The Truth about Insulation: How it is Installed is More Important than What Kind Is Installed

“I’ve read and heard so many conflicting things about all of the different types of insulation available today that to be honest, I’m more confused now than I was when I started my research.” This is a comment that in one form or another, often comes up when I’m sitting down with a new client, their architect and builder to plan a new green home project. I usually chuckle a bit when I hear this comment because I can fully identify with their internet-induced confusion.

The product manufacturers’ of course present a selective set of “truths” about their product as well as throwing a few hand grenades often labeled as “facts” toward the foxholes of the competition. Of course, all of the competitors are doing the same thing from their side of the insulation wars. The result is that the water is thoroughly muddied and a poor consumer who isn’t a geek about heat transfer physics and building science hasn’t the knowledge needed to sift through all the rubble to uncover the real gems.

I’ll try to help you out. First, you need to know that I don’t receive any money from any insulation manufacturer to promote their product. Second, I have a definite preference for insulations that promote healthy indoor air quality in the home. I hope that you share my concern in this regard. There are plenty of safe, healthy and highly effective options so why put your own or your family’s health at risk? Third, I have a preference for products that have as few barriers to a top quality installation as possible. A great product that is very hard to install well, is not going to make my list of recommended insulations. High quality construction is difficult enough to do well, we don’t need to make it harder on the crews and contractors than necessary by selecting products that require highly skilled and patient artisans to install.

They Can All Work, But...

Next, you should understand that we know a tremendous amount about how insulations work. The good news is that all of the major types of insulations used today will work well, if installed correctly. Insulation can be fiberglass batts, rock wool batts, batts made of old blue jeans, loose blown fiberglass, blown cellulose, or blown rock wool, blown-in-blanket applications of lose fill insulations, spray in place open or closed cell foam, and rigid foam boards to name but a few. In every case, the quality of the installation is of paramount importance. I emphasize the installation of the insulation product as a distinct category because it turns out that our building science research has shown that how insulation is installed is actually more important than which type of insulation is installed. Errors so seemingly small that a typical observer will overlook them will cause the insulation to lose half or more of its ability to stop heat and cold! So what constitutes correct and effective installation when it comes to insulations?

Here is What is Important About the Installation...

I don’t much care which one of the healthy insulation choices you make. I only care that your insulation installation works and delivers the comfort and efficiency you want and deserve.

No matter what type of insulation you select, if it is to deliver the best possible performance it must meet a few basic criteria.

1. The Insulation Must be in Contact with an Air Barrier or it Must be an Air Barrier Itself.

  1.     In order to work well all insulation installations must include an air barrier to stop the flow of hot and cold air.
  2.     This means that either the insulation is an air barrier itself (foam) or it must be installed in continuous contact with an air barrier such as the drywall or sub-floor for example.
  3.     The one exception to this requirement are foam based insulations which are in and of themselves air barriers, too.
  4.     On the other hand, low density insulations like fiberglass batts or loose fill fiberglass or cellulose are absolutely not air barriers! If your contractor stuffs a wad of fiberglass into a hole or lays a batt over a hole and tells you he it will work as an air barrier, fire him and hire someone who knows what they are doing.
  5.     The reason for this requirement is simple to picture. If you insulate the walls of a home with good insulation and close the window to your room, the insulation can work. The heat flow has no choice but to fight its way through the insulation to get through the wall. But, if you open the window, now the outside temperature will not have to work its way through the insulation layer in your outside wall. Instead, the heat or cold simply goes through the window and bypasses the insulation boundary. Your room is soon at the same temperature as the outside. You might as well not insulate if you don’t intend to take the steps necessary to have it in contact with an effective air barrier. The take away is that if outside air can bypass your insulation, you won’t get the comfort and efficiency you want.

Proper installation of insulation

The photo on the left shows us what a good installation of a batt type product should look like.  There are no voids, gaps or compression and the batt is touching the both studs and the top and bottom plate fully. When the drywall air barrier goes up the front of the batts will be in contact with the back of the drywall/air barrier, which is a good thing.  In the middle is what we see nine times out of ten.  The overall R-value of this wall is less than half of what the owners are paying for and think they are getting.  On the right we see batt insulation pretending to be an air barrier.  I have been known to comment that insulation is made in pretty colors so that it looks good even when doing nothing! 

