Attic Insulation Blown In Cellulose vs Fiberglass?

ovrszd · May 30, 2015

I "think" if the attic is properly vented convection will do the same thing. That's why it's so important to keep the eaves vents open when adding insulation.

What ever happened to those old spinning roof vents?? They were driven by outside wind and had an internal fan mechanism that sucked air out of the attic or roof area as it turned. Used to seem them a lot on old barns and farm buildings.

oldballs · May 30, 2015

Around here some have installed the spinning vents on their homes, but then put plastic bags over them in the winter. I've never figured that one out.

Billrog · May 30, 2015

I would say from my experience you can reduce the heat build up in an attic considerably with proper ventilation. A home I built and lived in with R60 insulation in the attic screened sofet vents, and 2 gable vents no air.c. would get up to 85 degrees by 5 or 6 every day so I added 4 or 5 more vents near the ridge and the home never got above 80 degrees inside after that so this is how I arrived at my opinion.

JimRB · May 30, 2015

Where I live electric powered attic vents are not code. I have continuous ridge vents in the house and barn. I swear but have not measured that my garage attic seems to radiate heat down into the garage. There is no insulation in my garage attic. That problem with go away in a few years if I get to build a big out-building to house cars, tractor and trailers. The garage will become a well-insulated part of the conditioned space.

I have blown cellulose insulation. Cellulose insulation has one advantage over fiberglass in that it does not tend to have convection currents. You can do some research on that, but the theory is that it stops air circulation. I have not noticed any detrimental cellulose settling in my attic, but my insulation is only 18 years old.

Someone mentioned starting the insulation project with a thin layer of sprayed foam followed by your blown insulation of choice. This significantly reduces air infiltration and escape.

rswyan · May 30, 2015

EddieWalker said:
How does moving the air cool the air? It just changes the location of the air. Don't confuse what a fan does on your skin to what it does to the air itself.

I never said it did ... but as KennyG said: it will limit the heat increase (of the air in the attic over ambient outside air temp)