What You Should Know About Blow-In Cellulose Insulation

The installation process for dry cellulose insulation looks like this:

What is Cellulose Insulation? What’s it Made of and How Does it Work?

Do you need insulation in your home, and you’re looking for more information on a more traditional material like cellulose?

Cellulose insulation is the oldest form of home insulation and is still found in homes today. It can be either a loose-fill or blown-in insulation and can be used in both new and existing homes.

RetroFoam of Michigan has been in the foam insulation game for more than 17 years. While foam is all we do, we know quite a bit about traditional insulations like cellulose.

We are on a mission to be transparent while educating homeowners on all things home insulation — even the materials we don’t install.

Now, let’s get started on this educational journey to learn about all the things you want to know about cellulose insulation.

What is Cellulose Insulation?

Cellulose is a fiber insulation used in enclosed existing walls, open new walls, and unfinished attic floors.

Several companies manufacture cellulose insulation, and it is primarily made from recycled newsprint.

These small particles form an insulation material that conforms to most spaces without disturbing the structure or finish.

Cellulose is one of the earlier insulations but didn’t become a popular choice until the 1950s when fire retardant was added to the material.

What is Cellulose Insulation Made of?

Modern cellulose insulation is made from either 75 to 85 percent ground-up recycled paper or recycled denim.

It is heavily treated – around 15 percent by volume – with boric acid, borax, or ammonium sulfate. While these chemicals aren’t known to be hazardous to people, they can be effective flame retardants and help reduce pest issues.

Wet-applied cellulose has water added during the installation process.

How Cellulose Insulation Works

Cellulose insulation can be used in both existing homes and new construction.

It can be blown as loose-fill insulation in attic cavities, dense packed into walls and floors, or wet spray for new construction that helps increase heat retention and has the potential to dampen noise levels, according to the Energy Audit Blog.

Dense pack cellulose is used more commonly today for adding retrofit insulation. The dense packing into the wall cavities adds a thermal insulation while providing some level of soundproofing.

Wet-applied spray cellulose has water added to it during the application process. The material has the same thermal and sound retardant properties as dense packing, according to the Energy Audit Blog. Wet spray cellulose is almost always installed in new construction before the drywall is put up.

What is Cellulose Insulation R-Value?

R-Value is the capacity of an insulating material’s resistance to heat flow.

Basically, that means the higher the R-Value, the greater the insulating power of the material. The R-Value for loose-fill cellulose is between an R-3.1 and R-3.8 per inch. There is a range here because that number can vary depending on the manufacturer.

The amount in inches of cellulose needed will vary depending on the climate zone where you live.

Now, reducing insulation to a number doesn’t tell the whole story, since heat flows in and out through radiation and convection. Heat loss through convection, or airflow, can account for nearly 40 percent of total energy loss in the home. This is an issue if you are only using R-Value to choose your insulation.

Cellulose Insulation Pros and Cons

All insulation materials have a number of good things and bad things about them.

Let’s dive into the pros and cons of cellulose insulation.

Cellulose Insulation Pros

• Cellulose has more recycled material than any other commercially available insulation.
• Cellulose doesn’t use any greenhouse gases as propellants.
• When blown into stud cavities, cellulose gets into most of the nooks and crannies.
• Cellulose insulation is very inexpensive.
• Boric acid, borax, or aluminum sulfate used in cellulose insulation provide resistance to mold, pests, and fire.
• A machine can be rented at most local home improvement stores to blow cellulose insulation into an attic, making it a weekend DIY project for the experienced homeowner.

Cellulose Insulation Cons

• During the early 1970s retrofits, loose-fill cellulose was used for filling empty wall cavities. Due to blower machine limitations, the material compressed and settled, leaving wide gaps in the wall cavities.
• Modern cellulose settles up to 20 percent, which is problematic in relation to closed cavities causing the home to be uncomfortable and energy bills to rise, according to House Energy.
• Cellulose must be kept dry as it absorbs up to 130 percent water by weight.
• It dries very slowly after absorbing water, causing it to deteriorate and settle afterward.
• After cellulose insulation absorbs water, the chemical fire treatment is destroyed.
• Dense packed cellulose gets everywhere, spilling into the house through any openings in the wall cavity.
• Homes with furnace duct systems can expect some of the cellulose dust to be recirculated through the house.
• Cellulose weighs several times as much as fiberglass, which isn’t an issue unless insulating an attic slope.

