How to Insulate Your Attic and Save Money Year-round

Adding attic insulation is one of the easiest ways to reduce your energy bills. Here’s how to know whether you need more.
By Megan Hirt
July 17, 2007

Adding insulation to your attic can make your home more comfortable and energy-efficient year-round.
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As summer winds down, probably the last thing on your mind is climbing into your attic and putting up more insulation.

But consider this: A well-insulated attic could slash your air conditioning bills throughout these warmer months in addition to reducing heating costs once winter rolls around.

“Adding additional cellulose insulation to an attic is often one of the most cost-effective strategies for improving the energy performance of a home,” says Alex Wilson, author of Your Green Home and president of BuildingGreen, a company that helps businesses improve the environmental performance of their buildings. “Not only will the added insulation reduce heating and air conditioning bills, but it will also improve comfort by helping to seal air leaks.”

Here are steps to get started on this money-saving project that’s relatively easy to do yourself.

1: Grab a yardstick or tape measure and make the ascent into your attic. Determine the R-value (the resistance to heat flow) of your current insulation by measuring its thickness in inches and multiplying that number by the R-value per inch for your type of insulation:

Fiberglass blanket or batt 3.2
High-density fiberglass blanket or batts 3.8
Loose-fill fiberglass 2.5
Loose-fill rock wool 2.8
Loose-fill cellulose 3.5
Perlite or vermiculite 2.7
Expanded polystyrene board 3.8
Extruded polystyrene board 4.8
Polyisocyanurate board, unfaced 5.9
Polyisocyanurate board, foil-faced 7.0
Spray polyurethane foam 5.9

For example, if you have loose-fill cellulose attic insulation that measures 10 inches thick, you have an R-value of about 35.

2: The amount of insulation you need in your attic depends on the climate of your region. Find your zone on the map in the Image Gallery, then use the chart below to find the R-value recommended by the U.S. Department of Energy (DOE). For more information, check out the DOE’s Insulation Fact Sheet.


Zone  

Heat Source   Recommended R-value  
  Gas   Heat

Pump
 
Fuel

Cell
 
Electric

Furnace
 
 
1  
X
X
X
X
49
2  
X
X
X
X
49
3  
X
X
X
X
49
4  
X
X
X
 
38
4  
X
 
 
X
49
5  
X
X
X
 
38
5  
 
 
 
X
49
6  
X
 
 
 
22
6  
 
X
X
 
38
6  
 
 
 
X
49

 

3: Subtract the R-value of your current insulation from the recommended R-value to find out how much insulation you need to add.

So, continuing the example above, if you live in Zone 2 and heat with gas, subtract 35 (determined in step 1) from the recommended 49, which gives you 14. This means you need an additional R-14 in insulation, or 4 inches of loose-fill cellulose insulation (14 divided by 3.5 equals 4). For a 1,500-square-foot attic, adding an additional 4 inches of loose-fill cellulose insulation would cost about $250. Some home improvements stores offer free rental of an insulation blower with the purchase of a certain amount of insulation.

It’s important to note that you don't have to add the same type of insulation that’s already installed in your attic, so consider choosing a greener insulation option. (You would need to recalculate the amount of additional insulation you need from step 3 using the R-value per inch for your desired type of insulation.)

For information on the different types of insulation, including costs, environmental impact, advantages and disadvantages, check out All About Insulation. For a step-by-step guide to installing your insulation, visit Owens Corning’s attic insulation page.

Have you added insulation to your attic and enjoyed lower energy bills? Share your know-how by posting a comment below.


Megan Hirt is an Associate Editor for MOTHER EARTH NEWS. Find her on .


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Post a comment below.

 

cellulosefacts
7/24/2009 9:46:26 AM
Is there a conspiracy to misstate the R-value of cellulose insulation? Almost all cellulose has a rating of R-3.8 per inch. It's R-3.8 per inch whether it is "loose fill" in attics or packed tightly in walls. If painting your roof actually cools your living area down then you clearly are in need of cellulose insulation in your attic and probably walls too.

