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How Radiant Barrier Works in Attics

What it is and how it works

What is radiant barrier?

Radiant barriers (also known as reflective insulation) are a type of thermal (heat) insulations that inhibits heat transfer by thermal radiation (or heat by non-contact, i.e. across air).

How does it work?

Infrared, or radiant heat, is invisible. Think of a mirror; if you hold it up to the sun, you can reflect the light on your arm. You see the light, but you feel the radiant heat. At night when the sun goes down, your home is instantly easier to keep cool, right? Why? Because when the sun went down the radiant heat gain on the home was reduced. So even though the air temperature may only drop a couple of degrees, there is a big difference is how the surfaces feel.

Does radiant barrier keep my house warmer in winter too?

Radiant barrier also improves the R-value of your insulation by reducing convective looping so your home stays warmer during the cold seasons. Watch the video below to find out more.

Does it promise dramatic results? How much will I save?

What makes radiant barrier foil so effective in reducing energy bills in the summer? Radiant barriers work by blocking radiant heat from being absorbed into our homes, garages, barns, etc. resulting in a more comfortable and energy efficient space. In essence, radiant barrier is like shade and when installed in your attic (or anywhere else where you have a radiant heat source) it reflects that heat away from the area you’re trying to cool.

You probably already have some form of radiant barrier at work in your home. For example, do you have the shiny silver flex ducts in your attic? These are insulated tubes with a radiant barrier covering. The radiant barrier reduces heat from entering the duct work and effectively makes the R-Value of the insulation greater. Conceptually, this is what we are trying to achieve for your whole attic.

In theory if all of our homes were under the shade of a tree, we wouldn’t need radiant barriers. Since that is not the case, radiant barrier foil is the next best thing to naturally occurring shade. Simply put: radiant barriers reduce the amount of heat entering the home/building. Reducing the amount of heat gain helps to reduce the energy needed to remove the heat (air conditioning) and makes the living space more comfortable.

How well a radiant barrier works depends on several things. Generally the more roof surface you have, the greater the impact. For example, installing foil insulation on a single story ranch style home will have a greater impact than a stacked two story home with a small attic. Remember, your home is essentially a box with five basic exterior sides. The greater the roof portion (or top side), the greater potential impact overall.

How much electricity would you save if your roof was shaded? This is realistically the most you will save by installing a radiant heat barrier in your attic. Nothing more, probably a little less. On a 90ºF day are you still going to run the air conditioner? Yes, it’s 90°F!
After installing a radiant barrier your air conditioning will run less and more efficiently, but it will still run. However, on a 75ºF day the radiant barrier might just keep you from having to run your A/C at all. Remember, reflective foil insulation is like shade, so the more coverage you have, the better your results.

Generally you can expect a 5 to 25% savings; one story ranch-style homes typically have the highest percentage savings. No matter what the percentage is, the dollar payback remains consistent. On a two story home, you might have only half the savings compared to a single story home but you also probably only installed half the amount of foil and had a lower total installation cost. So no matter your investment, it will match your return.

Are There Different Types of Radiant Barrier?

Yes, but a foil product will work much better than a radiant barrier paint, ceramic paint additive or micro-spheres. Also, sheets of foil are more practical and economical that shredded pieces of aluminum (radiant barrier chips) and more effective because they allow for full coverage and easy access to your attic, if needed. Learn about the differences between Radiant Barrier Paint vs Radiant Barrier Foil.

There are also bubble products with foil attached, foil on foam board and foil attached to fiberglass insulation. None of these products really offers an advantage over just the layer of foil we make & many don’t have a place on the rafters up in the attic. Learn why bubble foil products and radiant barrier with insulation attached aren’t necessary in a standard attic application.

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