Process of Installing Cellulose Insulation

Cellulose insulation can be installed by one of two techniques.

It can be blown-in – loose-fill or dense packed. It can also be spray applied with moisture added.

The dry blown insulation can be installed using a machine to blow the cellulose into the area to be insulated.

In existing homes, installers will remove a strip of exterior siding around waist high. They will then drill a row of three-inch holes – one into each stud cavity. A special filler tube is then inserted, and the insulation is blown-in filling the cavity. When the installation is completed, the holes are sealed with a plug, and the siding is replaced.

For new construction, cellulose can be either damp-sprayed or installed dry behind netting, according to the U.S. Department of Energy.

When cellulose is damp sprayed, a small amount of moisture is added at the spray nozzle tip, adding natural starches in the material, causing it to adhere to the cavity.

How Does Cellulose Insulation Affect Energy Cost?

Heating and cooling a house accounts for 50 to 70 percent of the energy used in the average American home.

Traditional forms of insulation – like cellulose – is resistant to heat transfer, but tends to poorly protect against airflow. This will contribute to the discomfort in the home, as well as energy loss.

That airflow into and out of the home will also cause your furnace and air conditioner to run constantly as those mechanicals try to maintain a constant temperature.

Choosing the Best Insulation for Your Project

You now have a good understanding about cellulose insulation and whether it will meet your expectations for energy efficiency and the comfort in your home.

With that knowledge, you might want to learn more about other insulation materials that may better fit your needs, or you may also just want to keep your options open.

While foam insulation is all we do, the Learning Center on our website has a lot of great resources to help you on your home insulation journey.

Related Articles

About Amanda Ringler

Amanda previously has worked as a breaking news and crime reporter, TV news producer, and editor in Flint and Detroit. Throughout her career as a journalist, she has won several awards from The Society of Professional Journalists – Detroit Chapter and the Michigan Press Association. As part of the RetroFoam of Michigan family, Amanda uses her experience as a journalist to write content that will help educate homeowners on the benefits of foam insulation. When Amanda isn’t writing, she’s spending time with her husband and rescued huskies. She also loves knitting, making art, cooking, and hosting dinner and a movie night for friends and family.

What You Should Know About Blow-In Cellulose Insulation

Lee has over two decades of hands-on experience remodeling, fixing, and improving homes, and has been providing home improvement advice for over 13 years.

Kelly Bacon is a licensed general contractor with over 40 years of experience in construction, home building and remodeling, and commercial building. He is a member of The Spruce Home Improvement Review Board.

Elizabeth MacLennan is a fact checker and editor with a background in earth sciences and sustainability. Elizabeth holds an M.S. from The University of Tennessee, Knoxville.

When you install insulation in an existing closed wall or in an attic, it likely will be a loose-fill product called blow-in cellulose insulation. With an attic, this type of insulation is just one option along with the other popular alternatives, fiberglass batts or blown-in fiberglass. But with enclosed walls, blowing in loose-fill cellulose insulation is still by far the most practical and cost-effective method.

What Is Blow-In Cellulose Insulation?

Cellulose insulation is a type of wood- or paper-based product. It is mechanically blown into or onto empty spaces in the structural part of a house to slow down the transmission of heat or cold.

What Is Loose-Fill Cellulose Insulation?

Cellulose insulation is thick, dense, and clumpy, with a consistency much like down feathers. The chief value of this shape and size is that the insulation can fit in enclosed areas (such as walls) and can conform around obstructions such as wires and ducts (found both in walls and in attics).

Cellulose insulation technically can come from any cellular plant source, such as corncobs or sisal. But commercial cellulose insulations are generally derived from wood, and more specifically from paper: recycled newspapers, cardboard, office paper, and other common waste paper products. For this reason, cellulose insulation is considered an eco-friendly home product.

How Cellulose Insulation Is Blown Into the Home

The most common type that homeowners will encounter is called loose-fill cellulose insulation. This is slightly different from another type of cellulose insulation, which is designed to be blown onto open walls, much like spray foam. In this second type, moisture introduced into the spray helps the cellulose stick to the wall. With loose-fill insulation, however, the cellulose is dry.

