Reflective Insulation In Attic

Ask The Expert – Q & ACategory: Radiant BarrierReflective Insulation In Attic
RIMA Expert Staff asked 4 years ago

I’m obtaining quotes to air seal and insulate the attic in my 50+ year old home. It was recommended to me that additional fiberglass batting be installed over the existing batting to increase the R value. There is an air handling unit and air ducts in the attic. Will it help to add reflective insulation or radiant barrier insulation to fiberglass batting? The most confined space in the attic will have blown-in insulation. Can reflective insulation or a radiant barrier be added over blown-in insulation, be it fiberglass or cellulose? I live in Illinois and like many others in the Midwest, dealt with the polar vortex, icicles and higher utility bills. Thanks for considering my question.

1 Answers
Best Answer
RIMA Expert Staff answered 4 years ago

It would appear you are doing a good job of addressing energy losses in your attic. Although the recommendation of additional mass insulation could be a good thing to do, since I don’t know how much you already have, I cannot comment — beyond noting 2 points to consider:

  1. Any insulation over R-19 generally does not have an acceptable ROI.
  2. Building codes call for an R-30 for attics in your region.

Seems contradictory, but that is the reality, so I would make sure your attic meets code, but no more than that.
As for a radiant barrier application, certainly it would help to have the air ducts covered with a radiant barrier. Installing a radiant barrier on the underside of the roof rafters could aid you in the summer to mitigate air conditioning bills and add comfort in milder temperatures but in your region, it is questionable if you would get an acceptable ROI. Placing a radiant barrier over the insulation on the floor is a controversial application and should only be done when there is no other option. You would also need to take into consideration that dust could accumulate on the surface of the radiant barrier and reduce its performance. I think covering the ducts would be the best option for a radiant barrier use.