Insulation R-Value
Attics and Basements, Featured, Green Home, Heating and Cooling, Insulation, Interior by Danny Lipford
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 per inch of thickness.
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 Insulation: 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″.
- Wall Insulation: 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.
- Floor Insulation: 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:
| Insulation Type: | R-Value per Inch: |
|---|---|
| Fiberglass (loose) | 2.2 – 2.9 |
| Fiberglass (batts) | 2.9 – 3.8 |
| Cellulose (loose) | 3.1 – 3.8 |
| Rock Wool (loose) | 2.2 – 3.3 |
| Cotton (batts) | 3.0 – 3.7 |
| Cementitious (foam) | 2.0 – 3.9 |
| Polyicynene (foam) | 3.6 – 4.3 |
| Phenolic (foam) | 4.4 – 8.2 |
| Polyisocyanurate (foam) | 5.6 – 8.0 |
| Polyurethane (foam) | 5.6 – 8.0 |
Installing Installation
You can hire a pro to install insulation, or you can install insulation yourself in rolls and batts. If the attic doesn’t have any insulation, use faced insulation, with the vapor barrier facing toward the living space, and cut the batts to fit in the space between the ceiling joists. If the attic already has a layer of insulation up to the top of the joists, use unfaced insulation, with the new batts installed perpendicular to the joists.
Blown fiberglass or cellulose insulation is usually installed by an insulation contractor, but DIY blown cellulose insulation is also available. Loose fill cellulose insulation for blowing can be purchased at home centers and blowers are available to rent.
When installing insulation, wear:
- Gloves
- Goggles
- Long sleeve clothing
- Mask or respirator
Also, don’t work in the attic during the heat of the summer, and be careful not to step through the ceiling! Spaying expandable foam insulation is a job that should be left to professionals.
Spraying expanding foam insulation in walls
Further Information
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
Related Posts
- Attic Insulation (video)
- Getting Adequate Attic Insulation (article)
- Prevent Fiberglass Insulation Itch (video)
21 Comments on “Insulation R-Value”
You can follow comments to this article by subscribing to the RSS news feed with your favorite feed reader.
Leave a Comment
Comments submitted may be edited for clarity and used on Homefront, Today’s Homeowner®, or posted in articles on dannylipford.com at our discretion. In addition, you may submit questions at our contact page or by calling (800) 946-4420.
August 31st, 2007 at 15:10
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 13:00
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 14:26
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 16:37
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 09:06
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 16:03
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 13:11
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 16:27
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 23:13
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 07:38
Can you please send me the Fiberglass Insulation K-Value vs. R-Value Comparison Fact Sheets?
Thanks.
January 2nd, 2010 at 12:17
I need to insulate a 12×24 steel framed workshop. It’s a sweatbox in summer and an icebox in winter! I live in central Georgia. Any thoughts on how to best accomplish this and choice of insulation is greatly appreciated.
January 2nd, 2010 at 12:21
I forgot to mention that the building is clad in aluminum siding. Also, moisture control is important as my area is very humid most of the year
January 7th, 2010 at 16:40
I live in Raleigh North Carolina and would like to insulate my attic. My house is approximately 1600 sq feet and was built in 1963. The attic has had no upgrade of insulation since. It now has roughly 3 to 4 inches of blown cellouse insulation. I am leaning towards insulation of pink fiberglass with a R-38 rating. The thickness would be 12″ and a width of 16″. Is this enough insulation? I’m not sure of the square footage of the attic yet but I’m assuming it will take between 25 and 30 rolls. Thank you. Ellis Farris
January 10th, 2010 at 08:23
I inherited my grandfathers farmhouse built in 1900. Although I grew up playing there and visiting since then, it is now my responsibility to take care of it. We have spent the last year working on the obvious and last year we only had a fireplace for heat. After purchasing a propane tank I thought my heat problems were over, Wrong! After examining under the house with about a 16 inch crawlspace, I have discovered that there is no insulation or sub floor. Only hardwood floors over the 2X6 joists. I have been researching insulation and after seeing your show on the weather channel I still have questions. Would an R-19 with facing be sufficient? Also, since this is literally off the ground (no basement) should I enclose the insulation? It appears that I should put in batting face side to floor and am considering using a basic plywood across the joist. There are also insulated sheats that say they are indoor/outdoor with “R” ratings and they state that they even hold up to immersion in water, but I am unsure of these for an exterior surface. Since I have 6 inch joist, should my insulation be 6.5″ (R-19) and would the plywood or the insulated sheaths be best? How much improvement in comfort and utility bill should I expect? There is nothing blocking the wind from coming underneath the house. Thanks
Ben Erickson Says:January 11th, 2010 at 11:27
Hi Jenn,
If possible I would start by closing in the foundation around your home, then add insulation between the joists with 6″ insulation (which should be plenty), holding it in place with specially made support wires. Check out the article and video from our Scariest Utility Bill episode to see how to go about insulating under a floor.