Cindy_3
9/24/2008 9:33:53 AM
I have recently had insulation blown into the floor joists in my attic. I am wondering ig it would be a good idea to put batting the between the joists in the roof as well, or would this trap too much heat and moisture? I only have two end gables for vents, not raised roof venting like in the newer homes. Thanks!

ernest simmons
11/23/2007 12:00:00 AM
Just a comment on attic insulation,I have found the cheepest way to insulate.you can go to lowes or home depot and rent a machine(Free) with a deposit of 250.00 to blow in recycled newspaper that it treated not to burn.a bale is about 8.00 and the returne to you home is tremendous.we are in the process of adding 8 more inches for a cost of about $1500-2000 sf in attic.we have a attic space of over 3000 sf floored.we also left a few inches of air(Also a insulator) below floor.in areas where water lines run in attic we used some fiberglass(so as to uncover it without a mess) if we ever need to repair or add a line.we also did this over electrical panels.we have 2x6 roof construction and on the gable end it was suggested to us to use 2" sterform wedged between 2x6's with a one inch air barried between outer covering.this was said to be very effective.then with the 2" foam in the middle of 2x6 it was suggested to add 3- 1/2 glass or paper insulation.we beleive the r-factor will be greater useing this method.check it out.have a blessed day.

Robert Jordan_3
11/23/2007 12:00:00 AM
GClark: Thank you for your kind comment. As someone who installs foam and someone who started with soy foam, I have reservations about the product. I was never able to get a MSDS from the company I was buying from and started to wonder if they had actually tested it to meet code requirements. Secondly, there is so little soy in it, it is hard to call it "green" for tht reason. Most foams had always had agricultural content in the form of alcohol distilled from sugar beets.

G Clark_1
11/10/2007 12:00:00 AM
Great job on the comment RJordan, couldn't have said it better myself. And there are "green" spray foams made from soy so that's even better.

Robert Jordan_3
7/19/2007 12:00:00 AM
A SIGNIFICANT cause of heat loss is air infiltration. Before adding insulation to the attic, it is ESSENTIAL to seal air leaks. Why don't articles ever mention this? R-value is like EPA MPG figures. That is, they are determined in a laboratory and have little to do with actual performance. Fiberglass is rated at 70 degrees. At temperatures one cares about, say 10 degrees, there is considerable degradation in its performance. It is impossible to seal air leaks in fiberglass. Pick up a piece in your attic and see all of the dirt on it. This is air moving through it, carrying your heat and filtering out the dirt. Even with air sealing, fiberglass is a problem. The best is spray foam as it seals and insulates and you get the full R-value. Second best is to do the preliminary work of air sealing and then adding cellulose. Unfortunately, it takes someone with experience to identify the leaks.

Atanacio Luna
7/18/2007 12:00:00 AM
A huge factor for my building was painting the roof. We had composition shingles, too dark, and heat is a big factor. We got oops paint from big building supply at a quarter of the price, and mixed it to get one color that was somewhat agreable. It will get dirty so exact match does not matter too much. The paint made the rooms a lot cooler. Workshop, with no ceiling was cooler than outside whereas before painting it was much hotter, plus it protects the shingles too. People commented that it looked good on their own, including RE agent when I sold buildings.

John Cady_2
7/17/2007 12:00:00 AM
When adding insulation and you live in an area that gets snow keep in mind that the roof may not have heat escaping out of your house. If you get extended amounts of snow you will have to watch for snow build up on your roof. I once had the snow reach 3 feet on my roof and had to shovel off the roof to prevent it from collapsing on us.

Neal Keller
7/17/2007 12:00:00 AM
you mentioned in your article that fiberglass insulation is fireproof. Fiberglass may be fireproof but the binder resins are quite flammable. Throw a square on your next campfire and watch it burn.








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