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Musings of an Energy Nerd

Do Foil-Faced Building Products Block Cell Phone Reception?

The Energy Nerd tries to track down answers to longstanding questions about radiant barriers and cell phones

Can radiant barrier sheathing block cell phone signals? According to Robert Palardy, manager of technology at Louisiana-Pacific, “Radiant barrier sheathing does have a thin layer of aluminum on it, so it is certainly possible that it could affect a cell phone signal in a small way. It’s likely to be a smaller effect than many other factors, but if the signal is already weak, it could be a measurable effect.”
Image Credit: Louisiana-Pacific

It’s increasingly common for builders to install rigid foam on exterior walls and roofs. And among green builders, polyisocyanurate foam — a type of foam that often comes with foil facing — is generally perceived as the most environmentally friendly foam available.

The popularity of foil-faced building products raises an interesting question: If you install foil-faced foam or a radiant barrier on your walls or roof, will the foil interfere with cell phone reception in your house? In hopes of pinning down some answers, I recently posed the question to several experts and building material suppliers.

The answers I received were inconsistent. Representing one end of the spectrum was an unidentified spokesperson for cell phone provider T-Mobile. The spokesperson was quoted by Lauren Koszarek, an employee of Waggener Edstrom Public Relations; according to Koszarek, it is T-Mobile’s position that foil-faced building products “can sometimes act as reflectors to signals or can block signals so that they do not penetrate into the structure.”

Representing the other end of the spectrum is Mary Edmondson, the executive director of the Reflective Insulation Manufacturers Association (RIMA), who said, “There have been no studies that indicate there is any interference with cell phone usage where a radiant barrier is present. In other words, no, reflective products do not affect cell phone reception inside a house or structure where both are present.”

Homeowner complaints

To begin our investigation of this issue, let’s look at some complaints about cell-phone problems attributed to foil-faced building products.

I recently received an e-mail from Don Johnson of Nassau Bay, Texas, whose complaint is typical of the genre. “I had a new roof installed a couple of years ago and the installer asked if I wanted a radiant barrier on the foam insulation,” Johnson wrote. “I thought that it would…

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31 Comments

  1. Daniel Morrison | | #1

    My DIY test results
    I wrapped my phone in aluminum foil and called it. I wasn't home -- the call went straight to voicemail.

    Next, I unwrapped the phone and laid the foil on top, like a tent, and called. The phone rang.

    It seems that the signal got through the windows and walls of the tent, but cannot get through the faraday foil.

    This raises an important question: what happens if I wrap my Mother-in-Law with foil?

  2. Aj Builder, Upstate NY Zone 6a | | #2

    Moisture and breathing issues
    Moisture and breathing issues may arise Dan

  3. GBA Editor
    Martin Holladay | | #3

    My test results
    Test #1: No foil. Phone rings.

    Test #2: Wrapped with a single layer of foil. Phone does not ring.

    Test #3: One layer of foil on top of the cell phone like a tent. Phone does not ring.

  4. Dan Kolbert | | #4

    Wall thickness
    We've noticed that super-insulated homes in general seem to have an effect on cell reception. We recently wrapped a house in asphalt-faced polyiso (4" on the outside, 6" of cellulose on the inside) and noticed crappy cell signal inside. There is also a metal roof, so perhaps that is the problem. And the reception was marginal already.

    We had the same issue in another new home (12" walls, 14" roof, dense-pack cellulose) with asphalt shingles. Again, the reception was marginal already.

  5. Jeff Haines | | #5

    Metal Roofs
    Another fine post. Now could you do the same research on metal roofing? We installed galvanized metal roofing on our house shortly after buying it 8 years ago, and we have lousy reception. I don't recall how reception was before it was installed, but lately it's been so bad that we lose calls if we don't step outside to talk.

  6. GBA Editor
    Martin Holladay | | #6

    Response to Jeff Haines
    Jeff,
    Several of the people I interviewed mentioned that metal roofing can interfere with cell phone reception. One of them (Robert Palardy) was quoted in the article. Palardy said, “There are plenty of documented cases where people report diminished reception in houses with aluminum siding and metal roofs.”

    It sounds as if you may want to look into installing a cell phone signal booster.

  7. Bob Coleman | | #7

    faraday cage
    It's not a faraday cage unless its properly grounded, and of course all the foil would have to properly contact/ground to each other piece of foil. Metals roofs which should be grounded in most cases could definitely be an issue; radio and CB transmission into metal buildings is a long time known issue.

