Thursday, October 31, 2013

A word about loose-fill fiberglass in attics: "No!"

Along with stopping air leakage into/out of the home, the strength of your attic is frequently the biggest factor in determining how well your home can protect you from the cold in winter months.  Strong attics create comfort.  So when a homeowner is told that they have 12” of insulation in their attic, that might just sound reasonable (it's close).  Except that it depends on what material constitutes that 12” of insulation.  This infrared image of a ceiling at a home in Hecker, IL provides a case in point:  

Orange = warm, Blue = cold

Why does this ceiling look like it’s been tye-dyed?   The answer is in the 12” of insulation material.

Too much cold air is getting through the 12” of loose-fill fiberglass insulation** in the attic and is reaching this ceiling...thereby making the drywall on the ceiling cold.  And since the insulation is so porous and unevenly distributed, cold air gets down to the ceiling in pockets of least resistance and it shows up under infrared (in blue).  This is happening in every room of the house, and this "sucking" of heat from the ceiling through the fiberglass and into the attic space is called convective heat loss.  Because of the cold ceiling:

--The problem of convective looping is amplified, which exacerbates comfort issues.   
--More heating fuel is used, at cost to the homeowner.
--Heating equipment and air distribution fans run longer, at cost to the homeowner.
--Overworked heating equipment needs replaced more frequently, at cost to the homeowner.     

Worse, we see evidence that previous installers are either using installation techniques that “fluff” loose-fill fiberglass and result in lower densities (and lower performance), or install a popular, less-expensive fiberglass product that is only rated for walls…or both.  12” of loose-fill fiberglass with these two factors reduces RValues to near R10.  Scary thought: We see this inappropriate use of loose-fill fiberglass most often in houses that are built in the last 15 years. 
But this is not a new phenomenon.  Loose-fill fiberglass in attics used to perform much worse.  Back in the 90’s, loose-fill fiberglass manufacturers were called out on this poor winter performance and in 1992 the State of Minnesota began requiring fiberglass manufacturers to acknowledge this in their material documents.  It’s a practice that continues to this day.  Improvements to loose-fill fiberglass products have helped to mitigate this convective heat loss, but it can’t be stopped with loose-fill fiberglass to the same degree that cellulose can.

The great news is that all is not lost if you have the white fluffy stuff in your attic that can produce the tye-dyed ceilings.  A thin layer (at least 3”) of loose-fill cellulose on top of the existing fiberglass restores the fiberglass' true RValue and knocks out the convective heat loss problem.  Problem solved, cellulose to the rescue.
NOTE: We love loose-fill fiberglass when it is dense-packed in wall cavities.  Studies indicate dense-pack fiberglass provides higher RValue in a closed wall cavity than cellulose can achieve in that same cavity.  It works.  Bravo!  Just don’t use it in an attic.   Also, fiberglass batts--because of their construction--are slightly less susceptible to convective heat loss that plagues loose-fill fiberglass.  Neither approach the performance of cellulose in an attic.      

If you  have any questions about our products and our philosophy on all insulation materials, see our “Insulation” page.

**12” of cellulose gives you an R42.  12” of loose-fill fiberglass creates an R30.  What’s the difference between the two?  Cellulose is constituted of shorter, denser fibers which allow cellulose to cozy up real snug with other cellulose fibers.  And it’s a little heavier, which means it fills in gaps and lays ‘tightly’.  Because of this, there’s less opportunity for air to migrate through the cellulose material.  Loose-fill fiberglass has longer fibers, provides less resistance to air movement, and allows for the convective heat loss effect that shows up in the infrared picture above.