2. No Gaps or Voids Will be Tolerated.

  1.     Voids and gaps are so common in insulation installations that it often looks like the crew installed the product in the dark with no idea how it looked.
  2.     The insulation is not smooth, evenly distributed and it does not totally fill the cavity.
  3.     A study by the Oak Ridge National Laboratory of the U.S. Department of Energy found that a gap of 1/8 between the insulation and the surface of the air barrier  due to stapling the tab on the batts to the inside edge of the studs (wall, floor or ceiling drywall for example) results in a significant 42% reduction in the effective R-value. This means that the R-19 insulation you paid for will function at an effective R-11 with a few small gaps! Your 2x6 wall now delivers less performance than a well insulated 2x4 wall will. (Energy Design Update, Vol. 19. No. 9, September 1999)
  4.     The comfort and energy penalties for sloppy installations are so prevalent that the Home Energy Rating System (HERS) guidelines and the Energy Star for Homes ( program require that the R-value of the assembly cannot be determined until the quality of the installation is inspected to ensure the following requirements are met:
  1.     Quality of Installation - Grade 1-Meets Mfr. Specs./Grade 2-Allows for up to 2% of the area to be missing or 10% compressed-not aligned-gaps but is OK if it has a layer of continuous R-3 or better exterior rigid foam board/Grade 3-2%-5% missing, gaps, voids, insulation or over 10% compressed
  2.     Fully Aligned Air Barriers - Insulation in contact with the air barrier, floor insulation installed pushed up into the floor cavity such that it is in full contact with the sub-floor at all times
  3.     Reduced Thermal Bridging - Use of continuous rigid foam board insulation, insulated headers, band/rim joists, advanced framing
  4.  -If the energy raters and the US Dept. of Energy think that meeting these criteria is so very critical, don't you think your home should meet these industry standards, too?

3. No Compression Will Be Tolerated.

  1.     When insulation is compressed, its R-value is reduced.
  2.     The product has been pushed too far into the cavity, or compressed under a pipe or behind a wire rather than being split and installed on both sides of the obstruction.
  3.     The rate of reduction in R-value is close to a linear match to the amount of compression.
  4.     When six inches of insulation is compressed behind a wire, pipe or other obstruction, that area is rendered almost useless from an insulation performance perspective.
  5.     Again, this is such a common problem that the HERS rating system guidelines require that the R-value of the assembly must be de-rated if even a couple of percentage points of the area suffers from anyone of these errors.

4. No Misalignment With the Air Barrier Will Be Tolerated.

  1.     Earlier I spoke of the negative impact of small gaps and voids in the insulation layer of your home.
  2.     Misalignment denote places where the gaps and voids between insulation and air barrier become dominant and whole areas are effectively uninsulated.
  3.     It is common for me to find batt type insulations lying on the attic floor apparently in contact with the drywall/plaster of the ceiling. But, when I lift the batt up, I often find that the insulation was not in fact touching the ceiling. It was lying on top of wires, pipes, bridging a dropped soffit or just stuffed between the framing members in such a way that it is not aligned well with the air barrier.
  4.     Again, this is such an R-value killer that it home energy raters are required to reduce the average effective R-value of the whole wall or ceiling assembly in their report.

This photo illustrates several insulation errors. At first glance, the floor of this attic looks like it is fully and well insulated, but in fact this is all just a waste of money. The batts are installed floating above the actual ceiling drywall below. This initial installation did no good so the homeowner came back and blew in lose insulation over the top of that, but doing a job wrong twice rarely fixes the problem. The home still wasn’t comfortable because there is no insulation in contact with the air barrier of the room below so nothing is working as it was intended.

5. No Thermal Bypasses

  1.     Thermal bypasses are places where insulation is replaced by materials that allow a fast track for heat to flow into or out of your home.
  2.     Some of the largest and most critical thermal bypasses are formed when during framing lots of wood is bunched together on the exterior of the home and it is not covered with any type of insulation.
  3. Wood has an R-value of about 0.8 per inch of thickness so a 2x4 edge on is only about R-3! 
  4.     This usually happens at corners, windows and doors.
  5.     While wood framing results in a thermal bypass (short circuit) in the insulation protection of a home, to really make the insulation placed between the studs a complete loss, replace the wood studs with metal studs.
  6.     Metal studs allow 400% more heat flow than wood studs.

This is an exterior IR photo (shows heat) of a home with metal framing members from the outside on a winter day. The spaces between the metal studs are insulated with a spray in place half-pound foam that was well installed. The red-hot glowing vertical lines you see are due to the extreme heat loss through the metal studs. What went wrong you ask? The builder failed to install a rigid foam board insulating sheathing over the exterior of the studs. He forgot to put the cozie on his metal house. I was there on a forensic inspection because after spending a year in their supposedly green and efficient retirement home, it became clear that in fact their new home was miserably uncomfortable and expensive to operate, too.

