Thread: foil in attic

Attic this am. All attic roof framing covered with foil (not insulation) ie; stapled to bottom of rafters. Looked like a home made attempt to install radiant barrier. There are holes poked in the area of the roof vents. Haven't seen this before. Thoughts?? Sorry - couldn't load pic here.

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There is a foil type radiant barrier which goes on like that - is stapled to the underside of the truss top chords or rafters.

Hmmm! My thoughts. Looks like it would trap heat and moisture between the decking and the foil - doesn't seem like that could be a good thing. You think it would effect the roof shingle warranty / peformance?
edit - wouldn't condensation build up on the foil and go down to somewhere??

Originally Posted by Richard Stanley

Hmmm! My thoughts. Looks like it would trap heat and moisture between the decking and the foil - doesn't seem like that could be a good thing. You think it would effect the roof shingle warranty / peformance?

My thoughts too. But supposedly good research as shown that the effect is limited. Although there is a trade off (albeit limited) for roof life for less cooling cost. Myself, though, would trade off a little more monthly cooling cost for a little longer times between BIG roof replacement costs.

Might just be me, though.

edit - wouldn't condensation build up on the foil and go down to somewhere??

Not if properly vented.

Never did figure out this one.

Eric,

The Mel Gibson Movie Signs comes to mind. Those tin foil hats Get Hot why not get complete Protection and just cover the attic?

Billy, MAybe they just had extra foil left over after the BBQ.
I see this all the time on 1900'S home and have never seen a moisture problem created due to the usual 6 inch gap between underlayment and foil. I ve seen some in newer homes to insulate air handler areas below wood roofs too.
In the home I recently built overseas they insist that the foil reflects heat.
I'm not convinced, YET

Eric,

I thought the same thing as Bill. Alien transmission for sure.

I ran across this recently.

Originally Posted by wayne soper

In the home I recently built overseas they insist that the foil reflects heat.
I'm not convinced, YET

It does.

That's why we have concerns regarding the roof covering above ... it just gets re-heated with the reflected heat.

Eric,

That's one type of foil, and one of the problems with it.

Bruce,

While the foil does work when installed on the bottom chords like that, the reason it is recommended to be installed on the bottom of the top chords (or rafters) is that dust will settle on the foil when installed on the bottom chords (or ceiling joist) as shown in your photo - a little dust and the reflectivity drops significantly, give it a few years for it to collect more dust and the foil heat reflective barrier might as well not even be there.

If you noticed, that was perforated to allow moisture vapor through - you do not want to install non-perforated on the attic floor as that stuff non-perforated foil) is good at keeping moisture from passing through too.

Ever seen those ads on TV for 'solar film', 'solar blanket', 'invented for NASA', blah, blah, blah? Similar stuff in that the main purpose is to reflect heat. Which gets us back to where we started ...

... Is it detrimental to the roof covering?

Jerry, I seem to remember Dr. Joe had a study about radiant barrier, (but I may be confusing it with attic venting) that indicated the color of shingles had a much greater effect on the temperature and life of the shingles than other factors. White or light colored shingles perform better than dark.
I would look it up, but I have not been able to find much of anything since they redesigned the site.

On a common sense note (since I have no emperical evidence) if you stop the radiant energy from being transmitted into the attic and reduce the attic temperature by bouncing the radiant energy back toward the sky, then the cooler conductive/convective energy space in the attic would tend to mitigate the additional energy bounced back to the shingles. The rate of energy radiation back to the sky is higher as the temperature goes up. I think the general idea is that the radiant barrier reflects energy rather than allowing the house to absorb it.

I am not totally sold on the radiant barrier, but I think there is a valid theory at work if a standardized approach can be put forth with quantified results from a reputable source. The trouble now IMHO is the snake oil salesmen with unsubstantiated and over stated claims of energy savings.
Radiant barriers have to be designed as part of the attic/roof system. Just stapling some stuff up in the attic without understanding the entire system (ventilation, insulation) at work could actually hurt the energy consumption and maybe the house.
Just my opinion, put that with $5 and you might get a cup of coffee

Originally Posted by Jim Luttrall

Jerry, I seem to remember Dr. Joe had a study about radiant barrier, (but I may be confusing it with attic venting) that indicated the color of shingles had a much greater effect on the temperature and life of the shingles than other factors. White or light colored shingles perform better than dark. I would look it up, but I have not been able to find much of anything since they redesigned the site.

I believe that was a study done by the Florida Solar Energy Commission, and, yes, the darker shingles were hotter than the lighter shingles, and, yes, the radiant barrier did have some effect of the shingles temperature raising - but the color of the shingles had a greater effect on shingle temperature.

I think the general idea is that the radiant barrier reflects energy rather than allowing the house to absorb it.

Correct, which is why a radiant barrier reflects that radiant heat back up to the roof. A radiant barrier is a reflector of energy, not an absorber of energy.

I will post pictures of the install when I get around to it in about a week or so. Will be laying it over the blown in cellulose on the floor and stapling from bottom of rafter up to the ridge. Of course, all of this AFTER I go vacuum out all the cellulose the geniuses blew into the eaves.

FYI...Radiant barrier reflective insulation systems from Innovative Insulation Inc.

I'd like to hear other opinions and I will also be tracking my heating costs versus last year and recalculate usage based on current rates and usage amount. This will be interesting.

And if the RB was able to reduce attic temps, which in turn would keep the decking and shingles cooler, wouldn't I be at least "even" in terms of shingle life if not ahead by a bit?

