Josh Lowe's Dr. Energy Saver Blog

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What Is an R-Value?

What Is an R-Value?

Every industry seems to have its own jargon, and construction/insulation is no exception.

When you look up the definition of R-value, you will see some garble like “the capacity of an insulating material to resist heat flow.” Or you might find the equally mystic “R-values measure the thermal resistance per unit of a barrier's exposed area.”

If you look on the “Talk Like a Pirate Day” site, then it’s “Arrrrrrr Value!”

We don’t have to completely understand about transfer of heat and that First Law of Thermodynamics. The most important part to know is the higher the R-value, the better. Insulating materials keep heat from moving from one area to another area that has a different temperature.

Ever open a door to the outside on a really hot day and feel hot air blast over you? The space between you and the outside has a really LOW R-value. It wasn’t able to keep the heat from moving.

The movement of air in, out, and through your home can affect how well the insulation in your home actually insulates (meaning, reduces the heat movement). When air moves, it carries with it many things, such as heat. The stronger/faster the air movement, the faster the heat moves through insulation.

Different types of materials have different R-values for the same thickness. And you only have so much room in an attic, a wall, or in the crawl space. For example, to achieve the recommended R-value of R-60 in an attic, fiberglass takes 22 inches in height, yet blown in cellulose only needs 16.5 inches in height. Closed-cell spray foam takes up even less space.

Fiberglass used to be the main insulating material. Many of us have a few inches of it in our attics or stuffed under the floor in our crawl space. You’re probably now thinking, “Hey, that’s not enough to do much good!” See, no need to know about thermodynamics. Five inches of fiberglass in your attic only gives you about an R-11 value (before the fiberglass absorbed moisture and collapsed down, as it tends to do). No wonder you are cold in your own home.

Current recommended building codes in our area is R-38 in the attic. This is moving to R-49; R-60 is optimal and recommended under Energy Star standards.

When deciding how to make your home a more comfortable place to live in, just adding in some insulation usually is not an effective, long-term solution. The first thing you can do to ensure the R-value you are now looking for is met—seal the holes in your attic and your crawl space.

Then, choose a better insulating material for the volume, such as blown-in cellulose or closed-cell spray foam. These are more effective and longer-lasting materials than outdated fiberglass.

For more information, the Building Performance Institute has a great article on R-value at http://www.bpihomeowner.org/blog/bpi-phrase-month-r-value

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