Blown in insulation, also called loose fill insulation, is made of fluffy fibers of cellulose, fiberglass or mineral wool. It blown into walls, attics and floors with special equipment. One the main advantages of blown in insulation is that it fills in odd-shaped cavities, crevices and gaps and eliminates cold spots. We’ll be talking about each different type of blown in insulation in a minute, but first, let’s go over the pro term for this week.
Pro Term: Convection
Convection is heat flow caused by air currents or circulating air— like in a convection oven. Insulation aims to greatly reduce convection. Convective heat loss in insulation is rare, but it can occur when there are large temperature differences above and below insulation. Listen up in the mini lesson for what type of insulation can have problems with convective heat loss.
Now, let’s start today’s mini lesson by talking about loose fill fiberglass insulation.
LOOSE FILL FIBERGLASS INSULATION
Loose fill fiberglass insulation, like fiberglass blanket insulation, is made predominantly of glass fibers. An insulation blower is used to install the chopped fiberglass into wall and ceiling cavities.
Blown in fiberglass has an R-value ranging between 2.2 and 2.7 per inch.
Pop Quiz: Define R value. R value was our pro term in episode 27 called Insulation 101. R value is the resistance to heat flow. The greater the R value the more a material will resist heat loss and heat gain. And you can increase a wall’s R value by increasing the thickness of the insulation. So with each inch of blown in fiberglass insulation, you’re increasing your R value by 2.2 or more.
Loose fill fiberglass contains 35-60% recycled content, it resists moisture and mildew and, unlike fiberglass batts, it does not contain formaldehyde.
If you think that blown in fiberglass is the right choice for your home, you’ll have to decide between standard blown in insulation and a BIB system, which stands for Blow In Blanket System.
With standard blown in insulation, the loose fibers are simply blown into wall and ceiling cavities and that can leave loose fibers floating in the home… not a good thing since loose fill fiberglass can irritate your skin and lungs just like blanket fiberglass can. The second option, the Blow In Blanket System, is a system that contains the blown in fiberglass insulation with membranes or netting. Not only do these netted cavities help contain the loose fibers, but they also provide increased R value when compared to standard blown in fiberglass.
BIBS have an R-value of 4.2 per inch. This system must be installed by licensed, certified, trained professionals. You can search for certified professionals in your area by going to BIBS.com.
Although you DIYers are not allowed to put in Blow In Blanket Systems, you can install in your own standard blown in fiberglass. That can save you up to 70% of professionally installed blown in insulation. You can rent an insulation blower from local home improvement stores or tool rental stores. But you should definitely consider hiring a professional if your project is complicated or if you aren’t particularly handy.
So far, loose fill fiberglass sounds pretty good, right? But, let me tell you about the main disadvantage. Even if it’s properly installed, blown in fiberglass insulation can lose up to one half its R value at very cold temperatures, especially sub zero temperatures. This is because it’s so lightweight and fluffy that air can easily move into and through blown in fiberglass, causing convective heat loss.
That ability of air to easily move through fiberglass is why air filters are often made of fiberglass. Air movement is good for air filters, but not so good for insulation. You can combat that air flow problem of by topping blown in fiberglass with blanket insulation or a higher-density loose fill insulation, like cellulose.
LOOSE FILL CELLULOSE INSULATION
Loose fill cellulose is effective at all temperatures and has an R value of 3.2-3.8 per inch. Remember that standard loose fill fiberglass insulation has an R value of 2.2-2.7 per inch and a BIB system has an R value of 4.2 per inch. So, the R value of cellulose falls between the two fiberglass options.
Cellulose insulation is the most commonly used blown in insulation material. It is typically comprised of about 85% recycled newspaper or cardboard, plus 15% of a fire retardant. One fire-retardant chemical that is often used is boric acid and it has an additional benefit of repelling pests and rodents. Another advantage to cellulose is that it is a good sound proofing material.
Often, cellulose is damp when installed so it’s important that the wall cavities not be closed until the insulation has dried completely.
In contrast to the fluffy, lightweight nature of loose fill fiberglass, cellulose is heavy— in fact, it’s too heavy for many attic installations. If you want to use it in ceilings, drywall must be at least 5/8 inch thick, instead of the standard half inch thick. And many experts recommend beefier, traditional framing, with studs 16 inches on center, instead of advanced framing with studs every 24 inches. The thicker drywall and extra framing material help to ensure that the ceiling doesn’t sag from the weight of the cellulose.
Cellulose is packed tightly to resist air flow, but over time, it can settle almost 20%, reducing its R value. If an inexperienced, or untrustworthy installer fails install extra product to offset settling, the R-value of the cellulose will be less than it should be. Fiberglass insulation can settle a bit too, but not as much of cellulose. Like fiberglass, cellulose is sometimes installed in combination with a netting or membrane system.
Your insulation subcontractor should follow manufacturer’s instructions, which indicate the amount of material that should be installed for the desired R value. The amount of cellulose is measured by "bag count” per square foot.
The initial thickness that should be installed is always greater than the settled thickness. Product labels provide the initial installed thickness required to achieve the desired settled thickness. If you aren’t going to have a home energy rater inspect the insulation, you might want to perform a bag-count and collect empty bags at the end of an insulation job to make sure that the appropriate amount of insulation has been installed.
Another downside to cellulose is that it is less water resistant than fiberglass or mineral wool. Cellulose dust is another small problem. The dust fibers are too large to lodge in your lungs, so it’s not a health issue, but it is a bit of an annoyance.
LOOSE FILL MINERAL WOOL
Finally, a quick word about loose fill mineral wool. It’s made of fibers of natural rock or minerals. It has an an R value of 3.0-3.3 per inch.
Like fiberglass, it can irritate the lungs and skin. Unlike fiberglass, mineral wool is resistant to airflow. It’s a decent sound proofing material and its non- combustible. It is usually slightly more expensive than fiberglass or cellulose and not used as often. Like cellulose it’s heavy, so thicker drywall and traditional framing are recommended for ceiling installations.
Alright, let’s do a couple of quiz questions.
1. What type of insulation is made from recycled newspaper and cardboard?
The answer is cellulose insulation. It is typically made of about 85% recycled newspaper or cardboard, plus 15% of a fire retardant. Remember that the main disadvantage to cellulose that it can settle over time, so extra cellulose must be initially installed to offset that settling.
2. True or False. Thicker drywall is recommended if you want to install blown in fiberglass in ceilings.
The answer is false. Loose fill fiberglass is lightweight, so thicker drywall in the ceiling is unnecessary. Loose fill cellulose and mineral wool insulation are too heavy for standard half inch drywall on the ceiling. If you want to use cellulose or mineral wool in the ceiling, ceiling drywall should be at least 5/8 of an inch thick and traditional framing, which is beefier, is recommended over advanced framing. This will prevent the ceiling from sagging.
3. What type of blown in insulation can lose up to half its R value in very cold temperatures?
The answer is blown in fiberglass. Because it is lightweight and fluffy, air can easily move through the insulation and cause convective heat loss. Even properly installed blown in fiberglass insulation can lose up to half its R value in very cold temperatures. To combat this problem, you can top blown in fiberglass with blanket insulation or cellulose insulation.
That’s all I have for you this week.
Please remember that the purpose of this podcast is simply to educate and inform. It is not a substitute for professional advice. The information that you hear is based the only on the opinions, research and experiences of my guests and myself. That information might be incomplete and it’s subject to change, so it may not apply to your project. In addition, building codes and requirements vary from region to region, so always consult a professional about specific recommendations for your home.
Thank you for stopping by. I hope you’ll come back next week for the another episode of Build Your House Yourself University (BYHYU).
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