Reuben Saltzman

Attic insulation types

What’s the best attic insulation? That depends on your definition of “best”. What’s going to perform the best is definitely not the most cost-effective way to insulate an attic. But surely, you already knew that.

And I didn’t call you Shirley.

First, let’s discuss the most common types of insulation available for attics; spray foam, loose-fill fiberglass, cellulose, and fiberglass batts. Those aren’t the only types available, but they make up the vast majority of what’s used in Minnesota attics. For the listed R-values below, this refers to the material’s ability to resist the transfer of heat and is all per-inch. The higher the number, the better. The minimum R-value for a new Minnesota attic is R-49.

Fiberglass Batts

Unfortunately, the easiest way to add insulation to just about any place in your home is to install fiberglass batts.  Fiberglass batts are typically the worst insulation for any job, but they’re easy to pick up in the store and easy to roll out, so people use them. The image below shows an atrocious installation at a two-year-old home in an upscale neighborhood of an inner-ring suburb of the Twin Cities. Yep, this passed the city inspection.

Botched fiberglass batts in attic

I won’t even discuss R-value because fiberglass batts have no place in an attic. Just don’t go there.


Cellulose insulation

Cellulose is made from recycled, ground-up paper with boric acid added for insect control and fire resistance.  If you choose to install cellulose yourself, you can buy the insulation in bags from your local home improvement store. If you buy enough, they’ll probably let you use an insulation blower for free. Don’t try to buy a single bag and spread it out by hand for spot-insulation; it’s way too densely packed (ask me how I know). The DIY cellulose insulation method is very dusty, but it’ll get the job done.  If you hire a pro, they’ll use wet-spray cellulose, which adds a small amount of water to the cellulose to help control the dust and to slightly increase the insulation value per inch.

Cellulose has an R-value of approximately 3.5 per inch. The part that I love about cellulose is its ability to control air movement. While it doesn’t actually create an air barrier, it’s dense enough to stop most air movement to help control frost in attics. Not completely, of course, but it does a pretty good job. The same cannot be said for fiberglass.

If you check with the Cellulose Insulation Manufacturers Association, they’ll assure you that cellulose is definitely your best choice for insulation.

Loose-fill fiberglass

Loose-Fill fiberglass insulation

This seems to be all that’s ever used in new-construction homes and has an R-value of approximately 2.5 per inch. Like cellulose, you need a big machine to blow it in. You can’t simply buy it in bags and spread it around yourself. My biggest complaint with fiberglass is that it’s itchy and it’s a lung irritant. I’ve found that older fiberglass is way worse on your skin and lungs than the newer stuff, however. I have no scientific evidence to back this up, but I don’t need any. I’m completely sure of this based on personal experience.Facemask

Side note: I wouldn’t dream of doing any type of insulation work without wearing a respirator. Heck, I won’t even enter an attic without one.

There was a widely publicized study conducted by Oak Ridge Laboratories in 1991 that said that loose fill fiberglass insulation lost a lot of its insulation value once temperatures dropped below 20 degrees, making loose fill fiberglass an inferior product when compared to cellulose.  I contacted Andre Omer Desjarlais at Oak Ridge Laboratories about this issue, and he said: “This was true 20 years ago but all fiberglass manufacturers have changed their products appreciably since then and this is simply no longer an issue.”  I also contacted several insulation manufacturers about this, and they said the same thing and sent me some great information, which I posted on my website many years ago; click any of these links to read the documents from CertainteedJohns Manville, or Owens Corning.  Loose fill fiberglass insulation will still experience convection, but not nearly as much as old fiberglass used to.

If you check with the North American Insulation Manufacturers Association, they’ll assure you that fiberglass or mineral wool is definitely your best choice for insulation.

Spray foam

From a performance standpoint, the best type of insulation is spray foam. There are two types; closed-cell and open-cell, aka 2-lb and ½-lb, respectively. They have insulation values of approximately R-6.5 and R-3.6 per inch, respectively. When installed properly, both types of insulation will fill all of the nooks and crannies and make for a perfect air barrier. When air can’t move through it, you have zero heat transfer through convection. Oh, and by the way, Icynene® is a brand name of open cell foam.

With closed-cell foam, you also get a moisture barrier at over 2″ thick. Because of this and the higher insulating value per inch, most foam insulation used in Minnesota is closed-cell. To tell the difference between the two, try poking it with your finger. You can easily poke a hole in open cell foam, but not closed-cell foam. That stuff is way too hard.

The big downside to either type of spray foam insulation is the cost. It’s expensive stuff, and it shouldn’t be installed by the DIYer. Of course, that’s not to say it can’t be done, it just shouldn’t be done. Professionals already have a hard enough time getting it right. Check out this article for more on that topic: Avoiding Problems With Spray Foam. The image below shows a botched spray foam installation at the rim joist of a new-construction home that I inspected.

Botched spray-foam insulation

A concern with spray foam insulation is the off-gassing of toxic poisons. I’m no expert on that matter, so I won’t discuss. Just be aware that it’s a concern, and do your own research. After conducting my own research, I concluded that I was comfortable putting it in my own home.

What’s next

So now that I’ve covered the products, the next part of this discussion is what to do with them. I’ll discuss that next week.

