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Is Radiant Barrier Effective? The Research-Based Facts


does radiant foil really work?

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When building my new home I researched options for making the structure as energy efficient as possible. At the same time, I needed to work within a budget. I considered foam insulation but it wasn’t the right choice for me at the time. I decided to focus on air sealing, blown in insulation, and some form of radiant barrier.

Is radiant barrier worth it? Radiant barrier has been shown to decrease ceiling heat gains by up to 42% in certain tests. This can result in energy savings in cooling costs up to 10%. Multiple studies have confirmed that a radiant barrier is a worthy addition to a home’s thermal envelope.

In the right situation, a radiant barrier system is a cost-effective solution to reducing attic heat and, consequently, energy costs. The key to its effectiveness is in its ability to reduce the transfer of radiant heat.

I’m going to share everything that I have learned in my research. This article will explore the claims, myths, and concerns that are commonly heard. I’ll also share academic and scientific research findings that I reviewed surrounding radiant barrier and it’s effectiveness in reducing attic heat. I have included commercial information from manufacturers only when it helps to demonstrate a fact or perception about the technology.

My goal is to save you the countless hours of research that I endured and provide all of the factual information in a single location. Ultimately, I’ll share with you why I chose to install radiant barrier in my attic, the type of radiant barrier I chose, and the results that I’ve seen thus far.


What is Radiant Barrier?

It’s important to understand what this technology is and it’s designed intent. I spent a great deal of time studying it while planning the building of my new home and this is what I found.

What is a radiant barrier? Radiant barrier is a reflective surface that is designed to provide a boundary against radiant heat between your conditioned air space and the sun. Traditional insulation blocks convection and conduction. A radiant barrier blocks the third type of heat transfer: radiant heat.

Considering the large square footage of attic space in the average house and a roof’s exposure to direct sunlight, an attic is a significant source of heat transfer into the conditioned space of a home (source).

By installing a radiant barrier on the underside of your roof, it is meant to reduce the heat gain in the attic which in turn reduces heat in the living space of your home.

This home efficiency option is available in several forms. There are radiant barrier paints, foil backed OSB or plywood (I’ll refer to these collectively as foil backed sheathing throughout this article), and fail that comes in rolls and can be installed as free-hanging barriers on the underside of your roofing from inside the attic. You can also purchase

Each offers its advantages and challenges which we will explore in the next section.

There are three types of heat transfer; convection, conduction, and radiation. Traditional insulation does a decent job with the first two but is not designed to address radiation. In fact, I learned that traditional insulation actually absords and re-emits radiant heat” at up to 90%!

This is where a radiant barrier comes in.

Radiant materials such as a radiant barrier only re-emit around 5% of the radiant heat according to Home Energy Magazine. So, if you can establish a barrier between the roof and the conditioned space to reduce that radiant heat, you stand to make significant gains, in theory at least.

And to some extent, it stands to reason. Consider how aluminum foil works. When you remove a casserole from the oven, the pan is too hot to touch with your bare hand. But what about the aluminum foil on top? It may be warm but you can easily touch it. It’s not hot like the glass pan.

This is the concept behind radiant barrier systems. It’s like a layer of aluminum foil between your hot shingles and your cool living room!

This was the first eureka moment for me in understanding the potential for a radiant barrier. It came to me while watching a video from a radiant barrier manufacturer. We’ll view this video later when we discuss the importance of air gaps in radiant barrier effectiveness.

Note: Radiant barrier technology is not new and not without a proven history. Developed and originally utilized by NASA in the 1960s, the science behind radiant barrier technology has been incorporated into homes for decades.

You have likely seen this technology used in thermal foil blankets for camping, professional runners, and emergency kits. The idea of wrapping yourself in alumunum foil to stay warm sounds crazy. Yet, that is essentailly how these thermal foil blankets work?


Types of Radiant Barrier

Let’s have a look at the three primary approaches to establishing a radiant barrier between the sun and your conditioned space.

Types of radiant barrier. There are essentially three types of product marketed as a radiant barrier. Each takes a different approach to reduce radiant heat transfer in a home. These include:

  • Radiant Barrier Paint
  • Foil-Backed Sheathing
  • Radiant Barrier Foil

Each of these approaches offer a different level of effectiveness in blocking heat transfer.

Let’s briefly explore the advantages and disadvantages of each of these.

