Recycled Insulation And Energy Efficiency: Cellulose

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All insulation is green, but cellulose has more eco-friendly properties than most. Here is a breakdown of the energy efficiency advantages it presents.


Insulation, by its nature, is eco-friendly. It saves energy by preventing airflow through walls, floors, and ceilings. Heat stays inside in winter and outside in summer. Reducing energy use equates to cutting back on fossil fuels and saving natural resources.

The old insulation standby is fiberglass, and all other insulating materials are measured against it, since there is so much known about it. It’s also a good base to work from when trying to find insulation that is more eco-friendly in manufacture, installation, and performance. Cellulose has fiberglass beat in all those categories.

Green properties

Cellulose is recycled paper. Newsprint, white paper, and cardboard are mechanically shredded, or fiberized, keeping this trash out of the landfill. Boric acid is added as a fire retardant, but is also effective for insect and mold resistance. The mixture is approximately 85% paper and 15% borates.

Adding ammonium sulfate is optional. Because cellulose is viewed as a green building material, the ammonium sulfate makes it less so. Cellulose contains no formaldehyde, which is found in many traditional insulating materials.

Cellulose is not energy intensive to make, using about 15% of the energy it takes to produce fiberglass. Its largest environmental cost is transportation from the factory to your home. Installation is possibly a DIY project, especially to blow loose fill into an attic or crawl space. I was on a job site once where they were making and applying their own cellulose. In that case, it uses very locally sourced materials! For best results, though, hiring a professional contractor is recommended.


Insulation is measure by R-value per inch, R meaning resistance to heat flow. The higher the number, the more effective the insulation. When properly installed, cellulose has an R-value of 3.5-4, which is higher than average in comparison to other products. It can cut energy bills 20-30% more than fiberglass.

Cellulose insulation can be used in homes seeking LEED certification. It is non-toxic and uses no HFCs in spraying.

Loose fill

Cellulose can be applied to walls, floors, and ceilings in new construction and renovations. Different types are used for the various applications.

Loose fill is best for remodeling. It can be blown into existing walls by removing a bit of exterior siding, drilling holes in each stud cavity, and blowing in the cellulose. Filled to 3.5 pounds per cubic foot (called dense-pack), it will perform the best by not settling. The density creates a tension in the wall cavity that keeps the material from sagging.

Dense packed loose fill gets into hard to reach places, and completely surrounds plumbing, electrical wires, ductwork, and outlets. It works where batts of other materials can’t, further cutting drafts.

blown in cellulose insulation

(image: Ryo Chijiiwa)

Wet spray

Wet spray cellulose has a bit of water added to it to help it adhere to the surfaces. It is best for new construction when the inside of a wall is completely exposed. The spray goes right up against the exterior sheathing to reduce thermal bridging, where much heat is lost. It also seals joints where studs meet the wall.

Cellulose needs no vapor barrier, because it manages moisture on its own. It is so tightly installed that there is little air movement, so vapor cannot invade it. Cellulose also wicks moisture and spreads it throughout the wall cavity preventing pooling. The wall must breathe, so a vapor barrier can cause mold.


If cellulose is not installed densely enough, it will sag and settle, reducing its effectiveness. This is why a professional should be hired. They have the right equipment to pack it correctly.

It will also sag and pack down if it gets very wet from a major or constant leak.

Cellulose is heavy. Ceilings should not be compromised at all in attic installations.

If ammonium sulfate has been added, it may off-gas. If the insulation stays wet, say from a long-term leak, the borates might corrode screws, plumbing and wiring.

Making a choice

Fiberglass is good insulation. If it weren’t, it wouldn’t have been around for so long. It’s easy to find, inexpensive, and easy for a homeowner to install.

Cellulose is good insulation, too. It performs better than fiberglass, and has less embodied energy. It’s a good idea to hire a professional installer, but it still has a high and quick return on investment.

It comes down to personal choices of your own carbon footprint and your sense of adventure to try something different. Me? I’m the adventurous one. How about you?

For more information on cellulose, check out CIMA, the Cellulose Insulation Manufacturers Association.

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Nan Fischer

Nan Fischer has been living and building green for over 35 years. Nan’s emphasis on the BuildDirect blog is about how to make your dollar stretch further, while also moving toward a more sustainable lifestyle, as well as upcoming and existing technology to help us live in an ecologically-friendly way. Nan also authors posts on the website of her seed business, sweetly seeds.