Author: Reuben SaltzmanStructure Tech Home Inspections

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No responses to “Attic insulation types”

  1. Hank
    January 30, 2018, 9:00 am

    Great blog post Reuben.

  2. Reuben Saltzman
    January 31, 2018, 5:54 am

    Thanks, Hank .

  3. Joanna Hoerr
    January 30, 2018, 10:17 am

    Hi Ruben,
    I need to tell you I really enjoy your blog posts. We are remodeling Bridget’s house and I am learning a lot. You have a great sense of humor and make the topics easy to understand!

    Thanks for all the info,

  4. Reuben Saltzman
    January 31, 2018, 5:53 am

    Thanks Joanna! Please say hi to Bridget for me.

  5. Alan Steinmetz
    January 30, 2018, 6:39 pm

    Good Information. Ill share it.

  6. Reuben Saltzman
    January 31, 2018, 5:53 am

    Thank you!

  7. jthomp
    January 30, 2018, 7:58 pm

    Ruben I would be interested in an article about how professionals should redo or reinsulate an attic in older (1950’s) homes . For example I have zonolite(vermiculite) covered with some older loose fill fiberglass which has settled .

  8. Reuben Saltzman
    January 31, 2018, 5:55 am

    Hi jthomp,

    That’ll be the focus of next week’s blog post, but I won’t be discussing vermiculite. Check out my blog post on vermiculite for information specific to that product:

  9. RD
    February 25, 2018, 10:04 pm

    Be aware that millions of attics in older homes and businesses still have vermiculite insulation in them and that the vermiculite insulation itself is contaminated by asbestos that the Mfr W.R. Grace KNEW for decades that their Libby Montana mine the stuff was mined from was contaminated, and it was sold under the “Zonolite” brand name!
    There are video documentaries on youtube about the whole scandal around W.R. Grace and their asbestos contaminated vermiculite insulation. When the lawsuits started coming in they filed for bankruptcy, left everyone holding the bag and reorganized as a “new” company still selling products today!
    Their mine and site was declared a superfund cleanup area, the entire town of Libbie Montana was contaminated by it, they let people take away waste tailings to use in gardens, the school used it on their running tracks, what a disaster!
    I would never buy a house with that stuff in the attic, you can never fully get rid of every bit of it and it’s said to cost $20,000 and more to get it removed from the attic, but then you are dependent on some guy in the attic with the vac machine doing an excellent job out of sight.

  10. Greg Cotton
    February 1, 2018, 1:53 pm

    When I did my attic I did a good job of insulating the 2nd floor ceiling/attic floor with the existing 6 inches of cellulose and fiberglass that was already there with some additional to fill gaps.

    The roof and end walls were done with 4 inches of closed cell foam with 1/2 inch of foil covered foam board over the studs for additional insulation and a thermal break over the rafter 2x4s. I paid close attention to keeping everything gap free and sealed and even foil taped the foam board seams. I added sheetrock and plaster over that. Even on sub-zero days the heatless attic never drops below 50 degrees. I open a couple of cast iron vents when I want heat up there.

    If I was going to build a new house it would be all foam insulation!

  11. Attic Insulation Methods - Structure Tech Home Inspections
    February 6, 2018, 6:00 am

    […] topics to cover; insulation types and insulation methods. Last week’s post was about insulation types, this week’s post is about insulation […]

  12. RD
    February 25, 2018, 9:59 pm

    Be aware that millions of attics in older homes and businesses still have vermiculite insulation in them and that the vermiculite insulation itself is contaminated by asbestos that the Mfr W.R. Grace KNEW for decades that their Libby Montana mine the stuff was mined from was contaminated.
    The stuff was shipped all over the country by rail and truck in paper bags, sold retail at hardware stores and other outlets for people to install it themselves. This contaminated the transport and delivery vehicles, stores, customer cars, clothes, and their homes. Furthermore, every time the attic is entered it stirs the dust up, it also migrates into the wall and ceiling cavities and can “filter out” thru the most minute cracks around outlets, switches, window trim and light fixtures.

  13. Peter friedlieb
    March 8, 2018, 10:38 am

    Hi Reuben,
    My daughter in northern Iowa is looking at attic insulation in her old home and currently has R27 cellulose but nothing for the eaves. Her contractor says she can’t use closed foam for the eaves because of the weight. The cost of adding cellulose to R49 and the separate cost of the open foam are about the same. They do get ice dams. If she was to chooses only one which would be the best way to go? No recessed lights.

  14. Reuben Saltzman
    March 8, 2018, 11:05 am

    Hi Peter,

    I don’t understand how the weight of closed cell foam would have any effect on anything. Personally, I’d get another opinion.

    If your daughter has cellulose added, what will be done to air seal the attic?

  15. Peter Friedlieb
    March 12, 2018, 4:57 pm

    Thanks Reuben,
    Since my daughter already has R29 cellulose, the cost to remove it all and seal the bypasses looks prohibitive. I’m wondering if she did closed foam at the eaves and since she’s needing a new roof that she put up a metal roof-it’s a steep pitch. Perhaps that would take care of the ice dams and still give her more needed insulation.

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