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Blown In Cellulose – The Ultimate “Green” Insulation?

by Chad Ludeman on August 16, 2010 · 24 comments

in envelope,materials

In my last post about super-insulated wall assemblies, I referenced a future post about the superiority of Dense-pack Blown-in Cellulose insulation over other insulating products. Well, this is that post. We’ve talked about insulation in the past, but after extensive research and pitches from other insulation fanatics we’d like to put Cellulose in the spotlight as what we consider to be the best insulation product on the market today.

Dense pack blown in cellulose in Skinny

Why is Blown-In Cellulose so awesome in bullet point format:

  • Inexpensive – It’s not as cheap as Fiberglass, but it’s much more reasonable than rigid and spray foam options.
  • Lowest Embodied Energy – Of all the types of insulation, cellulose takes the least energy to produce. It is recycled newspaper after all and often it is locally sourced and manufactured.
  • Fills all gaps – While batts will leave many gaps around electrical wires and boxes and will not always hug the studs, blown-in cellulose fills every available gap when installed properly.
  • Air Retarder - Air leaks in your homes walls and roof can cause significant losses in efficiency. Cellulose significantly resists the flow of air through your walls and maintains it’s rated R-value even in heavy gusts. This feature also makes cellulose a great fire retardant compared to batts.
  • Maintains R value – We hinted at this in the last point, but cellulose is exceptional at maintaining its advertised R value. Fiberglass wilts in the face of wind and extreme temperature difference between inside and outside.
  • High thermal mass – It’s not called dense-pack for no reason. Cellulose adds thermal mass to your walls that has been proven to help a home maintain its temperature (pdf) for days longer than a similar home insulated to the same R-values with fiberglass.

These are the reasons we have come to love cellulose. It’s not just us though. Search around. More and more super-insulated and Passive Houses are switching to cellulose all over the world.

For a more detailed comparison of insulation products, check out this table at Did we miss anything? Let us know in the comments.

If you enjoyed reading this post I can promise you'll love our new writing over at Postgreen Homes. Yeah, we know that's the same thing your favorite band said and their new album is nowhere near as good as their early stuff, but seriously, we are actually still getting better.

There also isn't much conversation to be had here . . . at least not with us. So come on over to the Postgreen Homes Blog and tell us what you think of our new(ish) digs and crazy ideas. We will be sure to tell you what we think of your opinion.

{ 3 trackbacks }

Most Affordable & Effective Super-Insulated Wall Assembly? — 100K House Blog
August 16, 2010 at 8:18 pm
Discussion : Insulation | Meek's Design Center
September 13, 2010 at 12:17 pm
Cutting Cellulose Insulation Install Costs? — 100K House Blog
October 12, 2010 at 10:01 am

{ 21 comments… read them below or add one }

1 Gene August 16, 2010 at 8:27 pm

The only possible problem I’ve heard of is settling. But I haven’t seen any evidence of that, just concerns over it. Are there any studies showing longer-term performance WRT settling within the wall cavity?

2 mike eliason August 16, 2010 at 11:39 pm

can this be amended to roofs and certain wall types?

while dense pack is great for what it does, it’s usefulness in say, an under-slab condition, leaves a lot to be desired.

also, there are certain wall assemblies where cellulose isn’t as preferable as mineral wool or similar (e.g. masonry, certain rain screen applications, etc)

the only insulation with less embodied energy that we’ve come across is cork, not really viable for a wall assembly, though.

if looking at the total LCA of cellulose, though – i’m a little leary that dense pack is as ‘green’ as suggests… having lived near a paper plant, the process of manufacturing paper and newsprint has gotten better, but it sure ain’t pretty.

gene – if you are superinsulating w/ dense pack and go around with FLIR, you can catch the voids that need to be filled.

3 Emmanuel August 17, 2010 at 7:51 am

Cellulose also exists in sheets. Is it as effective?