Originally Posted by Ross Neag

I will post pictures of the install when I get around to it in about a week or so. Will be laying it over the blown in cellulose on the floor and stapling from bottom of rafter up to the ridge. Of course, all of this AFTER I go vacuum out all the cellulose the geniuses blew into the eaves.

FYI...Radiant barrier reflective insulation systems from Innovative Insulation Inc.

I hope that product is better than their water heater radiant barrier product as most water heater manufacturers tell you NOT to wrap the water heater. Years ago (a decade or two) water heaters were not as well insulated as they are today, *back then* wrapping the water heater actually may have done some good. Today, however, with the better insulation produced on water heaters, wrapping the water heater can lead to condensation forming on the steel outer housing of the water heater, causing it to rust out.

I'd like to hear other opinions and I will also be tracking my heating costs versus last year and recalculate usage based on current rates and usage amount. This will be interesting.

You will need to be able to track your costs back a few years to get any meaningful data. Any slight changes in average temperatures will skew your comparison from just one year to the next year, unless you also go back and compare weather data between the two years and the weather data is the same.

And if the RB was able to reduce attic temps, which in turn would keep the decking and shingles cooler, wouldn't I be at least "even" in terms of shingle life if not ahead by a bit?

Nope.

The attic and roof are now separated by the radiant barrier, which reflects the heat back up to the roof sheathing (and is why the attic is cooler - the roof is hotter by the heat not getting to the attic).

Shorter shingle life. How much shorter is unknown - measurable or not ... don't know.

And if the RB was able to reduce attic temps, which in turn would keep the decking and shingles cooler, wouldn't I be at least "even" in terms of shingle life if not ahead by a bit?

I think the jury is still out on that verdict. But there is at least some validity to your theory. You will have an increase in radiant energy to the shingles, but since the temperature of the attic will be cooler, there will be an offset with greater conduction and convection energy loss from the shingles to the attic and there will also be an increase in radiant energy loss to the sky since not all radiant energy will be absorbed by the shingles on either the inbound or outbound path.
If there was a significant measurable increase in shingle temperature or decrease in shingle life, rest assured the shingle manufacturers would be denying warranty coverage on that basis. I have not heard of that, has anyone else?

Had a nice talk on the phone with JP Bolton, Vice President of sales of Innovative Insulation. Here's what transpired in email form. I have no affiliation with that company, for the record.

Hello Ross,

You are absolutely correct in your assessment. Tests were conducted to determine the possibility of overheating shingles and causing premature curling and roof system failure. The most interesting aspects of this has been the several contractors who have called me and told me they had OBSERVED this shingle failure situation. THEY WERE LYING!

I have attached the test for your review.

This was the premise: Radiant barrier installed would reflect the heat thereby doubling the temperature of the shingles.

Two identical homes, one with barrier and one without, were subjected to hourly shingle temperature measurements. Over the course of the test we found that during the PEAK HEAT OF THE DAY, the shingles on the home WITH barrier were indeed higher than the home without. Unfortunately for Owens Corning who desired a large temperature problem,the difference was never more than 5 degrees. This is an insignificant increase in temperature for a shingle designed to work any where from dessert to cold climates. More unfortunate for Owens Corning, after the PEAK HEAT OF THE DAY, the shingles on the roof WITH the barrier were as much as 8 degrees COOLER than the home without. Over the course of the test period the home WITH BARRIER had an average shingle temperature 6 degrees COOLER than the home without barrier.

What had occurred was that the home without the barrier had built up a reservoir of heat in the attic during the day and that heat had kept the roof hot re-radiating that heat when the heat source (Sun) was removed. The home with the barrier had never built up a reservoir of heat and had gone ambient as soon as the heat source was removed.

As a result of this test all the shingle manufacturers have issued letters that the installation of radiant barriers will NOT affect shingle warranties. So, next time some contractor tells you that he has OBSERVED this shingle failure, (or vinyl siding failure) due to the excessive heat caused by radiant barrier installation, you might ask him what planet this occurred on because it was not earth.

Please pardon my extreme feelings about this, but I have had several run ins with contractors over this issue and I have a large burr under my saddle over this subject. J. P.

J.P. Bolton

Vice President of Sales

Innovative Insulation Inc.

6200 W. Pioneer Pkwy

Arlington, TX. 76013

800 825 0123

Radiant barrier reflective insulation systems from Innovative Insulation Inc.

jp@radiantbarrier.com

From: Ross Neag [mailto:jasrwn@comcast.net]
Sent: Wednesday, October 31, 2007 10:21 PM
To: Innovative Insulation Information
Subject: Having a discussion about shingle temperatures and radiant barriers

Hello. I am a customer of yours and a licensed home inspector in Chicago. Some colleagues and I were having a discussion about installing radiant barriers either under the roof decking or to the bottom of rafters and its affect on shingle temperature. I believe that if you are able to keep the inside of your attic noticeably cooler that the only possible negative effect would be the radiant energy bouncing back to the underside of the shingle. I argued it is minimal at best and that some shingle manufacturers would have already voided warranties if it could be proved that RB was used. The reduction in interior temperature and its corresponding cooling effect of other building components, especially the longer amount of time for things to heat up, all play a beneficial part in PROLONGING roofing materials.

I’d like to hear your opinion, either by email or phone. Thanks in advance…

Ross Neag
708 243 7222

Ross,

The "FSEC" study reference on that document is the same one I referenced in my post on 10-16 above "study done by the Florida Solar Energy Commission".