Why does radiant barrier work

Those items then continue to build up and radiate their own heat in all directions. While half of that heat may go back outside, the other half continues right on into the attic space. This heats up the insulation in the attic, the floor, the drywall that makes up your ceiling, and eventually, penetrates into the living space. Remember how it heats up everything in the attic? That includes all of the AC ductwork that carries cool air throughout your home. Seems counterproductive, right?

Radiant barrier is the first step to block radiant heat coming in from the sun. Your attic floor insulation is the second step which blocks conductive heat flow to the rooms below.

Radiant barrier products actually make your attic insulation work better. It even works in other applications as we recently installed radiant barrier in a shop. Other technologies exist to help save energy as well. Bosch geothermal heating and cooling systems make a great example. Insulation is great. Here are some typical recommended home insulation R—values for wood-framed buildings per Energy Star:. First, insulation does nothing to defend against rising radiant heat levels in the attic. It will eventually heat up as nothing blocks that transfer of heat.

Second, insulation is made better by a radiant barrier. If the insulation in your attic stays cooler, your living space stays cooler. That means lower energy bills and faster cooling. You can save money over the long haul, enjoy better cooling in warmer climates, and solve problems related to achieving cooler temperatures in your home. When he's not remodeling part of his house or playing with the latest power tool, Clint enjoys life as a husband, father, and avid reader.

A radiant barrier's effectiveness depends on proper installation, so it's best to use a certified installer. The reflective insulation trade association also offers installation tips. It's easier to incorporate radiant barriers into a new home, but you can also install them in an existing home, especially if it has an open attic.

In a new house, an installer typically drapes a rolled-foil radiant barrier foil-face down between the roof rafters to minimize dust accumulation on the reflective faces double-faced radiant barriers are available.

This is generally done just before the roof sheathing goes on, but can be done afterwards from inside the attic by stapling the material to the bottom of the rafters.

When installing a foil-type barrier, it's important to allow the material to "droop" between the attachment points to make at least a 1. Foil-faced plywood or oriented strand board sheathing is also available. Note that reflective foil will conduct electricity, so workers and homeowners must avoid making contact with bare electrical wiring.

If installed on top of attic floor insulation, the foil will be susceptible to dust accumulation and may trap moisture in fiber insulation, so it is strongly recommended that you NOT apply radiant barriers directly on top of the attic floor insulation. Subscribe to receive updates from Energy Saver, including new blogs, updated content, and seasonal energy saving tips for consumers and homeowners.

One practical example of a radiant barrier that makes sense in both hot and cold climates is when a metal roof is installed on strapping, which is installed on top of foil-faced polyiso rigid insulation or on top of a radiant barrier placed over a different type of insulation such as XPS or stone wool.

In either case, you can actually reduce the heat transfer from the roofing to the insulation during the day and heat transfer from the insulation to the roofing at night by minimizing the radiative heat transfer across the airspace.

A radiant barrier works in walls, too. With a ventilated airspace behind the cladding, as in a rainscreen, if the next layer on the other side of that airspace is a radiant barrier, it could reduce the heat flow. Perforated radiant barrier material is available, but it can still be vapor impermeable enough to cause condensation. How much you reduce heat flow across the enclosure with a radiant barrier depends on how large the temperature differences are.

Finally, remember that a radiant barrier only works when it is clean and shiny, which preserves its reflectivity. If it gets dirty or dusty during construction or during operation, it stops working as a radiant barrier and works more like a typical surface. I'm curious what your comments are with regard to the product called Energy shield that is based on NASA technology. And one must always remember that there must be an assembly and an air gap on at least one side. In the 's there was a 5 layer reflective barrier designed to fit into wall cavities.

This actually was better than mass insulation, but fiberglass manufacturers had more money and easier installation in some situations. They took the market. Remember that it is about an assembly and or installation for purpose, not about the material being insulation in itself.

Never listen to those that say there is no R value to the material, remember that the R value for barrier is always as an assembly and as installed for purpose actually mass insulation's total effectiveness is also as an assembly.

In areas of attics that have knee walls that are walls to the interior, use the maximum mass insulation then staple thermal barrier OVER that insulation as well, this helps slow convection as well as stop radiant heat both directions from house and to house. Under the rafters, or under the roof deck and under the rafters is the FIRST and foremost installation in tropical to hot summer climates to stop thermal radiation into the attic.

Where winter temperatures are COLD on top of mass insulation stops thermal radiation from leaving the insulation! In instances where an enclosed space unvented can be made, especially with thermal barrier and a gap and thermal barrier again it can be VERY effective in radiant heat transmission in both directions.

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. 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. This is the concept behind radiant barrier systems. 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.

Note: Radiant barrier technology is not new and not without a proven history. Developed and originally utilized by NASA in the s, 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. 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:. Each of these approaches offer a different level of effectiveness in blocking heat transfer. Unfortunately, the effectiveness of this approach seems to be its only advantage.

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. 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.

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.

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 found a direct correlation between an increased air gap and 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. A control study was published in showing the radiant barrier effectiveness of paint, foil backed sheathing, and foil that was stapled onto the rafters.