Cellulose Attic Insulation
Insulating Attics with Blown In Cellulose Insulation
Today I’d like to tell you about the cellulose attic insulation being installed in the Energy Star home that we’re building for a client. Blown-in cellulose insulation is an excellent way to insulate your attic space. In my opinion blown-in cellulose is a much better product compared to fiberglass insulation.
Cellulose insulation is made from recycled newspapers. By using a recycled 
material cellulose insulation is certainly a very green building product! The recycled newspaper is treated with chemicals such as sodium borate, boric acid and ammonium sulfate to make it fire retardant. The chemicals also help make the cellulose insect, rodent and mold resistant.
As you can see in the photos we’re blowing the cellulose into the attic space with a flexible hose. The insulation sub-contractor has a special box truck with a giant blower system and hopper. The guys dump the cellulose into the hopper and it’s blown up through the hose into the attic. This is a really dirty job and one that requires proper breathing and eye protection.
Blown in cellulose out performs fiberglass for several reasons. However, the most obvious advantage is the ability to blow cellulose all around penetrations, framing materials, light fixtures and obstructions.
If this attic was insulated with fiberglass batts, it would have voids above each truss bottom chord member. With blown in cellulose you have insulation surrounding every single framing member and utility.
Cellulose achieves an R value of approximately 3.5 per inch. In this house we’re installing a minimum of 15″ of cellulose with a settled depth of 14″ for an R value of 49. Around here the minimum R value by code is 38 (for most situations). So you can see by using the cellulose we’re achieving an R value that’s almost 30% better than the insulation required by code.
So if you’re building a new home or thinking about adding additional insulation to your attic then I suggest you look into blown in cellulose insulation. I have it in my new home and every house we’ve built that has it out performs the houses with fiberglass.
How do you feel about blown-in fiberglass insulation? I just had Owens Corning Pro Pink blown into my attic.
@ Jayne – I honestly don’t have much experience with it. However, cellulose is safer for the environment and it’s a recycled product.
Some people feel that fiberglass can be a health hazard if it gets airborne in your home.
I was recently in an attic with blown in insulation. I think it was cellulose – white and fluffy – and man was I ever sorry I didn’t wear my respirator in there. I was coughing for hours afterward. I figured the house was only a couple years old and the new insulation wasn’t going to be too bad. I’ve been in attics with blown in fiberglass and found it to be fine. Another factor to consider if you ever decide to renovate that section the blown in stuff goes everywhere.
I have heard the concerns about the man-made fiber (fiberglass) and how it is handled by your lungs. Somewhat similar to how the asbestos fiber is too long to be removed by the cells in your lungs.
All insulation has it’s draw backs though if I had to do my own attic I’d go with a 1″ layer of spray foam and then do mineral wool batt insulation over top. The treated newpaper isn’t going to tolerate water well so if you have a leak your fire retardant will just wash right out of the newspaper and leave you with a flamable, mold inviting, rodent friendly section of insulation. Mineral wool is just volcanic rock so apart from having to be mined – not exactly sure where they get it – it is pretty environmentally friendly. It is still dusty but no where near as bad as my experience with the cellulose – not to say that all blown in is going to be bad and if you keep the water out of the attic and don’t use it for storage or even want to go up there probably best to choose whatever is going to perform the best and save you the most money over the long run.
@ Ian – I tend you disagree with your assessment in some ways. First of all that white fluffy stuff was actually a blown in fiberglass insulation in my opinion. I’ve worked in tons of houses with cellulose and I never cough. I almost always cough in an attic with fiberglass.
Secondly, cellulose is treated with mold inhibitors and fire retardant that is not effected by moisture. I know this is true because the dense pack cellulose we blow in the wall cavities has water in it in order to spray it.
I do however agree that spray foam is the best solution. However, when you compare it dollar for dollar cellulose is the best bang for your buck hands down (in my opinion).
Cellulose looks interesting, but it is heavy. Since the I have drywall over lathe and plaster, mounted on 2×2’s spaced on 24″ centers, the weight is an issue. I think I’m leaning towards fiberglass for this reason only.
@ Corey – Actually, cellulose is rather light.
Todd, I am considering using cellulose for my exterior walls and ceiling joists. I have also looked into using foam on the roof decking between the rafters. I have been told that the recommended application is to spray the foam directly to the roof deck with no ventilation space. I have called a roofing manufacturer and was told that for the time being this will not void the warranty on the shingles. Should I be concerned that with no way to remove heat from the back side of the roof deck, that the shingles will be “cooked” by the radiant heat of the sun? If I save on energy bills but have to change my roof every 3 to 5 years, I’m no better off. Fiberglass batts may be less effective, but with the right amount of insulation between the ceiling joists maybe this is a suitable alternative. Would you agree?
@ Joe – I think you’ll be fine. Most experts are starting to recommend no ventilation with foam spray. I think your shingles will be fine!
for wall insulation, i always use polyethylene foams and also polypropylene foams;'”
Since adding about 6″ of blown cellulose insulation to an existing 6″ of cellulose in attic, I am finding cellulose dust particles coating my entire interior floor and furniture after a week’s period. While I can access the attic, the shallow pitched roof only allows limited access to about 2/3rd of the attic area. I highly suspect the cellulose particles are finding their way into the room through the IC rated retro/remodel canned lighting fixtures in ceiling. Any suggestions to mitigate?
Do you have any duct work in the attic? A/C….attic vent? It’s not uncommon to have this type of situation right after having insulation blown in. It typically goes away after a short period.
A couple of people have mentioned that they would not blow cellulose over fiberglass in an atic as it compresses the fiberglass and reduces the R-value. What is your thought on this? Is it better to suck out the older fiberglass and replace it with all cellulose?
Also will a few cans of spray foam work best to seal the areas around HVAC vents pipes in the attic? This will help prevent heat/AC loss.
By the way I live in Souther Alabama, if that helps.
Nate
Blowing in additional insulation over older insulation is done every day here in the Northeast. Sure it’s going to compress it but the only important issue is the total depth when they are finished. The compressing will happen almost immediately. It’s really not an issue in my book.
Yes on the spray foam!
My air conditioner is in the attic. The attic is only 36″ high, at the peak, has a R19 (fiberglass), and in the summer the temperature, up there, gets to be 25 degrees hotter that the outside temperature. I have noticed that the condensation on the ducts is excessive. I am concerned that all of the condensation will eventually get to the dry wall below. Is there any way that I would be able to control this condensation? The ducts already are all wrapped and taped. It would be move the air conditioner blower to another level of the house, but unfortunately, that is not an option.
The only real way to do this is to insulate the duct work more and reduce the attic temperature.