Low E Barrier Under Asphalt Shingles

[Brian Hannigan]

I am going to have a new asphalt shingle roof installed and I have the option (at $3k) to have a Low E Barrier installed that reflects heat.

I have a few questions that I hope some of you have answers to or experience with.

First, our home is 1,350sqft (+ 2 car attached garage) in So Cal about a mile from the beach. We do not have AC but I'm going to install a whole house fan (more questions on that to be posted in another thread), and we have a natural gas FAU in the attic.

Seeing that there will not be a large energy savings because of no AC do you think the cost is worth the comfort of what I hope would be a cooler home on those hot days that are about 2 months out of the year? I know this is subjective but have you had experience and does a low e barrier really keep the house cooler?

My other question/concern is, does the fact that it is reflecting heat directly under the shingle effect the lifespan of shingles or warranty from the manufacturer?

If you have personal experience can you share the pros/cons?

A big "THANK YOU" to all of you in advance!

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[Scott Patterson]

I have not seen a radiant barrier installed under shingles. I have seen the barrier in the attic side with some of the newer roof decking systems. I would check with the shingle manufacturer and get their thoughts before going with it. I honestly do not know how it will perform but logic tells me that it might cook the shingles!

[David Wigger]

I have not seen a radiant barrier installed under shingles. I have seen the barrier in the attic side with some of the newer roof decking systems. I would check with the shingle manufacturer and get their thoughts before going with it. I honestly do not know how it will perform but logic tells me that it might cook the shingles!

I'm with Scott.
The one thing I would focus on is making sure you have the best attic ventilation possible. My preference is a ridge vent with plenty of soffit vents. Years of walking in attics have proven to me that this combination yields a much cooler attic.

[Markus Keller]

Haven't heard of this either. I would also be suspicious of the material potentially cooking the shingles. For my money I would probably look into good insulation under the roof or insulation board on the top side. Pro's and Con's to both options depending on material used etc. Good insulation can dramatically cut down on the heat gain, add in a good ridge vent or other venting means and you can get rid of a lot of heat to avoid AC.
My recommendation is that you get the exact material make and model information from the contractor. this allows you to look up the material, see if its approved for the use, limitations, specifications, etc. If the contractor won't give you the manufacturer / model info then you can figure its a load of BS.
I don't know how many times a contractor has specified a product for a client, you look up the product and its not even recommended for that use.
there are probably better options for that $3K.
Maybe look on Joe Lub.'s site, building science and see if he has any info about that idea.

[Jeff Euriech]

Brian,

Is a Low E Barrier the same thing as a radiant barrier?

We have radiant barriers here in the attics in Arizona. There are two types that I often see. One is on the backside of the roof sheeting and the other one is installed on the attic floor.

The one on the roof sheeting works very well. I can tell a big difference when I go into an attic in the middle of summertime.

The radiant barrier on the floor doesn't seem to do much at all.

There are some concerns about heat being reflected back up through the shingles and decreasing the life expectancies of the roof. (I have not noticed a difference on the roofs that I have seen.) Also note: There is some concern with lighting strikes causing the radiant barrier to overheat and start a fire.

http://www.texasinspector.com/files/...Article-II.pdf

Jeff Euriech
Peoria Arizona

[Jerry Peck]

I would consider similar to what Markus described - insulation on the underside of the roof sheathing (with roof deck insulation on top of the roof sheathing and shingles, you would require a layer of sheathing over the insulation to serve as the nailing surface for the shingles.

Insulate the underside of the roof sheathing and seal the attic up (no ventilation).

And, yes, https://www.buildingscience.com has lots of excellent information.

[CoronadoBruin]

In a word, no, not at that price and not where you live. A whole house fan works wonders in keeping the attic cool. I have some knowledge of your area as my father lives in Capo Beach and I just moved from being right on the water in San Diego. Insulation and air movement, both in your attic and the living areas, will be adequate. However, having moved to Palm Desert two years ago....

[Larry Morrison]

If this is a Radiant Barrier (Lo-E may be different) remember that it will need an airspace to work. The Radiant Barrier applied to the underside of the roof deck works well (the airspace is the attic) and these should be perforated (or you will play heck finding a roof leak). The Radiant barriers (foil) that are applied over the insulation (also need to be perforated) will work only so long, since they get dirty on top and the airspace is no longer effective.

I can see where a Radiant Barrier / (Low-E) would work under a tile that has an airspace by design.

I would be interested in seeing the manufacturers specs and install instructions for the product you are considering.

[Matthew Steger]

I have not seen a radiant barrier installed under shingles. I have seen the barrier in the attic side with some of the newer roof decking systems. I would check with the shingle manufacturer and get their thoughts before going with it. I honestly do not know how it will perform but logic tells me that it might cook the shingles!

