Some folks think that if the double the thickness of attic
their attic insulation that it will reduce their heating and cooling bills by
50%. Doubling the R-value of the
insulation in your attic does not cut your home heating bill in half. Here is
why.

**First, what is R & U all about?**

Insulation is
rated by its *resistance* to heat flow
and is measured in units of R-value. The R-value is used in selling insulation
because bigger is better.

It is easier to
sell a product when bigger numbers mean it is worth more. It is harder to sell
stuff to people, when lower is better.

R-value is an accepted
product labeling number to make it easier for folks to understand that thicker
is better. And, worth a higher price.

The inverse of
thermal resistance is conductance, referred to as the U-value. The U-value is
equal to one divided by the R-value (U = 1/R). Your remember fractions and
algebra from school right?

The U value is
important to engineers because it describes how fast energy is traveling in or
out of your house. It is the number we use in our heat loss calculations.

In the English
speaking part of the world, we count U-values in Btu/square
foot-Fahrenheit-hour. You don’t need to remember that. Just hold on to the idea
that it is the speed of escaping energy, so lower is better.

**So how do you use R-value?**

R-value is intuitively
easier to understand, the higher the R-value, the better the insulation.
R-values of different components can be added. As an example if you have three
layers of R 7 insulation in your attic the total R-value = 7 + 7 + 7 = 21

You cannot add U-values
as easily. Watch out here come the fractions and decimals. Total U-value = 1/(7
+ 7 + 7) = 1/21 = 0.048

**Let’s see that visually**

This graph shows the speed of escaping energy on the left. Squint so you can see the decimal point. The highest value is point 3 with zero at the bottom of the graph. The R-value is shown across the bottom of the graph.

Look at the graph
and notice two things.

One. The speed of
escaping energy is slowed a lot for each little bit of insulation until you
reach R 14 where it turns the corner.

Two. From R 28
onward, there is very little improvement.

If you were to
improve attic insulation from R-7 to R-21, for example, you could cut you
energy losses through the ceiling by 65%.

Going from 1/7
versus to 1/21 U-value (or from 0.14 to 0.05) is a 65% improvement.

In most homes
about 35% of the heat is lost out the roof, the rest gets out through the
walls, windows and by air leaks. Therefore, the overall energy bill for the
heating season would be reduced by about 23% (a 65% improvement of 35% of the
heating bill.)

In this example,
three times as much insulation saves less than one quarter of the heating bill.

The myth persists
that, if R-11 insulation in your house saves heat and money, R-22 insulation
saves twice as much. However, the energy and money you save by adding more
insulation diminishes quickly.

Look at the graph
again. Starting with an R-value of 3.5, every doubling of units in R-value cuts
the speed of heat loss through the wall or ceiling by about half. The R-value
points shown on the graph are selected because they are double the previous
number.

As the thickness
(R-value) gets higher, the speed of heat escaping through the ceiling soon
becomes tiny. It reaches a thickness where adding more insulation costs more
than it is worth.

**So what do I recommend?**

If the insulation
in your attic is less than R 30 (9 inches or less of fiberglass) then you
should add more.

Because the
amount of labor to do the job does not change much with thickness, it is best
to do the job once. By that, I mean add as much as you need in one new layer.
Make it thick enough so that you will not have to do it again when the price of
energy goes way up.

You should target
a total of about R-50, plus or minus 10. The number does not need to be exact.
R 60 is good for far North America. R 40 is good where the snow melts between
winter snowfalls. If it hardly ever snows where you live, R 40 insulation will
save on your summertime air conditioning bill.

I recommend going
big and do it just once by adding one new layer of fiberglass. Use the thickest
available single layer of unfaced fiberglass batt insulation that will get you
near R 50. That is about 16 inches of total thickness.

The cost to bring
in and set up the equipment for blown in loose fill insulation is the same no
matter how deep you fill your attic. So, I suggest you shoot for a total of 16
inches deep.

Yes the material
cost for thicker is higher, but by going with one new layer that takes you to a
total of about R 50 you only pay the labor cost once. Or, if you do it yourself
you only risk falling through the ceiling once.

That will give
you plenty of insulation now and still do the job when the price of home
heating fuel goes up.

Click here for a free money saving report written by the Energy Boomer titled HOW SAVE MONEY ON YOUR NEXT HEATING BILL