January 12th, 2010 at 10:41
Hi Ben,
I can’t close in the foundation because there is a creek about 200 or so feet away; water has only entered the house once, during Hurricane Camille and only because of storm surge backed up all rivers and creeks. Just in case the creek were to ever rise that high again, I need water to have the ability to flow versus rising. I am going to check this weekend to verify if I have 2 x 6 or 2 x 8 joists and if they are 16 or 24″ centers so that I can buy the right size of insulation. If I buy faced and staple with facing close to floor, at most I will leave an inch and half from the bottom of the joists. This air flow should assist with moisture evaporation, so I think the 6.5 inch, R-19 will be ok. I am looking at osb board to put on the bottom of the joists, what do you think?
Also, I will ck this weekend to see how much, if any, insulation is in the attic. Since warm air rises, I think my first attack should be in the attic and then the floor. I used a calculator and it said to insulate to R-49 for this area. The farm is in Wayne County Mississippi about 5 miles from Millry Al. Currently, there is no attic access, but it has a metal roof. I am thinking of blowing insulation in by removing sections of roofing. Any advice would be appreciated.
Ben Erickson Says:January 13th, 2010 at 09:45
Jenn,
Since most heat and cool loss is through the attic, you’re right to tackle it first. If possible, it’s important to provide adequate ventilation in the attic to remove hot air and prevent condensation (see our articles on Attic Ventilation and Soffit Vents), which it sounds like would be hard to do in your case. As far as under the house goes, it would be okay to attach OSB to the bottom of your joists. You might want to screw them on with drywall screws and a cordless drill so you could easily take it off in case it floods and the insulation gets soaked. Good luck with your project!
January 21st, 2010 at 09:17
Thanks Ben!
My son and I got into the attic this past weekend and guess what we found??? NO Insulation whatsoever!!!! Just wood ceilings and rafters with Tin overhead! We have measured and are getting ready to get started. Most of the rafters are logs, the others 2×6. I plan to lay R-30 down first inside the logs (30″ in between so will use 2 x 15″ rolls)and go back another time and add more cross the logs. It appears that R-30 is no longer the standard minimum. Looks like R-38 to R-49 is more the current minimum. Since I have no insulation, I should see a huge difference in comfort and bills just from the R-30! Will tackle underneath later as you suggested. Thanks for your help. Now if you can tell me how to keep the pipes from freezing under the house, I am all ears!
Ben Erickson Says:January 21st, 2010 at 15:27
Jenn,
Keeping your pipes from freezing isn’t easy if the crawlspace under your house isn’t enclosed, but here are some tips:
Use pipe (like PEX) that resist breaking when the water freezes.
Bury the pipes and run them straight up to the plumbing fixtures to reduce the amount of pipe you need to insulate.
Wrap heat tape around hot and cold pipes (unplug when above freezing) followed by foam insulation.
Drip faucets when the weather is below freezing.
May 1st, 2010 at 19:28
I am finishing my basement and live in the foothills of NC. I have sealed the walls with three coats of drylock. My basement has always been fairly dry. I have 2×4 studs for walls. They are not in direct contact with the walls. Now to my question. Do I need to put insulation with paper face or no paper. Some people are telling me that the paper would trap moisture and paperless would allow it to breath. Im lost please help.
Ben Erickson Says:May 2nd, 2010 at 09:28
Hi Allen,
If your masonry basement walls are dry, I would use faced insulation, with the paper facing in toward the living space to prevent moisture from the warm inside air from condensing on the cool masonry walls.