Above left you see a beautiful installation of batt type insulation with a vapor retarder backing. On the right side above you see an equally well done installation of unfaced batts. ( Note that when the drywall is installed, it will be in full contact with the insulation and there are few if any gaps, voids or areas compressed below the level of the stud face. Yes, it can be done, but in the real world out in the field, it almost never is. Why? Well, the insulation crews are paid by the job so the faster they install the product and move on to another job, the more they make. If you want them to slow down and do the work like what is pictured above, then you will need to find a contractor who is willing to pay for the added labor and training to create a crew that can deliver work like this. The problem is that once you pay that added amount for high quality labor and the extra time, fiberglass has lost its price advantage.  My advice is to install one of the total wall fill insulations and gotten a better job for virtually the same dollars paid.

Here we see two ways to install a blown in blanket of total wall fill insulation. A fabric blanket is installed across the studs and then insulation is packed in behind the fabric using a high pressure hose to blow it in. The photo on the left is a blown in blanket of lose fiberglass. Note the access holes for the high pressure hose in the fabric that contains the insulation. The key rule of thumb here is to be sure that your blanket is densely installed! I see crews trying to get by with installations so sloppy and loose that I can easily compress it by one-quarter of the full depth! The insulation is far from the 3.5 pounds per cubic foot density that one needs to see according to industry standards to function as an air barrier. On the right, you can see a blown in cellulose blanket. The fabric blanket has been pulled off the stud on the lower left to show how a densely installed insulation should be so packed into the wall that it doesn’t fall out when the fabric layer is removed! Also look at how the insulation has flowed and conformed to every odd shape and nook in the framing and wiring.

The Basic Choices Are...


Here we can see how one of my personal favorites (hey, it’s my blog, I can endorse it if I want to) types of insulation, cellulose. In this case, it is a damp spray application. First, it is sprayed in place with a safe water activated natural glue. Then it is shaved level with the face of the studs as you see in the photo on the right, leaving a dense total wall fill insulation. Cellulose insulation is where most of your recycled newspapers end up. They are ground up, treated with a borate derivative that makes it fireproof, mold resistant and intolerable for bugs to live in, too! There are also cellulose insulations that use other compounds, but I don’t care for them and always insist on the wet treated borate type. The damp treated process soaks the cellulose fibers in a solution of borates so that the fire and bug proofing is absorbed into the fibers and not just a powder dusted on the product. (


Here we have the last and newest type of insulation, spray in place foam. These foams come in two basic types, open and closed cell. This is simple. If you live in the Climate Zone Five or higher you should only use closed cell foam. Closed cell foam is a vapor barrier and in the frozen north this is required to avoid moisture damage due to condensation. In the majority of the country (CZ4 and lower) you can use either open of closed cell. Most installations are open cell because it is less expensive by a good bit. On a technical note, it is also vapor permeable and that is a good thing if you live where the summers are humid and you never get Canadian coins as change. The photo on the left is open cell (0.5 pound per cubic foot density) and the blue foam on the left is closed cell (2.0 pound per cubic foot density) foam. I will say that closed cell foam is a good option in another niche climate, the beach. Closed cell foam can add rigidity to the framing of a home and it has been shown to improve the amount of wind a roof can withstand during a hurricane by (


The insulations that are widely used today are all tested and code labeled as meeting the requirements of the energy (IECC) code. Insulation is a very fussy and finicky product to install correctly so that it can work effectively. It can lose much of its effectiveness if it is installed with any gaps, voids, compression or if heaven forbid there is no well sealed air barrier in contact with it! This means that in the final analysis the guy(s) who actually do the installation are more critical than the product selection you make. (In this way it is just like air conditioning/heating systems.  The design and installation are far more important there too than equipment brand names.)  You can help yourself out by selecting an insulation type that makes it easy for people who are often poorly trained, poorly paid and in a big hurry to do the job right. This means picking an total wall fill system like foam, blown in blanket or damp spray applications of cellulose, fiberglass or rock wool. If you choose a batt type of any kind know that since few things in home construction are square, plumb and spaced out perfectly, the crew will often be trying to fit a square peg into a round hole while working behind a 12 gauge wire and a drain pipe. I’ve shown you photos that prove any of these products can be done and done well. But that is only the first chapter of the whole story of comfort and efficiency in your home.  Picking the right product makes a happy outcome far more likely and isn't that what you really want?

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