Fiberglass Insulation vs. Cellulose Insulation
In the world of insulation, seldom things are more heatedly debated than which type of insulation is better: fiberglass insulation or cellulose insulation. Both have their strengths and weaknesses, so let's see what all the fuss is about.
In order to fairly compare the two types of insulation, you have to consider all of the qualities the best insulation should do. This includes things like:
Increase the level of energy efficiency of your home
Reduce the risk of fire
Limit the amount of sound that passes through your walls and ceilings.
Increase Energy Efficiency
Increasing Energy Efficiency is such a vague concept. So, let's cut to the chase and just say Energy Efficiency = Lower Utility Bills.
define the overall energy efficiency of your home with the amount you spend each month to keep your home at a comfortable temperature or your heating and cooling bills. After all, isn't that the only thing that really matters?
This is a better criteria to use than simply stating R-values because this is where the real differences between fiberglass and cellulose insulation are obvious.
Although both types of insulation can offer similar r-values per inch, this only measures the insulation's ability to reduce conductive heat transfer. Which only addresses heat passing through home's building envelope if it's undisturbed by air currents.
In reality, the wind blows and heat rises creating convective heat loss. Which is heat carried through the air. Conductive heat loss accounts for a significant amount of energy consumed in the average U.S. home. Warm air currents passing through the walls, floors and ceilings in your home increase the amount of money you spend on energy bills.
Reduced Air Leakage = Increased Energy Efficiency
FIberglass insulation's main drawback is its inability to block air from passing through it. This may not sound like a big deal until you realize that 20%+ of your heat or air conditioning can pass through the fiberglass insulation.
Densely packed cellulose limits air movement and prevents drafts much better than fiberglass insulation. This is well documented by the University of Colorado in their 1990 evaluation of identical homes insulated with fiberglass and cellulose. The results of their study showed cellulose reduced air leakage by 38% and required 26% less money to heat and cool than the fiberglass home.
Fiberglass Insulation and Cellulose Insulation Offer Similar R-Values
Both cellulose and fiberglass insulation provide about the same level of insulating power or r-value per inch with slightly different results based on the installation procedure.
- Fiberglass Batt or Roll Insulation - R3.2
- Fiberglass Insulation Blown-in Attic - R2.2 - R4.3
- Fiberglass Insulation Blown-in Wall - R3.7 - R4.3
- Cellulose Insulation Blown-in Attic - R 3.6- R3.7
- Cellulose Insulation Blown-in Wall - R 3.8 - R3.9
Both fiberglass and cellulose insulation can be installed to completely fill the space inside of wall, floor or ceiling cavity. Properly installed they will both remain in place for the life of the home. So it seems to me, the real debate stems from the reality of installing the insulation.
The Reality of Installing Fiberglass Insulation
Fiberglass insulation gains its insulating power by trapping air inside of the billions of tiny glass fibers. The air trapped inside of the air pockets is what actually slows the transfer of heat through the space.
Trying to create a continuous even layer of tiny air pockets with fiberglass insulation is extremely difficult. Mainly because fiberglass insulation comes in batts or rolls and must be cut to fit exactly into place. Wires, pipes, ducts and the wood framing itself always get in the way. So the person installing the fiberglass insulation is basically assembling a massive jigsaw puzzle where each piece needs to be cut perfectly with a $3 utility knife. To make things even harder, the fiberglass insulation is thick and squooshy. Cutting each piece to fit around all of the obstacles and tuck it neatly into position is slow and tedious.
In real life, there's just no time for this painstakingly slow process. So many fiberglass insulation installers completely disregard the obstacles and jam the insulation into place, hoping that the drywall with cover up their mistakes (which it always does).
Jamming fiberglass insulation into a space compresses the insulation and squeezes out most of the air pockets. Without air pockets to slow down the heat, compressed fiberglass insulation does little more than fill the space with colorful fibers. The homeowner is left with a collection of holes and compressed insulation throughout their home sacrificing R-value, comfort and energy efficiency.
The Reality of Installing Cellulose Insulation
In contrast to fiberglass insulation, cellulose insulation does not trap air in between it's fibers to control heat. By nature, the cells inside the cellulose insulation have their own insulating power. Which means cellulose insulation can be compressed into a space and offer additional r-value.
Cellulose insulation is actually shredded paper with a fire retardant chemical known a borate. During the manufacturing process, this paper is broken down into its most basic element, cellular fibers from a tree. It's these fibers that provide the insulating power for cellulose insulation.
Installing the granular fibers that comprise cellulose insulation is done with a specialized machine known as an insulation blower. During the installation, the cellulose fibers flow through a long hose guided by the insulation contractor where it's blown or sprayed into the space. Controls on the machine allow the installer to select the density of the insulation which enables them to densely pack it into a wall or floor cavity. Dense packing cellulose insulation into a wall or floor creates a continuous even layer of insulation. Pipes, wires, ductwork and electrical outlets are no problem for cellulose insulation because it is blown into the space is tiny pieces that fill in around the obstacles.
The end result is usually much closer to our ideal insulation criteria from above. Cellulose insulation offers a more consistent, worry free installation when performed by a professional. Mainly because it completely fills the space between the framing by easily filling in around all of the obstacles, offers a slightly higher r-value per inch and will remain locked in place from the high pressure installation. Another important benefit from dense packed cellulose is its ability to limit air movement which cuts down on heat loss through convection. Another major weakness of fiberglass insulation which does nothing to stop air from passing through it.
DIY Installation Realities
Despite the challenges, fiberglass insulation can be installed to reach it's full potential. It just takes a little extra time and couple of tips and tricks to maximize the R-value and overcome its inherent drawbacks. If you're planning on installing fiberglass insulation in your home. I'd recommend watching this video I've put together.
A DIY alternative to dense packing cellulose insulation is a loose fill application. Dense packing requires a powerful blowing machine to force the cellulose fibers into position. But blowing cellulose insulation in an attic, known a loose fill, is an easy DIY project that you can do with a buddy in a few hours.
Lowes and The Home Depot sell Green Fiber cellulose insulation that comes in 18 pound bags. They also offer a free rental on the blowing machine if you purchase at least 20 bags.