To fill finished walls, holes are drilled in the plaster or drywall to permit access of the blower nozzle. For attics, cellulose insulation is blown in parallel to the joists. It can be used by itself to fill in joist cavities that have no insulation or laid as a thick layer over the top of existing batts of fiberglass insulation.

The installation process for dry cellulose insulation looks like this:

1. Densely packed bales of cellulose are fed into the hopper of an insulation blower powered by an electric motor. Rotating teeth or prongs at the bottom of the hopper fluff up the cellulose.
2. The cellulose is blown into the attic or walls through long, flexible tubes that run from the blower to an application nozzle.
3. The cellulose is allowed to fill the cavities or blanket existing insulation. No pressure is placed on the cellulose; it is allowed to settle over time.
4. Walls are patched up and painted over.

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Cellulose Insulation Advantages

There are a number of advantages to using cellulose insulation over other types:

• Loose-fill cellulose insulation can settle around and conform to most of the obstructions found in walls and attics.
• Loose-fill cellulose is relatively inexpensive, yet still has an R-value of about 3.5 per inch of thickness, compared to fiberglass’ R-value between 2.2 to 2.7 per inch.
• When walls are already finished, injecting loose-fill cellulose insulation is one of the few ways of adding insulation. One alternative is to pull down the drywall and use fiberglass batts.
• Cellulose insulation stands up reasonably well against insects and vermin because it is treated with borates.

Cellulose Insulation Drawbacks

There are also a few drawbacks to cellulose insulation:

• While settling is one of blown-in cellulose insulation’s advantages, this can also be a problem, mostly with walls. Over time, the insulation can pack down and form pockets above the settled areas. These pockets become thermal bridges, which transmit heat or cold into the house. Settling in attics is less problematic for two reasons. First, attic spaces can be overfilled to account for settling. Second, when cellulose insulation in attics settles, no empty spaces are formed.
• When cellulose soaks up moisture in enclosed areas, it can take a long time to dry out. Moisture dramatically cuts R-value and may lead to the formation of mold and mildew. Rigid or sprayed-in foam stands up better against moisture.

Is Cellulose Insulation Considered Green?

With cellulose, eco-friendliness is a debatable issue. On the one hand, it can be considered green because it uses up to 85 percent recycled materials. However, the remaining 15 percent, which includes the borate treatment, is less-than-green because it is a chemical treatment.

Fiberglass insulation may use recycled materials, as well. Owens-Corning, one of the biggest names in fiberglass insulation production, reports that it uses between 53 and 73 percent post-consumer recycled materials. So the green advantage of cellulose insulation may be less significant than it is sometimes portrayed.

Cellulose Insulation vs. Other Types

With closed walls, you have few other choices but to blow in insulation. Unless your home is going through some remodeling where the walls are being opened up, holes need to be bored into the walls and insulation injected. Here, the traditional favorite is blow-in cellulose insulation, although spray-in foam is becoming steadily more common.

Tip

Spray-in foam can have an R-value of up to 7 per inch of thickness, giving older homes a better R-value (or better insulation), which helps with heat and cold retention in various seasons.

With open walls, you can install fiberglass roll insulation, although spray-applied foam insulation is also possible.

For attics, the joists are often open and accessible and thus could be insulated with either blow-in cellulose or fiberglass batts. However, because of obstructions such as wires (and just because of its sheer ease), cellulose insulation is often blown into attics, as well.

Is Blown Cellulose Insulation a Fire Hazard?

Cellulose insulation’s source paper in its raw state is combustible. However, during manufacturing, cellulose insulation is treated with borates, which are Class I fire retardants. Class I refers to ordinary combustibles such as wood and paper, as opposed to Class II combustibles, such as flammable liquids, grease, gasoline, oil, etc.

As a demonstration of cellulose insulation’s fire-retarding capacity, it is possible to use a blowtorch to warp a penny resting on a bed of cellulose insulation held in your hand. Not only does the cellulose remain unaffected even while the penny begins to melt, but the insulating value of the cellulose is such that no heat is felt by the hand holding the experiment.