4 Chad Ludeman August 17, 2010 at 8:22 am

Agreed, we are referring to walls, roofs and floors here. Any basement or sub-slab insulation would be in a different category.

While the production of paper may be dirty, it doesn’t impact the fact that cellulose is made from 100% post-consumer product.

Proper installation of dense pack is key. You can’t just hire anyone to do it. A lot of the bad comments on the web come from improper installs decades ago when it was just first catching on. Our installer actually comes back with an IR camera to ensure none of the walls have settled. If he finds one that has, it is usually from an owner or alternate sub making a change within the wall and removing insulation. He will then come back and refill the top of the cavity as needed.

5 Dan August 17, 2010 at 12:22 pm

You didn’t mention anything about fire. Cellulose is treated so that it is quite fire resistent. Most things will burn when exposed to flames for long enough including other insulating materials, however. The good news is that cellulose is much less toxic when this happens than the common alternatives. I’m using cellulose in the home I’m building for this reason and all the ones you’ve mentioned.

I’ve also understand that it is a good sound attenuator, but not sure how it compares to other insulation materials.

Nice article!

6 mike eliason August 17, 2010 at 3:54 pm


the CIMA website says it’s only 85% recycled content.

CIMA previously claimed that insulating a house with cellulose will recycle as much newspaper as an individual will consume in 40 years.

they must have been talking about a podunk weekly gazette, and not a major paper like the NYT, which would come in at a staggering 10+ tons over 40 years…

7 Tim Capaldi August 18, 2010 at 3:07 pm

Chad -
I agree. The Cellulose is a great product. We use it on a ton of our projects both remods and new builds. I put it in my own house 6 years ago and couldn’t be happier. It’s also key to make sure (depending on your location and climate conditions) you have good attic ventilation. Proper installation of the Cellulose along with the ventilation in the attic and you’ll have a very happy customer.
You guys do a great job with the Blog.

8 Gary S August 25, 2010 at 10:09 pm


Would you mind sharing with us what you’re paying per installed board-ft (or however it’s priced) for dense pack? We’ve done a lot of new construction and reno projects here in northern NJ with closed cell foam. While we’re pleased with the product’s performance, it’s spendy at ~$1.00/bf, and our experience with contractors hasn’t been great. We’ve considered cellulose, but never got to the point of talking numbers with contractors.

9 Chad Ludeman August 25, 2010 at 10:55 pm

Gary – That will take some calculating, but I’ll see what I can do. Definitely will be cheaper by at least half if I had to guess. Give me a week or so.

10 Dan S. October 14, 2010 at 6:46 am

Chad, Did you come up with a cost in the end?

How does cellulose perform with moisture in a tightly sealed wall cavity? I gather moisture may dew up or crystallize on a strand of fiberglass, but does cellulose simply absorb it?

11 Robert Riversong December 20, 2010 at 4:44 pm

I’ll ditto the low-embodied energy and life-cycle-cost of cellulose insulation. While the best cellulose on the market is post-industrial recycled (not post-consumer because it’s too dirty), the 85% figure is because 15% is borate fire retardant (also low embodied energy and non-toxic). Do not use cellulose treated with ammonium sulfate which is corrosive to metal and may offgas (like the Chinese drywall) when damp.

Because the manufacture of cellulose insulation keeps newsprint out of our landfills, which are 45% filled with paper products, it actually has a profoundly positive environmental impact and a negative life-cycle cost when all externalities are considered. It is also a way to sequester carbon for the life of a house.

I have to correct the blog, though, about the thermal mass benefit of cellulose. While it’s relatively high density makes it a far better air barrier and a better acoustic barrier than lower density fibrous insulations, it does not serve as thermal mass. To function as thermal mass requires the much higher densities of drywall (40 pcf), water (62.4 pcf) or concrete (150 pcf), as well as high volumetric heat capacity and moderate thermal conductivity. Cellulose has none of those qualities.

But an additional quality that was not mentioned is that the borates, while non-toxic to humans and pets, are deadly to all common household insects and will deter rodents as well. It is the only common insulation which has this extremely important side benefit.

