“Overblows of 25% in Attics are common in the [fiberglass] industry, with some jobs overblown as much as 50%.”(2) -former President of the Insulation Contractors Association of America

“In 79% of the homes we evaluated....the R-value was not achieved.”7 - Douglas S. McCleery, P.E.

Overblowing results when contractors blow in fiberglass to the depth listed on the bag label but cover a larger area than prescribed. The fiberglass is fluffed with too much air. In these instances, the labeled R-value is not achieved because too little fiberglass has been installed.

Put simply, overblowing is under-insulating. The customer doesn’t receive the R-value they paid for.

Common Bird or Rare Species?
Of course, overblowing wouldn’t be too much of a concern - if it was rare. But industry professionals believe that it is not.

“Overblows of 25% are common in the industry, with some jobs overblown as much as 50%”, says Larry Helminiak, former president of the ICAA, who continues, “the Insulation Contractors Association of America has been engaged in a 15-year crusade to put an end to this.”(2)

Mountain or Mole Hill?
What does an overblow of 25% to 50% mean to a homeowner or builder? According to the Energy Design Update, “The percentage by which fiberglass is overblown equates to the percentage loss in R-value”(3). Stop and think about that. If a homeowner buys an R-38 blown fiberglass insulation job that is overblown by 25%, they actually receive an R-29! If it’s overblown by 50%, they receive an R-19!

Tough to Spot
With most products, it is easy for the consumer to know if they received what they paid for. But not with fiberglass. Most homeowners are unlikely to poke around up in their attic. Even if they do, they won’t spot overblowing because the fiberglass is probably at or near the proper depth, but not the proper density.

The only way to determine if insulation has been overblown is to take a sample of a known volume, weigh it, and calculate its density. This is obviously inconvenient, difficult, and almost never done. But after a decade and a half of pleading with the fiberglass manufacturers, the ICAA decided it was time to document what was really happening in fiberglass insulated attics across America.

Sherlock Homes
Frustrated by the fiberglass industry’s stonewalling, the Insulation Contractors Association of America “organized an independent investigation of attic coverage charts. MaGrann Associates, a building energy conservation and engineering firm, investigated and documented the installation of loose-fill fiberglass insulation in comparison with the attic coverage chart information printed on loose-fill insulation bag labels.”(4)

“The purpose of the study was to observe professional insulation crews installing various loose-fill fiberglass insulation products and compare the field data to attic coverage chart information printed on the product label. The survey was designed to include a geographically varied sample of residential loose-fill fiberglass insulation installations in predominantly flat and open attics.”(5)

The insulation crews knew they were being observed, so there is little doubt that if there is a built in bias in the investigation, it is in the favor of the contractors and the fiberglass insulation. Still, the results are shocking. 79% Failure

“In 79% of the homes we evaluated....the R-value was not achieved.”(6) reported Douglas S. McCleery, PE, the lead investigator for MaGrann Associates. Mr. McCleery explains fiberglass “bag label information remains invalid and will, more than likely, not deliver bag label R-value.”(8)

Perhaps the most stunning finding of the investigation is that “installing loose-fill fiberglass insulation to the required minimum thickness printed on product bag labels is inadequate in 92% of the homes in this study.”(9)

Remember, these crews knew they were being monitored!

Conclusions
Clearly, any builder or homeowner who chooses loose-fill fiberglass insulation is taking his chances - and they’re not good! In 4 out of every 5 homes they can expect to receive an insufficient amount of insulation. Hope!

Fortunately, there is an alternative! Builders and homeowners who choose foam or cellulose insulation do not need to worry. According to Energy Design Update, cellulose is a “short fiber product that can’t be fluffed.”(10) Cellulose is the answer for homeowners and builders who want the R-value they pay for when using a blown in attic insulation.

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For more information on overblowing, a reprint of the article “Deceptive Labeling and Installation Plague Blown-In Fiberglass Jobs”, or for additional copies of this article, please email: This email address is being protected from spambots. You need JavaScript enabled to view it. 

Sources (1) Larry Helminiak, quoted in Energy Design Update, “Deceptive Labeling and Installation Plague Blown-In Fiberglass Jobs”, ( 2) Ibid. (3) Ibid. (4) Insulation Contractors Report, “Independent Investigation Urges Adjustments in Attic Coverage Charts”,(5) Ibid. (6) Insulation Contractors Report, “Interview with Douglas S. McCleery, PE MaGrann Associates’ Prime Investigator”,(7) Ibid. (8) Ibid. (9) MaGrann Associates, “Comparative Information on Fiberglass Loose-Fill Thermal Insulation: Field Installation in Comparison with Manufacturer’s Coverage Charts”, (10) “Deceptive Labeling and Installation Plague Blown-In Fiberglass Jobs”.