Radiant Barrier Paint

The primary advantage paints marketed as “radiant barrier” have over the other two options is that it can be quickly and easily applied. Unfortunately, the effectiveness of this approach seems to be its only advantage. As you’ll see below, studies have found this to be the least effective approach to heat transfer prevention and in fact, these paints generally do not even meet the criteria to be classified as a radiant barrier.

Foil Backed Sheathing

Many homes being built today utilize this form of radiant barrier in the attic. Instead of regular sheets of plywood or OSB being applied to the roofing joists, foil back sheathing is used with the foil facing down toward the attic, reducing heat through emissivity (more on that later).

The primary advantage to this approach is that, if you are building a new house, you can simply have the contractors use this instead of regular plywood. Of course the disadvantage is that, if your home is already built, it’s not a feasible option.

Radiant Barrier Foil

The final type of radiant barrier we are looking at is the after-market approach which involves stapling radiant barrier foil to the underside of the roofing joists.

A key advantage to the foil is that it can be installed by the homeowner in an existing attic. I am currently in the process of installing it in mine and have been very pleased with how quickly it goes up once you get started.

The one disadvantage that I’ve come across, at least in my situation, is that it’s difficult to apply to high pitched attics. I was able to quickly and easily staple it up in the area above my bonus room since there was much less clearance between the attic and the ceiling joists. The rest of the house, however, has a pitch that is probably 20 feet or higher.

The solution to this as I’ve learned through my research is to essentially build a “false ceiling” of the foil above your head. One suggestion I found for this is to run a series of thin wire or string across the span of the attic and tape the foil around it with foil tape. This would essentially create a large air gap overhead between the foil false ceiling and the high pitch of the attic roof.

There is an advantage to this approach based on research. A study published in 2012 found a direct correlation between an increased air gap and heat transfer. The study noted, “thickness of the air gap has a significant effect on heat gain or loss” estimating that an air gap of around 2 inches can result in a 26% reduction in attic temperatures.

A larger air space between the radiant barrier and the attic roof essentially increases the effectiveness of the radiant barrier’s efforts at reducing heat transfer.

Watch this YouTube video for an excellent explanation of the importance of an air gap. This video will also help you to understand the concepts of convection, conduction, and radiation as heat transfer methods as well as emissivity and reflectivity.

Note: Manufacturer’s video – included to provide visual representation of this principle.

Radiant Barrier Foil Insulation - Why Is Air Gap or Space Required?

Which Type of Radiant Barrier is Best?

A control study was published in 2013 showing the radiant barrier effectiveness of paint, foil backed sheathing, and foil that was stapled onto the rafters. The results were very telling.

Radiant barrier paint performed the worse, providing a heat decrease in the conditioned space of around 19%. Foil-backed sheathing came in 2nd with just under 33% heat reduction.

The most effective radiant barrier solution based on this study was radiant barrier foil stapled to the rafters. This approach resulted in almost 50% reduction in heat transfer to the conditioned space! You can read the full study where these results were outlined at this link.

An important note about radiant barrier paint. Although certain paint-on products are promoted as radiant barriers, the American Society of Testing and Materials International denies that these products meet the reflective criteria to qualify as true radiant barriers.

Rather, they fall into a category known as interior Radiation Control Coatings. This is essentially a lower qualification and though it does promise to provide at least some reduction of heat transfer, it is not on par with true radiant barrier offerings like foil backed sheathing and radiant barrier foil that is stapled to the roof joists.

The Reflective Insulation Manufacturer’s Association International (RIMA) has a comprehensive explanation of this study and key distinctions which you can read here.

In the end, this all has to do with a material’s ability to reflect radiant heat and the stapled up foil approach is the clear winner.

But why?

It has to do in part with a distinction in how the different barriers strive to block radiant heat.

Essentially, there are two ways that a radiant barrier can reduce heat transfer: emissivity and reflectivity.

Foil backed sheathing is an emissivity barrier. Stapled up that has an air space between the foil and the roof provides heat transfer reduction through reflectivity.

This YouTube video explains the concepts very well showing the advantage of reflectivity over emissivity. Note: this is a manufacturer’s product video but the explaination warrants sharing this.

Radiant Barrier Department Of Energy Lab Test Results - (Understanding Reflectivity vs Emissivity)

Does Radiant Barrier Cause Mold?

I must admit, I had this concern when I first began exploring the idea of a stapled up radiant barrier. By creating a closed air space between the roof and the bottom of the ceiling joists, I was afraid that I would be creating a dark, warm, and moist area when mold could grow.

There are a couple of misconceptions in this thinking though, as I learned.