Also, the highly hygroscopic quality of cellulose allows it to safely absorb and release up to 30% of its weight in water, allowing it to function as a moisture buffer (much like thermal mass does for excess heat) and help control indoor relative humidity. Because it absorbs and redistributes moisture so quickly, it will actually protect wood framing from leaks or condensation by wicking the water away from the wood and distributing it over a much larger volume, thereby lowering the moisture content and the probability of mold or decay. No other insulation offers this benefit.

12 Chad Ludeman December 20, 2010 at 4:50 pm

Robert – Thanks for the comments. What is your thinking on the linked PDF showing the perceived benefits of higher thermal mass in the cellulose test homes compared to the fiberglass homes? Maybe the mass is not nearly as high as typical materials used to increase thermal mass, but is it having a noticeable effect compared to fiberglass and the study reports?

13 Robert Riversong December 20, 2010 at 6:22 pm

Chad, That link is to a publication of the cellulose manufacturer’s trade association, which tends to be much more reliable than the fiberglass trade association (NAIMA), even though it can’t be considered objective.

But the document makes no claim about the thermal mass value of cellulose. It mentions thermal mass as one of the several elements that must be considered in determining the overall thermal efficiency of a building envelope, though it fails to mention that the location of the thermal mass makes all the difference.

14 Tim Miller January 8, 2011 at 3:24 pm

Howdy, Im Renovating a105 yer old home and am installing a staggered stud wall to allow super insulation with cellulose. Any one comment on installing 1/2″ 4by8′ insulation sheets on the inside wall behind the drywall or between the two stud walls verses installing 2″ foam to the exterior – in my life the 2″ is too $$.

15 Robert Riversong January 8, 2011 at 4:14 pm


The ½” foam board will add little additional insulating value and is not necessary to reduce thermal bridging since that’s take care of by the staggered studs. But if the foam is foil-faced it will act as a near perfect vapor barrier which will prevent any drying to the interior. You’d be better off by increasing the depth of the wall cavity for additional cellulose and concentrating on an air-tight inner drywall “skin” with a vapor retarder primer.

You don’t say what climate zone you’re in or how thick you’re making the new walls, but make sure that you at least meet the current DOE/IECC R-value standards for your zone.

16 Tim Miller January 24, 2011 at 1:32 pm

Howdy Robert, thanks for answering my question about using foam insulation board. I am interested using cellulose in a 10″ staggered double stud wall but also concerned moisture vapor diffusion. Cannot find information about how or if two thick of wall insulation & moisture ? Home in cold zone #5 up to -20 in winter. Did find an interesting article on BTU savings verses cost of insulation but cellulose was not included. Just fiberglass or foam. Anyone aware of this type of information when comparing cellulose?

17 Robert Riversong January 24, 2011 at 2:12 pm


I can’t make sense of your question. Can you restate it more clearly?

18 Tim Miller January 24, 2011 at 4:12 pm

Sorry Robert My concern is if there wall is too wide filled with cellulose can the moisture vapor not be able to travel threw it an lead to rot/ mold issues? The second question is the cost verse benefits of making a wider wall or double wall filled with cellulose compared to a 51/2″ wall cavity filled with cellulose?

19 Robert Riversong January 24, 2011 at 5:30 pm

The issue is not the thickness of the cellulose, but the vapor permeance of the outer “skin” of the house. If the outside can breathe, and the indoor moisture is controlled with bath and kitchen exhaust fans and whole-house ventilation, then there will be no moisture problem.

A double stud wall filled with dense-pack cellulose is the most cost-effective (and green and healthy) way to achieve high levels of energy efficiency.

20 Karl August 6, 2012 at 3:24 pm

Great article about blown in insulation. I learned a lot from reading. Keep up the good work.

21 Josh August 16, 2012 at 6:03 pm

What is the average turn time per sq ft in re-cooping the added cost in comparison with fiberglass?

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