Mylar film on top of insulation

I’m up in Vermont so we tend to design insulation systems for the cold weather. I just inspected a house that had a reflective mylar film over the TOP of the insulation in the attic. I’ve never seen this, and I know it is wrong, but I don’t know what the product is or why anyone would have installed it this way. Check out the photos below. Any thoughts on how I should write this up?

It’s a radiant barrier.

As to whether or not it’s of much use or not I’ll leave that to others.

Agree Tom. How well it works is a question to be answered but it is not a defect.

Correct, not a defect.

I don’t know much about radiant barriers but would it make more sense to be installed on the underside of the rafters?
I’m sure someone will have an opinion on that…:wink:

Why is that not a defect? It’s installed on top of the insulation which acts as a vapor barrier.

BTW, that is not mylar.


In my experience these radiant barriers are micro perforated to allow moisture, air passage.

Some of them do have the holes, the OP’s example does not. Even it was high perm, as soon as the dust takes over, it’s no longer a radiant barrier.

Agree, but with the accumulation of dust, it will lower its performance and not lower the attic temperature, but reflect it from going down in the habitable space below.

Installing On Attic Floor

Suggested Product: RadiantGUARD® Ultima-foil radiant barrier breathable (this version is perforated to allow moisture from home to easily pass through and out of your home).

It’s not supposed to be sealed at the edges just laid on top of the insulation. If done this way it can breath and not a defect.

Not a defect.
Tests have shown it stops working when it gets dusty but it is made to go on top of the insulation.
I suppose you can call out its dusty and taped?

Sorry Paul, but unless it has a perm rating of at least 10, it’s not designed to go over the attic floor insulation. Low perm, low E radiant barrier is designed to be fastened to the underside of the rafters. I don’t believe that just not taping the joints is going to work well. Of course, the climate zone will have something to do with this.

Brad, they sell the stuff to lay over insulation as I remember. I also remember confetti like flakes you sprayed over the fiberglass or cellulose that was also intended to act as a radiant barrier. Either way in a perfect world it works great but since we don’t live there it hardly does anything.

I’ll agree with you as I’m not sure but still, I would not write it up as a defect. How would you explain that if asked?

Thanks Kenn, I will have nightmares tonight wondering if I have a one sided or two sided vapor barrier and if its perforated or not.

Technically speaking you could use aluminum foil and get the reflectivity but then your screwed as far as moisture entrapment.

Screw this, I am going back to being a GC, at least then I didn’t have to think about stuff so much.

Kudos to Mr Rammbo…:mrgreen:

I remember seeing that 40 yrs ago in attics but again they were just laid in there and not taped and I really don’t remember seeing any problems.

All this talk has made me want ice cream. Gonna get the wife and her dog into the car and hit Izzy’s for a waffle cone of banana.

Your going to see the Dr. now after Mexican food for a week now ice cream. :shock::shock:

I want a banana split burrito with lots o jalapeños!

Good article Ken. Thanks