First, you aren’t really closing off anything. If installed correctly, air can and will freely flow from the opening at the bottom near the soffits to the top where it can exhaust out a ridge vent or other venting system.

Second, the type of radiant barrier that I purchased is perforated. It has thousands of very small air holes throughout that facilitates airflow.

The point is, it is not designed in a way that it would be prone to mold growth. This holds true for the foil-backed sheathing as well. It is not intended, nor should it be used, to restrict the natural intake and exhaust of air in your attic’s ventilation system.

Now, it’s worth noting that I’m referring to the stapled up approach. There is another installation option which may be more appropriate if you live in a cold climate.

It involves laying the radiant barrier foil on top of the insulation blanket of your attic. In this case, the Oak Ridge National Laboratory does warn of the potential to essentially trap moisture and condensation in the insulation. The organization cites the importance of proper ventilation to avoid issues. The use of a perforated foil would likely also be wise.


Is Radiant Barrier Flammable?

When I first began researching this I wondered whether or not a radiant barrier product is flammable. If you have wondered this too, then please read this.

Is radiant barrier flammable? A radiant barrier is required to meet certain flame spread and smoke ratings in order to meet building codes. Oak Ridge National Laboratory notes these requirements to be a 25 or less “Flame Spread Index” and a 450 or less “Smoke Developed Index”. The radiant barrier manufacturer you choose will be able to confirm whether or not their product meets these criteria. (source page).

If you shop for the product in a local hardware store, check the manufacturer’s label. If you shop online, look at the manufacturer’s website regarding flammability. I looked at several when I was in the market and many of them had this information prominently displayed.


Is Radiant Barrier Better Than Insulation?

This is a question that I’ve had asked of me a lot since I began the install process at my house.

It’s important not to think of radiant barrier as a replacement for insulation but rather the missing component to a comprehensive thermal envelope solution. Combining a radiant barrier with traditional attic insulation gives you a way to insulate your home from all three types of heat transfer; convection, conduction, and radiation.

Is radiant barrier better than insulation? A radiant barrier is designed to increase the effectiveness of your thermal envelope. It is meant to supplement insulation, not replace it. By reducing the amount of radiant heat reaching the insulation in your attic, the insulation remains cooler and is able to keep your home more comfortable.

Here is an excellent video demonstration from YouTube that clearly shows how a radiant barrier is intended to supplement your existing insulation.

Note: This is a commercial website but the demonstration is worthy of inclusion here as it vividly shows the potential of a radiant barrier solution.

Radiant Barrier Foil Insulation, Go Green Radiant Barrier by HeatBlockers Houston

Will Radiant Barrier Damage My Shingles?

This is a valid concern based on the concept of what a radiant barrier is designed to do. It is essentially intended to reflect radiant heat away from the attic. Since it is installed under the roof, it is reasonable to conclude that additional heat buildup will result in the shingles and possibly cause damage. To find out the facts, however, we need to look at the research.

Does a radiant barrier cause roof damage? According to the Florida Solar Energy Center, shingles only heat up by an additional 2 to 7 degrees compared to shingles that are not over a radiant barrier. This depends to some degree on the color and type of roofing shingles installed. (source).

Although the variance in heat buildup with a radiant barrier is minor, it is worth noting and understanding the difference in roofing color as it relates to attic temperatures.

Darker color roofs absorb light more readily than light colors. The darker your roof, the more light is absorbed and the hotter the roof will be. The lighter and more reflective a rooftop is, the cooler the roof which means less heat is radiating into the attic. (source: Department of Energy).

My point to this is not that you need to go out and buy new roofing material that reflects heat. The point is that if you have a darker roof as many of us do then you will likely benefit from a radiant barrier even more!


Effect on Attic Temperatures

In the south we often install attic ductwork and even central air units in the attic. This is a counter-intuitive building approach since the attic is the hottest (or coldest) covered area in a house yet we try to run warm or cold air through the ducting to keep a house comfortable.

So I wondered if I would be able to reduce ambient temperatures to a point where the attic was not such a hostile environment for my ductwork.

Does a radiant barrier reduce attic temperatures? When installed correctly, a radiant barrier can provide a “notable difference” in attic and insulation temperatures, especially in the summertime and in warmer climates. Reduced temperature of insulation results in less heat transfer into the conditioned space of the home (source).

The study found that the greatest benefit to attic temperatures would be experienced in the south as well as the southeastern regions of the U.S. As a result, these areas would also be the most likely to realize the highest benefit in energy savings.

