Insulation R-Value
Attics and Basements, Green Home, Heating and Cooling, Insulation, Interior by Ben Erickson
How well insulation works is expressed by its R-value, which measures resistance to the flow of heat. The higher the R-value, the better it insulates.
How Much Is Enough?
The amount of insulation recommended for your home is dependent on where you live, but here are some general guidelines:
- Attic: Houses in a cold climate should have a minimum of R-49 in the attic, which is equivalent to approximately 15″ of fiberglass insulation. Warmer climates only require an R-38, or about 12″.
- Walls: While wall insulation is limited by the width of the studs, different materials provide higher or lower R-values. Fiberglass batts for standard 2×4 walls are now available in low, medium, and high density products that range from R-11 to R-15. Sprayed foam insulation in the same wall cavity can range from an R-14 to an R-28 depending on the product that is used.
- Floors: While there are additional considerations—such as venting and moisture problems—to take into account when you insulate under floors, the United States Department of Energy recommends an R-25 rating in cold climates and an R-11 in warmer parts of the country.
Comparative Insulation R-Values
The R-value per inch for different types of insulation varies depending on the brand and how it was installed, but here are some general comparisons from the Department of Energy:
| Fiberglass (batts): | 2.9 – 3.8 |
| Cotton (batts): | 3.0 – 3.7 |
| Fiberglass (loose): | 2.2 – 2.9 |
| Cellulose (loose): | 3.1 – 3.8 |
| Rock wool (loose): | 2.2 – 3.3 |
| Cementitious (foam): | 2.0 – 3.9 |
| Phenolic (foam): | 4.4 – 8.2 |
| Polyisocyanurate (foam): | 5.6 – 8.0 |
| Polyurethane (foam): | 5.6 – 8.0 |
| Polyicynene (foam): | 3.6 – 4.3 |
Installing Installation
You can hire a professional to blow in loose insulation, or you can install rolls and batts yourself. If the attic isn’t insulated, cut the batts to fit in the space between the ceiling joists. If there is already insulation up to the top of the joists, roll out the new batts perpendicular to the joists.
If you choose to do the work yourself be sure to wear a long sleeve shirt, gloves, eye protection, and a particle mask. Don’t attempt to work in the attic during the heat of the summer, and be careful not to step through the ceiling!
Further Information
For more information on insulation and R-value from the U.S. Department of Energy:
- Energy Savers Tips on Insulation (map with R-values for each zone)
- Types of Insulation
- Insulation Fact Sheet
- Guide to Insulation and Air Sealing
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10 Comments on “Insulation R-Value”
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August 31st, 2007 at 3:10 pm
I prefer the ‘Johns Manville’ insulation over the ‘Pink’ insulation ,as the Johns Manville does not have as many loose itchy particles.
But still wear the appropriate attire.
September 13th, 2007 at 1:00 pm
Insulation R-value is only valid in still air. If you have a breeze going through your attic from soffit or roof vents it will degrade the R-value of exposed fiberglass insulation. The best results are gained by decking over the insulation, using a sheet product over exposed fiberglass insulation, or sealing up the attic completely and using a foam product under the roof deck to make the attic an enclosed space.
Ben Erickson Says:September 13th, 2007 at 2:26 pm
A valid point, but I would be concerned that a sheet product, like plastic, on top of attic insulation could cause condensation to form under it in the winter.
September 14th, 2007 at 4:37 pm
There are some sheet products I have heard about that are perforated to prevent becoming a vapor barrier. I don’t recall any brand names, but they were advertised for just this use.
October 8th, 2007 at 9:06 am
I am Finishing my basement and have come across moisture in the insulation that is wrapped around the basement walls and is wondering if that is common, also what I should do about it?
October 20th, 2007 at 4:03 pm
If you have visible moisture in a fully enclosed under ground basement.
1 .Is it a new house?
2. Is the moisture beads of water? or dark wet spots?
3. Do the walls have white efflorecencent
( salts in the water that form on the surface) lines on the walls: which would be from outside in?
If # 3 is yes than the water is coming from the ground and the water proofing is compromised on the exterior of the concrete wall, in which you need to stop the water.
If # 2 is yes then the moisture is condensation from the inside,which can be altered by a dehumidifier.
Over all the source needs to be determined so you know what to fix.
John Cannamela
http://www.infraredsurvey.com
November 24th, 2007 at 1:11 pm
i have 1500sq ft of attic space. thier is very little insulation in thier now. i was told blown in cellulose is better than roll in insulation. is that true? which is better and cheaper and easier to put in myself.i know how to blow insulation but im confused whick one or the other would be energy efficient as well as savings for my home. i also have a full crawl space under my house. do i use roll in insulation or what? and how much would it take and cost in material?
November 28th, 2007 at 4:27 pm
I’m trying to add insulation to my home. It was built in ‘81 and is raised about 36″ off the ground. I want to insulate the floors, but am just figuring all this out. What would be the best thing to use under the house? Is 3/4″ expanded polystyrene (R-2.9) good to use? Do I just nail/staple it to the bottom of the house? Any suggestions are welcome since I really have no idea what I’m doing…
December 1st, 2007 at 11:13 pm
Lani H and others
Te insulation that is there now may or may not me adequate, so add to it-use reflective backed foam board if in doubt- alter the seams then tape them with foil tape.you can’t loose.
Don- blown in is great however you will have more control over the batting and if you ever store stuff in the area ,it won’t ge moved out of the way so easy.Which helps to
know how much has been compromise in case a tradesmen has to work in the area at a later date.Bating is more likly to get put back than that fluffy stuff.
sometimes you need to think of what would happen if you are not there because noone will worry as much as you about your house.
I hope I helped an not confused anybody
Thanks again Danny for a great site
John Cannamela
http://www.infraredsurvey.com
Charlotte, NC
November 2nd, 2009 at 7:38 am
Can you please send me the Fiberglass Insulation K-Value vs. R-Value Comparison Fact Sheets?
Thanks.