Adding Attic Insulation over fiber glass loose fill


Old 08-25-14, 06:21 PM
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Join Date: Mar 2006
Posts: 8
Adding Attic Insulation over fiber glass loose fill


I'm hoping to add some insulation in my attic on top of the fiber glass loose fill already there. The current insulation covers the rafters by just a few inches.

Must I use loose fill on top of this? (which would require a contractor and the equipment). Or can I simply get the blanket roll kind and have at it?

Also need an understanding for how much I should add. This home is in the north east, so we get some cold winters.

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Old 08-25-14, 07:21 PM
Join Date: Jan 2014
Location: usa
Posts: 466
If your bottom truss chord is a 2"x4" and the insulation is a few inches over it then you are insulated to an approximate R-19. You should be at a level of R-38 to R-49. You can add unfaced fiberglass roll or batt insulation over the existing since they are of a similar density. Usually the effort of maneuvering about the attic to install the batts will wreak havoc on the loose fill material and you will have to be careful about disturbing it too much. Also make sure to wear a respirator as those loose fibers can really tickle your throat.

It would also be worth the effort to build up the level of insulation over your ductwork as the R-value of the original material is probably very low.

There are other considerations such as air sealing construction and mechanical gaps in the interior air barrier, namely the drywall or plaster finish. Perhaps reviewing the location of ceiling lighting fixtures, duct vents, etc. would be of value and you may be able to do a respectable job of sealing gaps around them from the living space side of the dwelling. This is all in an effort to control airflow from the conditioned area to the attic which certainly contributes to heat loss and should be viewed with a critical eye.
Old 08-25-14, 08:25 PM
Thread Starter
Join Date: Mar 2006
Posts: 8
Thanks I was hoping for this answer. Should I install baffles? Or is it good enough to just make sure I have an air flow gap?
Old 08-25-14, 08:51 PM
Join Date: Oct 2008
Location: New England
Posts: 9,999
The baffles will perform two functions. One they help to maintain an air path below the roof deck and two they reduce the air infiltration through the insulation itself. Ideally the baffles should also protect the end of the insulation near the soffits. See attached link.

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