I have understood from insulators that in very cold temperatures fiberglass insulation will actually absorb heat from the house. I have never been able to prove that. Of course, the cellulose insulation guys will suggest that their insulation be blown in over the fiberglass, and problem solved!
What's cellulose insulation? Super chewed up newspaper! If you look at it closely you can see red, blue and green flecks from the funnies! They treat it with Boric acid, so bugs* won't eat it and burrow inside, and blow it in. It is very effective because when laid properly it leaves few gaps. It has a better R-value than fiberglass (3.7 vs. 3.14 per inch) and can be blown into many areas hard to reach with fiberglass.
IT IS VERY UNUSUAL TO SEE BOTH CELLULOSE AND FIBERGLASS INSULATION PUT SIDE BY SIDE INTO A HOUSE WHEN FIRST BUILT. One area may be of one or the other (like steeply-sloped cathedral ceilings, which work best with rolled fiberglass batts) but not side by side.
On a recent thermal investigation, with the typical hot/cold complaints, I saw patterns like this. Red/yellow indicates warm, blue/purple indicates cold.
Not unusual - clearly there is rolled fiberglass insulation where edges have come up, or there are gaps, and heat is escaping. A moisture meter indicated no moisture.
But what was unusual was that this pattern would be on one small aspect of the ceiling and the rest of the ceiling would be perfectly insulated. That is not typical.
I was surprised to get into the attic and see fiberglass and cellulose installed side by side, and apparently at the same time!
It was unusual to see one small area, maybe only 4' long, covered with fiberglass, with cellulose blown all around, but not on top of, that fiberglass. I have never seen that before!
This was a very cold morning. I like early mornings for IR investigations because there is no influence by the sun. The attic space was about 12F! I think my camera is actually looking at fiberglass insulation absorbing heat!
This is a small piece of fiberglass with cellulose all around. Clearly the fiberglass is not insulating as well. Those warm spots are 61F, so heat is moving upward and into the attic space via the insulation. And moving fast!
My recommendation: if you have opportunity to select insulation for your new house, cellulose is affordable and very effective. If you want to add insulation to your existing insulation, cellulose is the same.
And when you add insulation to your existing, what you add is cumulative. If you add R15 to an existing R30 the result is R45. And R45 is very good insulation, especially if all the bypasses, gaps and holes are filled!
* Crazy, nutsy squirrels included...
Jay Markanich Real Estate Inspections, LLC
Based in Bristow, serving all of Northern Virginia.
Office (703) 330-6388 Cell (703) 585-7560