Which Is The Best Winter Attic Insulation: Loose Fill Fiberglass Or Cellulose Insulation?

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Are you wondering how much it costs to install cellulose attic insulation?

October will be here in a handful of days, football season is already on us, and winter’s damp cold temperatures are headed to Atlanta!

Cold temperatures bring aching joints, runny noses, and bigger loads of laundry because of the heavier clothing. Are you ready for winter?

And, with fewer hours of sunshine, the free radiant heat from the sun will be sparse.


Vented Attics are not your friend in winter

“So Bob, where does most of the heat escape from my house?”

The answer is easy: your vented attic. Your vented attic is the biggest source of heat loss in the average Atlanta home. And therefore, upgrading attic insulation usually is the energy saving investment with the quickest payback (ROI), and brings dramatic improvements in comfort.

What can you do to improve the thermal boundary between your heated indoor space, and the vented attic space?

The best thing you can do is load the attic floor with fresh insulation!

What kind of insulation, and how much?

The two most popular types of attic insulation in our region of the country are loose fill fiberglass, and loose fill cellulose insulation.

Both types of insulation will improve the thermal boundary between your ceiling and the frigid & damp attic. How they do it is two different ways. It’s like gas and diesel powered vehicles – both are vehicles but they get you down the road by different means.


Loose Fill Fiberglass Attic Insulation

Fiberglass insulation that is blown out of a hose is referred to as loose-fill insulation. This type of insulation is made up of zillions of tiny glass strands. Each strand has jagged edges that cause them to “lock” together as they fall and land on the surface, i.e. your attic floor.

Loose fill fiberglass insulation earns it’s R Value by trapping airflow. In other words, it has zillions and zillions of microscopic air pockets created by those glass fibers, and those pockets slow down the movement of airflow traveling through the insulation

How Does Heat Move?

If we want to slow down the flow of heat in our attics, we need to know how it’s sneaking in, and how it’s sneaking out, right?

Heat that is transferred by air currents is called convective heat loss, (or convective heat gain, as in the summer).

However, heat moves in three forms, not just one.

The other two forms of heat transfer are:

1. Conduction: When heat is transferred by one surface touching another surface. (Think of your bottom sitting on a cold bleacher for a November Friday night football game).

2. Radiant: This is how heat travels from the sun to earth; electromagnetic waves. Your car seats and dash get scorching hot in a summer parking lot, because of radiant heat.

Here in our Atlanta & North Georgia market, the county codes restrict builders to a minimum of R-38 attic insulation before they can sell the house

The U.S. Department of Energy recommends R-49 for these same attics.

So you have your minimum standard (R-38) and you have the recommended level, R-49 for attic insulation.

And, these two standards are what we use as guidelines when advising homeowners who are upgrading your existing attic insulation.

R Value Isn’t the Whole Story

However, R Value is tested by measuring Conductive heat loss, only. R Value does not address radiant heat nor conductive heat.

Do you recall the last time you held a cup of coffee in a glass coffee cup? We all know that glass is a poor insulator of heat. But glass in the form of short, jagged fibers piled up on top of one another begins to trap air, and insulate against the movement of heat that moves by contact (conductive heat).

Remember a sunny day when you parked in an open parking lot, and your dash and seats were warmed by the sun? That windshield is glass. And glass (unprotected by UV blockers) freely allows the electromagnetic wavelengths (radiant energy) of the sun to pass. As those waves pass through the roof and pass into loose-fill fiberglass insulation, the glass & air does a very poor job of resisting the wavelength. In winter, these wavelengths of heat pass through the sheetrock ceiling, only to easily escape to your vented attic.

As for convective heat movement, loose-fill fiberglass struggles. It is a low density insulation. At lower installation levels it allows air to virtually freely move through the fibers.

If you are choosing loose-fill fiberglass attic insulation for your home, I’d only consider it under two conditions:

– Thoroughly air seal the attic floor.

– Install R-60… simply because it allows so much air to freely move through the insulation. It needs to be piled high, really high!

So loose-fill fiberglass, in my book, is not the better retrofit insulation material for attics in my market. It works, but cellulose works a little bit better.


Cellulose Attic Insulation

Because cellulose is recycled wood pulp (paper products) it is considered a high density insulation material. Like fiberglass loose fill insulation, cellulose insulation is also installed from a hose, being blown into the attic and settling on the attic floor.

But that is the ONLY similarity between the two products. Like gas and diesel, they are completely different materials.

Cellulose earns its R Value by blocking air flow. It cannot be fluffed or injected with excess air, like some loose fill fiberglass products. Fluffed fiberglass insulation will measure high on the rulers (“We’ve installed 24” insulation in your attic today!”). However, because it was injected with excess air, it readily settles and homeowners who pay attention to these things easily see the 24” may now only be 20”.

In all three categories of heat transfer, cellulose out performs loose-fill fiberglass insulation, in my opinion.

This is why we can add a few inches of cellulose insulation on top of an old layer of poorly performing fiberglass insulation, and our homeowners become raving fans for cellulose insulation! The benefits are noticed immediately.

Benefits of cellulose attic insulation

Literally, the benefits of cellulose attic insulation for existing attics are obvious:

  1. When a few inches of cellulose insulation are installed on top of fiberglass insulation, it dramatically slows the convection. You benefit! Would you rather use a crocheted afghan blanket or wool blanket to keep warm while sitting on those outdoor bleachers? Cellulose insulation is comparable to the effect of the wool blanket.

2. Due to the mass, a few inches of cellulose insulation absorbs the wavelengths of radiant energy. You benefit! I’ve often said, “Hire me to install a few inches of cellulose insulation in your attic, and I’ll give you the radiant barrier for FREE!”

3. Cellulose (wood) is a better insulator than glass, when it comes to conductive heat gain and loss. You benefit!

Why don’t more companies install cellulose insulation? I can only guess. But here is what I’ve learned in over 20 years in my market, as a cellulose contractor who works only for homeowners in existing houses.


Three Reasons the “Other Guys” Don’t Want to Install Cellulose Attic Insulation

  1. Cellulose takes more material to insulate the same attic space, vs loose-fill fiberglass. Therefore, cellulose requires more space in the truck or trailer, and takes more time to install.

2. Cellulose attic insulation should be installed using a water sleeve (internal misting system). This is extra equipment, and has to be monitored. Whereas, loose-fill fiberglass is simply dumped into the hopper and blown out a hose.

3. When a fiberglass crew is forced to install cellulose attic insulation, without a water sleeve and pump, and without much cellulose experience, they will invariably howl and complain loudly, because of the dust. And, the homeowner will be prone to complain too. I don’t blame them! (It’s these experiences that give rise to the rumor that cellulose is dusty). Installed correctly with a trained crew, cellulose is a beautiful thing, baby!

This winter, I am asking you to consider cellulose insulation for your attic upgrade.

But do yourself a favor: ONLY ask for cellulose if it will be installed with a trained, experienced crew using the proper equipment.

Specifically, our company installs all-borate cellulose insulation. We believe it’s the finest product for loose-fill insulation. And so far, several hundred homeowners each year … for 20+ years – are raving fans and agree, Cellulose insulation is your best choice for winter insulation to protect your ceilings!

– Bob Bird

Bird Family Insulation


Want to hear more information on why we love cellulose so much? Check out this video! https://www.youtube.com/watch?v=PC3aq3P9sUY

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