I agree with Scott.. find out from the shingle manufacturer if there is an issue installing what you are referring to under the shingles. I would think it could potentially damage the shingles more than any benefit you'd see.

[Gunnar Alquist]

Brian,

I am going to agree with others earlier. Dana Point is pretty mild and I suspect there is going to be limited benefit from any radiant barrier (or similar) product. I rather doubt that you would see a $3000 savings over 30 years. If you were in the Mojave region, it might be a different story.

It might be helpful if we could know more about the proposed material. Do you happen to know the brand & model? If we had that, we could look at the online information and possibly give you more information.

[Brian Hannigan]

Thank you for all the replies and input on this.

With the information you provided I will opt out of the Low E Barrier and just go with the Whole House Fan.

I will however get more info about what barrier they use and how it is applied and post that info back on here.

Thanks again for all your help!

[Brian Hannigan]

Ben Jacks sent me an email asking some other questions so I thought I'd share here if other have the same questions.

"Hi Brian,Saw your thread and wanted to comment on roofing and wanted to know house age, type of roof/attic, existing sheathing...skip or ply etc. vaulting?"

The house was built in 1962. This may be the original wood shake roof. Would that be crazy or perhaps it was replaced long long ago. Along with the few big holes that are in it there are burned out sections in almost all the shingles. Too many to keep patching.

The shingles are over skipped sheathing and there is an attic. This is a single story home.

I have 3 gable vents and soffit vents all around.

Thanks to very one for all your help!

[Ben Jacks]

Ben Jacks sent me an email asking some other questions so I thought I'd share here if other have the same questions.

"Hi Brian,Saw your thread and wanted to comment on roofing and wanted to know house age, type of roof/attic, existing sheathing...skip or ply etc. vaulting?"

The house was built in 1962. This may be the original wood shake roof. Would that be crazy or perhaps it was replaced long long ago. Along with the few big holes that are in it there are burned out sections in almost all the shingles. Too many to keep patching.

The shingles are over skipped sheathing and there is an attic. This is a single story home.

I have 3 gable vents and soffit vents all around.

Thanks to very one for all your help!

From what you describe, the best bet is using an A rated fiber three tab cover, good cross vent attic circulation and the whole house internal exhaust as you plan for summer cooling. To retro upgrade the stick frame configuration would take a lot of sealing that Low E with an air gap would not effectively cover. rbj

[Elizabeth Chambers]

I would do some research on whole-house fans if I were you.

[Ben Jacks]

I would do some research on whole-house fans if I were you.

Dear Elizabeth,
I know what you mean. A whole house fan install for air scavenged recirculation in conjunction with the HVAC system in a sealed house is what Brian may be referring to I hope. Not an easy undertaking for a 1962 vintage house. Thanks for your suggestion.

[Jerry Peck]

Ben,

I'm thinking Brian was referring to an unsealed house with no HVAC (other than exhaust fans and heat - i.e. no air conditioning).

Whole house fans have a tendency to depressurize the house and suck outdoor air in through every crack and crevice ... which is not that much of an issue when the windows are open - which is what I am envisioning with Brian's additional information.

[Brian Hannigan]

Ben,

I'm thinking Brian was referring to an unsealed house with no HVAC (other than exhaust fans and heat - i.e. no air conditioning).

Whole house fans have a tendency to depressurize the house and suck outdoor air in through every crack and crevice ... which is not that much of an issue when the windows are open - which is what I am envisioning with Brian's additional information.

Jerry is correct, no HVAC and the purpose that we here in a SoCal beach city use it for is to suck in the cool outside air in the late afternoon and evening. Doors & windows open when in use.

[Robert Sole]

I am going to have a new asphalt shingle roof installed and I have the option (at $3k) to have a Low E Barrier installed that reflects heat.

I don't have any experience with it but I did find this. http://www.low-e.com/roofing.html

[Ben Jacks]

Jerry is correct, no HVAC and the purpose that we here in a SoCal beach city use it for is to suck in the cool outside air in the late afternoon and evening. Doors & windows open when in use.

My apologies for the response I gave to Elizabeth about a clarified research. The Low E blanket under the three-tab must have an air gap. Direct felt and shingle contact to the foil will create a conductive transfer that negates the reflective isolated feature. Note the detail of furring being placed over the foil/foam blanket shown in the linked Low E web example to create the air space.

Brian, I understand the direction of the economics taken considering what you have to work with and I would do the same. rbj

[Elizabeth Chambers]

That s ok Ben, I did not understand your response anyway. Also I responded before I had fully comprehended the question.

I was thinking of the wholehouse fan sucking moisture into the home because the location is so close to the beach. Probably would not be a problem tho.