Oak Ridge National Laboratories also noted that radiant barrier applications stand to reduce the difference between attic temperatures and the conditioned air carried by ducting systems in an attic. They theorize that this reduction in temperature differences would result in more efficient cooling as the HVAC system would be able to deliver conditioned air at closer to its intended temperature (source).

Does Radiant Barrier Work In Winter or Cold Climates?

If you live in a colder climate, you may wonder if there is any benefit to installing a radiant barrier in your attic. I was surprised to learn that there are in fact energy saving benefits for northern states.

Does a radiant barrier work in winter? A radiant barrier can reduce energy loads by up to 10% in winter based on independent studies. By reducing heat transfer from the living space into an unconditioned attic, a properly installed radaint barrier can complement the energy-saving efforts of traditional insulation.

I ran across multiple studies during my research that found deductions in heat transfer from the conditioned space, especially when the radiant barrier was layed across the attic floor over the insulation instead of being stapled to the rafters. To avoid condensation issues, a perforated radiant barrier may be the best choice for this application.

The Office of Scientific and Technical Information found heat loss was reduced by 6-8% in their study (source). Another study, focusing on thermal performance and using a climate simulation process found the reduction in heat transfer to be closer to 10% depending on the material and installation approach used (source).

This YouTube video was posted by a gentlemen in New England. He gives his first-hand experience of the benefits that he has seen from radiant barrier installed on the attic floor in a cold climate.

Radiant barrier for cold attic spaces

Does Dust Reduce The Effects Of A Radiant Barrier?

There is evidence that supports a theory that if dust settles on a radiant barrier foil it can lose its effectiveness as the reflectivity is reduced (source). However, this study noted that the reduction, if any, was insignificant.

And so it goes…

There seems to be a polarized standpoint on this issue with supporters on each side standing their ground. In fact, these are almost word for word quotes from contractors that I spoke with when building my house.

“It’s a waste of money. It stops working when dust gets on it.”

“It never loses its effectiveness, no matter how much dust gets on it.”

I heard both extremes of this. I researched it extensively and found multiple studies supporting both sides of the argument.

One particular study that was referenced multiple times online in the argument against radiant barrier was this one which noted a decrease in the performance of the radiant barrier when covered in dust.

The problem is, I get the feeling no one has actually read the whole paper. While the tests conducted do in fact confirm a “statistically significant” reduction in effectiveness, the author concedes that it still provides a “large reduction” in heat transfer compared to not having a radiant barrier installed.

The study goes on to summarize that even with dust, a reduction in cooling loads of 7% were still observed when compared to having no radiant barrier at all.

In fact, the study specifically concludes that radiant barriers covered in dust continue to be effective in reducing attic heat transfers and house cooling loads.

And that is the part of the study that keeps getting left out.

And so, back to the original question…

Does Radiant Barrier lose its effectiveness as dust collects on it? Like every other part of your home, the efficiency of a radiant barrier may degrade somewhat over time. Yet even with that degradation, it provides more efficiency than not having it.

The effectiveness of your insulation, shingles, and even your slab may degrade some over time too, but I would still recommend having them.


Conclusion

Scientific variables aside, research has proven that the inclusion of a radiant barrier provides additional heat transfer reduction in a comprehensive thermal envelope.

It is not meant to be a replacement for fiberglass or cellulose insulation. It is intended to complement those traditional insulation methods by reducing the amount of radiant heat transferred to your conditioned living space.

radiant barrier

As this report has shown, the impact of a radiant barrier on your energy bills will dependant on several factors including the type of radiant barrier used, installation method, and climate.

But regardless of the percentage of savings that any particular installation may experience, there is one commonality throughout all of the studies that we need to take away from this:

Every independent study demonstrated some level of heat transfer reduction when a radiant barrier was installed.

We can argue over the percentage of heat reduction and tests varied depending on the installation method and climate, but none of the studies reviewed demonstrated either no heat transfer reduction or an increase in heat transfer reduction. The bottom line: a radiant barrier is a viable addition to your thermal envelope.

Which Radiant Barrier Brand Should You Use?

In our next post in this series, I’ll be performing side-by-side tests of several brands of radiant barrier foil. We will test each sample for durability, flammability, and even perform a thermal imaging test to validate heat transfer reduction.

Stay tuned!

Paul

As a homeowner, I am constantly experimenting with making the structure of my house more energy-efficient, eliminating pests, and taking on DIY home improvement projects. Over the past two decades, my family has rehabbed houses and contracted new home builds and I've learned a lot along the way. I share my hard-learned lessons so that you can save time and money by not repeating my mistakes.

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