In Defense of Cellulose Insulation ...

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I apologize for the poor quality of this photo. Because this is an advertising piece from a spray foam chemical manufacturer, I snapped this picture using my phone.

In the picture, notice half the roof is covered with white frost, (the right side). The other half is bare shingle, (left side).

I’ll get to my opinion in just a moment. But first, let me explain the picture…

Frost on a roof surface indicates that the roof deck is well insulated, and that heat from the space beneath it is not warming the underside of the roof deck, and subsequently thawing the frost.

On the left side of the building, the roof has no frost on the shingles, clearly indicating that the roof deck is being warmed from underneath, and preventing the frost from accumulating.

Without seeing a picture of the attic interior, and knowing more about the quality and thoroughness of the cellulose insulation job, I am left to accept the marketing piece with my "tongue in cheek". 

The “company” is stating that R-30 of cellulose insulation, (about 9”) is allowing the heat from the living space to escape through the insulation... thus, no frost.

When you spray the underside of a roof deck with 5.5” of open cell spray foam (R-19), it indeed seals and insulates that attic. Thus, not enough heat is escaping to thaw the frost.

The picture and the comments must undoubtedly be true, or the manufacturer wouldn’t be making this statement, right?

But maybe they left out some important information, (because they were not aware of it). But, I also know this to be true:

  • Leaky & poorly insulated HVAC air ducts will provide enough heat loss, that a roof deck

will thaw frost. According to the U.S. Dept of Energy, the average HVAC duct system is losing 30% of airflow due to leaks in the air duct system!

  • Without proper air-sealing of ceiling penetrations, bypasses and chasses, an otherwise good R-30 insulation job will allow so much heat loss, that the roof deck will thaw frost.

Without seeing a picture of the attic interior, and knowing more about the quality and thoroughness of the cellulose insulation job, I am left to accept the marketing piece with my “tongue in cheek”.

Here’s Why:

  • It appears that the building is two story.
  • It appears that the building is on a slab foundation.
  • If those two assumptions are correct, I’m left to think that the 2nd floor HVAC and air duct system is located in the attic.
  • The average HVAC air duct system leaks 30%, according to the U.S. Dept of Energy.

From assessing the condition of the parking lot, and the size of the landscape trees, the building age may be 15, or 20 years or more. Of course, this is purely a guess.

That's my two-cents worth. Am I bashing spray foam insulation, heck no! But I think there is more to this advertising piece than is noted on the piece. 

Here are my thoughts:

  1. A spray foam contractor took the picture, during an insulation upgrade, and shared it with his spray foam chemical rep. (I take hundreds of pics a year, and share them freely).
  1. The older, existing cellulose insulation was left in the attic, apparently to be removed after the spray foam insulation was completely installed.
  2. Due to the buildings age, little if no airsealing was performed when the original cellulose insulation was installed.
  3. The upstairs, 2nd floor HVAC system(s) and air duct system(s) are located in the attic space.

Because I am an Applegate cellulose installer (I install Lapolla spray foam, too), I am quick to defend cellulose insulation. When an attic is properly airsealed, a monolithic layer of cellulose insulation at R-30, will leave frost of the roofline. I’ve seen it on my own jobsites, for 18+ years, after installing 5 million pounds of cellulose insulation in thousands of existing homes in the southeast U.S.

That’s my two-cents worth. Am I bashing spray foam insulation, heck no! But I think there is more to this advertising piece than is noted on the piece.

It’s hard to not think that this attic has (an) old leaky HVAC air duct system(s), and no previous airsealing measures in place. Would this same roofline have frost on it, if there is no HVAC in the attic, and proper airsealing measures were employed before the R-30 cellulose was installed? I think so, YES!

But if that was the case… why would you go to the expense of using spray foam in the roofline? If there are no “trades” (HVAC, vulnerable water lines, etc) in the attic, and the ceilings were thoroughly airsealed, I’d bump up the the cellulose to R-50 and move on. Assuming, of course, that the building is in the southeast U.S. It just makes good economic sense.

Contact Bob at the office of Bird Family Insulation, 404-538-9168 or reach us through the contact form on this page.

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