How Does Insulation Work?

How Insulation Works

Insulation is a thermally resistant barrier which inhibits the migration of thermal energy into and out of the house. In simple terms: insulation blocks heat from entering the home in the summer and holds heat in during the winter. The results are a cooler home in the summer, warmer home in the winter, and lower energy bills. It’s that simple and it really works. Insulation is so effective that its cost is often paid for through energy savings in less than a year…and with the rising cost of natural gas and electricity, savings may come even sooner!

Where insulation is installed

During the summer the suns powerful rays radiate down onto our homes, the roof and walls heat up and the temperature in the attic can rise to nearly 170 degrees. This heat enters the home and causes things to become quite warm and uncomfortable. You then have two choices….turn on the air conditioning and watch the electric meter spin, or suffer with the heat.

Homeowners often complain of an air conditioning system that runs all day and never cools the house below 80 degrees. This is typical of a poorly insulated home, the heat is entering the home at about the same rate as your air conditioning can cool it. The solution is to reduce the heat-load and block the heat from coming into your home. Insulation installed in your attic and walls will dramatically reduce the amount of heat entering your home; the house stays cooler longer into the day and the air conditioning, when it does come on, runs much less often. When we insulate homes during hot days, customers often notice an immediate difference and frequently describe the feeling as though a huge shady cloud came over their home.


Insulation makes a huge difference in the winter, it’s amazingly effective when it comes to retaining heat. Just as insulation can block heat from entering the home in the summer, it too works in the same way to keep the heat contained within the home during the winter. Homeowners frequently complain of cold homes and furnaces that run continuously. This is because the heat is escaping about as fast as the furnace can produce heat. Once insulated, heat is retained within the home for hours longer. The result is a warmer home that uses much less energy to stay warm.

Why insulation goes on the floor of the attic and not on the underside of the roof:

Attic insulation should be installed directly on the floor of the attic, which is your ceiling and this is because you are heating and cooling the area below the ceiling, this is referred to as conditioned area while the area in the attic itself is considered unconditioned area.

In the winter you want to retain the heat in the home where you live, you don’t want heat to rise through the ceiling. If you were to put insulation under the roof, then heat would wastefully rise into your attic area where it would be readily lost through attic ventilation. During the summer it would seem like a good idea to also insulate the underside of the roof in an effort to keep the attic cooler, but the roof rafters are limited in being able to hold either R13 or R19 rolled fiberglass, which is not enough to entirely block the heat from coming into the attic; by the afternoon the attic will get quite warm/hot and then the insulation installed on the roof rafters will serve to hold that heat in over night and the attic insulation on your ceiling won’t be able to cool down over night. Also, your roofing material will get hotter because the heat won’t be able to ventilate underneath, most roofing warranties are void unless you have adequate attic ventilation.

Our feeling is that a very well insulated attic (insulation installed on the floor of the attic against the ceiling), brought up to R38, should sufficiently work to keep the inside of the home comfortable in both summer and winter. To further help in the summer you could install additional attic ventilation to allow heat to escape and keep the attic cooler. For homeowners who really want some form of additional insulation under their roofing, we can install radiant barrier which will help reflect/refract heat energy and serve to keep the attic cooler in the summer and even retain more heat in the winter.

Additional benefits of Insulation

A well insulated home means the air conditioning and furnace system work less often, besides saving money on heating and cooling bills, the air inside the house does not get processed and cycled as much through your HVAC system, which means the air does not get nearly as dried out.

Insulation also serves to reduce outside sound from entering the home. People near airports and schools often report dramatically less sound infiltrating and most people describe the home as having a more solid feeling to it.

The non-flammable nature of cellulose insulation offers a degree of fire protection to the home. The insulation becomes a “hard-target” that the fire has to burn around, thus slowing the spread of fire by 57%. In testing, a well insulated home remained structurally intact and standing significantly longer then a non-insulated or fiberglass insulated home.

Also, because cellulose is treated with borate, the material is resistant to insect, termite, rodent, vermin, mold, mildew and fungus. There’s even a reduction in condensation on ceilings and walls.

Blown vs. Rolled (Batting)

Fiberglass rolls (or batts) are useful in that they can be hung under floors or used in open-framing and in new construction situations. But once a home is built it can either be rolled with batting OR blown with a loose-fill (fiberglass or cellulose) material. A blown application offers several advantages over batting.

Many homeowners assume batting is better, or they’re drawn to what appears to be a cleaner job. Some homeowners are directed by their trusty contractor while others just feel a sense a familiarity towards the rolls. The truth of the matter is that rolled fiberglass is often installed during construction merely because it’s convenient. When homeowners, contractors or architects do some research, cellulose blown insulation easily emerges as the best choice.

The downfall of rolled material is that it must be placed between each ceiling joist, sometimes fitting tightly, sometimes loosely. Rolled material must go over, under and around the many obstacles in the attic such as plumbing, piping and electrical conduit; this application compromises the performance of the insulation by creating gaps, voids and other “leaks”. The blown application seals and provides a much “tighter” blanket of insulation throughout the attic, this is referred to as a “monolithic fill”, which is a fancy way of saying that the blown material and application offers a continuous blanket of insulation that covers and seals over everything as a solid blanket.

