protect their space-going vessels, the potential of reflective insulation was recognized long ago.
In the 1800s the French physicist Jean Claude Eugène Péclet discovered that mirror-coated steel plates could be arranged in such a way to provide as much insulation as 3” of cork. At the time the discovery was of limited utility as mirrored surfaces were heavy, rigid, and expensive, but the underlying theoretical principles were established long ago.
Theory gave way to practice when NASA developed a method of applying a uniform reflective coating of aluminum to a lightweight, flexible plastic substrate. This reflective material was used to provide thermal insulation for nearly all NASA missions since the 1970s and has been used on everything from spacesuits to the James Webb Space Telescope.
What are radiant barriers made of?
Radiant barriers are thin, flexible sheets of plastic (usually a type of PET, the same type of plastic as water bottles) coated with a microscopically thin layer of aluminum foil. For ease of handling, sometimes these sheets are affixed to a substrate material like cardboard or plywood, creating a rigid panel with a reflective surface.
Radiant barriers can be one-sided or two-sided. Single-sided radiant barriers only have a reflective surface on one side, and thus only protect against heat transfer in one direction. Two sided radiant barriers are reflective on both sides and prevent heat flow from both above and below.
How does a radiant barrier keep my house cooler?
In order to understand how radiant barriers work, there are a few definitions to know first:
Emissivity: the amount of energy a material gives off as thermal radiation when heated. This number is always given as a number between 0 and 1, with higher numbers indicating more heat being given off.
Reflectivity: this describes the amount of thermal radiation that an object reflects. Like emissivity, this number is between 0 and 1, with higher numbers indicating more reflectivity. For opaque objects, the sum of emissivity and reflectivity will always be 1.
Radiant barriers work by having a high reflectivity (typically .9 or greater) and thus a correspondingly low emissivity. A reflectivity of .9 means that 90% of the radiant heat arriving on the barrier’s surface is reflected away, with only 10% being absorbed and re-radiated below it.
Since radiant barriers rely on their reflectivity, dust accumulation and corrosion can reduce their effectiveness. This makes it important to choose a high quality barrier and install it in such a way to limit dust build-up.
When installed in your attic, a radiant barrier works by reflecting the radiant energy coming off of the inside of your roof, up and away from your living space. To a lesser extent, a double sided radiant barrier can help keep heat inside your home in the winter, although this effect isn’t as pronounced.
If you are installing a single-sided radiant barrier, you will want to have the reflective side facing up towards your roof. These barriers must face an open air space to work, as they only reflect radiant heat and do nothing to help for conductive heat, or the transfer of heat through an object.
How are radiant barriers installed?
In attics, there are two common types of radiant barrier installation: attic floor installations and stapled installations.
Stapled Installations
In stapled installations the radiant barrier material is directly affixed to the underside of your roof. Depending on the style of your roof’s construction (truss framing versus conventional framing) the exact details of the installation may vary, but the effect is the same.
Your entire attic will benefit from the cooling effects of the radiant barrier insulation, the insulation will be protected from dust build-up, and your storage space will be unaffected. This is our preferred method of installation as we believe it provides homeowners with the best results.
Attic Floor Installation
Attic floor installations are exactly what they sound like, the radiant barrier materials are laid atop the floor of your attic. This type of installation is the easiest, but may result in greater heat gain in your ductwork, is more susceptible to dust accumulation, and takes away the ability for you to use your attic space as storage.
Is a radiant barrier a substitute for traditional fiberglass insulation?
Radiant barriers are great at reducing your cooling costs in the summer, but are ultimately not sufficient when used by themselves. Traditional insulation works by preventing heat transfer via conduction and convection, effectively isolating the interior of your home from the outside. A radiant barrier may help your home heat up more slowly, but will do little by itself to keep your air-conditioned home cool.
There are applications, like carports, where radiant barriers are actually superior to insulation. An insulated roof of an open-air carport will do little for the temperature below it, while a radiant barrier will result in far less heat being projected from the carport’s ceiling.
Does a radiant barrier help keep my home warmer in the winter?
While theoretically a double-sided radiant barrier can help keep your home warmer in the winter, in practice the benefits appear to be quite slim. Your best bet for keeping your home comfortable and utility bills low in the winter months is to ensure that your attic insulation meets the minimum recommended r-value for your region.
South Carolina building code requires an r-value of 30 in attics, and r-38 is recommended. If your attic is underinsulated, adding more fiberglass insulation at the same time as installing a radiant barrier is a great way to boost your home’s energy efficiency year round.
Is getting a radiant barrier installed in my attic worth it?
In hot climates, radiant barriers are almost always worth it.
Your precise energy savings will vary depending on a variety of factors (such as whether or not you have ductwork in your attic, how well the ductwork is insulated, the type of radiant barrier material you choose, and more) but most households will see up to a 16% reduction in cooling costs. As energy costs go up (and unfortunately they are trending that way), your savings will also go up.
One of the biggest advantages of a radiant barrier is improved indoor comfort. Since less heat will make it into your home, your home will stay at a more consistent temperature instead of swinging from “too hot” to “too cold” as your air conditioning cycles on and off. An added benefit to this enhanced comfort is reduced strain on your HVAC system will allow it to last longer.
Ultimately, between lower energy bills, increased comfort, and a longer life for your HVAC system, adding a radiant barrier is an easy choice for anyone living in the south!
Ready to Add NASA-Tested Energy Efficiency to Your Attic?
If you’re looking for ways to stay comfortable and save money in the summer, adding a radiant barrier to your attic is a fantastic addition to traditional insulation. By blocking radiant heat transfer your HVAC system will need to do less work, lowering your utility bills and making your home a more pleasant place to be!
If you’re ready to add space-age technology to your attic then contact Dragon Vapor Barriers and Insulation for a free quote!