Correct way to install foil faced insulation blanket in attic

Hello everyone.....

I was at a job this past week and was just curious what the insulation experts think of the installation job of this foil faced attic blanket that the H.O. had put in a few years back. She claims to notice a pretty significant improvement in the comfort level of the main floor of the house (1 story above grade) and a decrease in her utility bills - but I can't help but wonder if the crew could have done a better job at installing the attic insulation blankets.

As you can see in the pictures, the blanket was simply laid across the entire attic floor creating peaks and valleys (rising or bumping up over the bottom chord of the roof trusses which creates an air space where the blanket spans over the bays) instead of being cut into sections that could be laid neatly into each bay, ensuring a better fit and contact to the actual attic substrate / floor.

My question is how much difference would this make? My rationale is that in the winter - the foil face (which is on both the top and bottom sides of the fiberglass batt blanket) will end up trapping the warm air in this "air space" (which is actually right above the attic floor) instead of keeping it OUT of the attic altogether and keep it IN and in the main conditioned part of the house.

Any thoughts, or experience with the ideal way to install foil faced attic insulation blankets in a midwest climate? Thanks in advance!

Tags: Attic, attic, blanket, convection, effect, faced, foil, insulation, stack

Replies to This Discussion

Permalink Reply by Sean Lintow Sr on May 15, 2012 at 10:59am

Mid-west = Iowa? aka CZ 5 & 6

A few quick thoughts - Assuming one wants to install it, that is the best place for it based on your climate as it helps prevent the heat from radiating out into the attic & helps block the summer heat from radiating in. In order for it to work you do need an airspace which is why you wouldn't place it directly against the attic floor.

The biggest issues I see & hear is that no air sealing work appears to have been done based on the workmanship, I see no venting / baffles installed, there are two layers which are great at trapping moisture (shoot even the one layer maybe an issue), and seeing that it is integrated in the batts that they didn't fix the initial insulation first and install the product as the manufacturer recommends.

I would say that it needs to be pulled, the air sealing work done, venting issues addressed, cellulose blown in an even layer that goes above the top of the truss chord & then the product is laid down again.Oh & by the way, I hate to say this, but as the product gets dirty it will lose it's effectiveness.

Permalink Reply by Joshua Knittel on May 16, 2012 at 9:28am

Thanks for the feedback Sean.....yeah, the homeowner had the insulation blanket installed by a company that was strictly insulation a few years back. I'm heading back to that job to do the actual audit in a few weeks, just thought I'd share some of the preliminary photos I took. And yes, Iowa....thanks again!

Permalink Reply by Robert H on May 17, 2012 at 10:05pm

I would say that radiant barriers in the midwest are a waste of money. Radiant barrier work best when there is little insulation. Do some research and you will see home that have an R value of less than 20 will see the greatest benefit. Above that the the effectiveness of the barrier declines. You will see at an R40 or above the benefit will be so small that it is not economically feasible.

If you were to seal air leaks and bring the R value up to an R 40 or higher you would receive a greater benefit and that should be the starting point regradless. . Again once you do that it does not pay to install a barrier. It you still have money in your budget then you should look at something else that would save more energy with a similar invest to the RB.

I do see in the picture what appears to be fiberglass batts. If it was a typical installation the batts were not installed to maximum efficiency.

I am not a fan of fiberglass in attic installations and would recommend cellulose.

Radiant barriers have limited use, southern homes. I will add that the FSEC has stated that radiant barriers show a significant reduction in reflectivity do to dust accumulation.

So what is the proper way to install the radiant barrier in the midwest,,,,leave it on the store shelf.

Permalink Reply by Robert Riversong on September 4, 2012 at 7:56pm

Ditto.

If that foil sandwich is a supplement to existing minimal fiberglass batts, then it will have some enhancement effect, by reducing convection in the fiberglass and by creating a modest (though dusty) radiant barrier, which will help reduce summer heat gain more than winter heat loss, and by very slightly reducing thermal bridging through the bottom chords.

That the two layers of foil have a half-inch of fiberglass sandwiched between them does not make it an "insulation blanket" (as it would have no more than R-1.7), but merely a radiant barrier.

I agree that the cost-effective approach would have been air-sealing the ceiling and blowing cellulose in the attic. Venting the attic is always a good idea, except in humid coastal climates.

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