Studies at the University of Colorado have established that a blown-in insulation rated at R-19 provides equal performance to the same job done with R-30 batting. The flip side of this equation is that R-30 batting only renders an R19 in practical effectiveness. So while the rolled material is rated and stamped as R-30, it’s only offering a real performance of R-19.

Another problem arises when an attic already has an old or existing insulation. Most homes at one point or another were insulated with old insulation; rolled material does not lay well over existing insulation, the result is a lot of voids, gaps and a compromised fit. Because of this, only homes that have no existing insulation are candidates to be rolled with fiberglass. Some people figure they can vacuum-out or remove the old insulation, but this is extremely time-consuming, expensive and impractical, the best thing to do is simply add more material on top of the existing insulation to bring the entire attic up to R-38.

Another advantage of blowing insulation is that we “shoot” the material up to 20-feet in distance, this allows us to reach all the tight areas that would otherwise not be accessible with batting. We also don’t have to work over every square foot of the attic, thusly reducing the potential for disturbing wiring or placing weight over long stretches of ceiling framing that may cause the ceiling to deflect of crack under the weight of the installers. The blown material reaches the deep corners and covers the entire attic floor.

The most important benefit of blowing insulation is that it allows us to use cellulose insulation instead of a fiberglass product. Cellulose is by far a more effective, efficient, longer lasting and safer material as compared to fiberglass. Please see our materials comparison section for more details.

Cellulose vs. Fiberglass Studies by the University of Colordao

In a two-month study at the University of Colorado School of Architecture and Planning, researchers compared the energy conservation efficiency of two test buildings.

In one building cellulose insulation was installed in the attic and walls. In the second building fiberglass was also installed in the attic and walls. Here are the results:

  • Cellulose achieved a tighter building cavity and cut air infiltration by at least 30% more than fiberglass.
  • When the heat was turned off at night, over a 9 hour period, the cellulose insulated building retained 7 degrees more heat than the fiberglass insulated building.
  • It was estimated that in the temperate climates a cellulose insulated building would require about 26% less energy to heat than a fiberglass insulated building. It was further concluded that the energy benefit would become even more significant in severe climates
  • Cellulose blown-in insulation reduces air leakage more effectively than fiberglass batting or fiberglass blown-in insulation.

Conclusion: Homes insulated with cellulose insulation require considerably less energy to heat and cool then homes insulated with fiberglass. Cellulose is the better insulation.

The Wrong Advice

Over the years I’ve had a lot of homeowners tell me “I don’t want that blown stuff”. When I ask why they feel that way, it’s one of either two reasons, but the thing you have to remember is that not all blown insulation is the same!

“My contractor told me to stay away from blown insulation”
For many years blown fiberglass was popularly installed in attics, this material actually clings to your clothing and makes your skin itch for days! Just about any electrician, plumber or contractor who has worked in an attic full of blown fiberglass will preach his words of hate and despise for what he simply refers to as “blown insulation”, but he’s making a big mistake: not all “blown insulation” is made of Fiberglass. Because Fiberglass is made of glass fibers, it itches, but cellulose does not itch in the least, it’s a soft material and is very easy to work with. Once contractors learn the difference between Fiberglass and Cellulose, as well as understand the many benefits of Cellulose, they tend to prefer and strongly recommend it.

“I had blown insulation in my old home and it settled down to I don’t want it again”
Here again Fiberglass is the culprit. Much like the cotton-candy that Fiberglass resembles, blown fiberglass becomes fluffed-up when it’s blown into the attic. Over the course of time, blown fiberglass settles and packs tremendously. To be fair, cellulose insulation can also settle over time, but to a far lesser degree. Today’s cellulose is “stabilized” and actually carries a lifetime guarantee to never settle, pack or lose its insulating qualities. So to address the concern, blown Fiberglass absolutely will settle, but not cellulose. Again, the same mistake of assuming all blown insulation materials are the same.

So why do Insulation companies still use Fiberglass?

1) Most Insulation companies primarily work with new-construction projects that require rolled Fiberglass; the more Fiberglass product they use, the better their purchasing tier and so they tend to promote and use Fiberglass where they can.

2) Blown fiberglass can be “fluffed” and gets amazing coverage, if you can convince customers it’s a good product, it’s much more profitable to work with or you can offer a lower price to get the job.

3) Many companies don’t own the expensive equipment (insulation blowing machine and dedicated truck) to perform the work, so they promote rolled Fiberglass.

4) Most homeowners are very familiar with Fiberglass, they’ve seen it at Home Improvement stores or at new construction sites, so that familiarity lends towards helping sell it.

In all fairness, there are applications where Fiberglass is a prudent choice: under floors where it can be wired in place, on vertical knee-wall sections in an attic or for new-construction and open-framing situations, but with today’s building trends, Cellulose insulation is more often being used because it’s more effective, more efficient, longer-lasting and safer, it’s just a better product.