    A better test is to take a sheet of polyiso and build a small box, cut in represenative window or two, set phone on table in yard and cover with box, give it a call, then send some text msgs as the cell tower will retry those. Doesn't represent the typical interior distance though.

  8. Dick Russell | | #8

    Wireless routers affected, too?
    FWIW, I have noted that the laptop PC in my office shows only low signal strength, one or two bars out of five, between the PC and the wireless router, which sits on a shelf about 25 feet or so in a direct line. The router is one floor lower, and in that direct line is a collection of air ducts made of foil-surfaced ductboard. If I move the router to the side a few feet (but in a precarious position), signal strength improves dramatically.

  9. Bill Costain | | #9

    Response to Daniel Morrison
    "This raises an important question: what happens if I wrap my Mother-in-Law with foil?"

    Obviously we can't answer your question unless you tell us what climate zone she is in.

  10. Keith Gustafson | | #10

    How come I cannot hear my
    How come I cannot hear my phone when I have my tin foil hat on?

    Everything blocks radio signals

    foil worse than paper

    If you have one bar and walk into a foil house your call will drop

    If you have 4 bars it won't

  11. Doug McEvers | | #11

    Next great idea
    Connect the cellphone booster to the foil sheathing to create a giant antenna. Be prepared for some cosmic chatter.

  12. Aj Builder, Upstate NY Zone 6a | | #12

    If still wrapped, said
    If still wrapped, said Mother-in-Law may need unwrapping at this point. Beware that there may be a large release of pent up signalling. However if the foiling plot was foiled, via foul play or from foolish frivolity, well we are finished then here and forthwith.

  13. Ken Dupuis | | #13

    My anecdotal 2 cents
    I've built 2 additions and rehabbed one house where I wrapped the structure in Dow Tuff-R foil backed insulation. In all 3 cases, there is no cell phone reception in the structure. One of the additions was on my own house. Cell phones don't work in the Master bedroom or living room (which I think is a good thing). On the other 2 jobs, contractors were annoyed because they kept missing business calls while inside the building.

  14. Mark Walter | | #14

    What about aircraft hulls?
    Think for a moment about aluminum aircraft hulls. That skin is quite thick, the windows are relatively small and the aluminum forms electrically complete connections yet the cell reception on the ground is quite good. Perhaps the windows, small as they are, are very important for radio signals to pass.

  15. GBA Editor
    Martin Holladay | | #15

    Response to Mark Walter
    Mark,
    For a Faraday cage to be effective, the metal shield needs to be grounded.

    Foil-faced foam insulation installed on walls can be grounded easily (for example, if the wall is penetrated by a frost-proof sillcock).

    Airplanes aren't grounded.

    All of that said... there is no doubt that ungrounded aluminum foil can interfere with cell phone reception, because when I wrap my cell phone with aluminum foil, and place the cell phone on a wooden table, I am unable to make the phone ring.

  16. Bill Burke | | #16

    Low-e Glass and Cell Phone Reception
    I get the same question regarding use of windows that have low-e films that work as a radiant barrier. Here is the reply I put together to such an inquiry a few months ago. Comments on my response are welcomed. I simply tried to think through the issues and did a bit of online research.
    Bill Burke

    See the three attached documents that come from the California Air Resources Board (CARB). First, it looks like CARB is instituting requirements for solar control glass in automobiles! And they start with the 2012 model year! See http://www.arb.ca.gov/cc/cool-cars/cool-cars.htm. And for a reality check, also see http://www.snopes.com/politics/traffic/darkcars.asp. And related to that, see http://www.ppg.com/corporate/ideascapes/metalcoatings/products/coolmetal/Pages/default.aspx to understand that there are spectrally-selective coatings that can be applied to metal roofs (and to metal car body panels) that reflect the solar wavelengths we don’t see, helping to keep a roof or a car cooler than it would be if it absorbed all of the solar heat.

    What these documents show is that concerns have been raised about electromagnetic attenuation from spectrally-selective glass. However, CARB has conducted tests and come to the conclusion that the problem is limited. See document #1. #2 is a frequently asked questions document produced by CARB. And as document #3 makes clear, while there were concerns about ‘electromagnetic attenuation’, the far bigger concern was one of cost.

    To go back to your original question, nothing I see in these CARB documents suggests low-e glass causes problems with electronics inside a home or building. It does suggest there might be some loss of signal strength when sending a wireless signal through the glass. If you think back to the discussion of spectral-selectivity from the class, the question I immediately have is what are the wavelengths of the signals involved. Wireless devices broadcast at a variety of spectra. A mobile phone signal does need to go through the glass. A wi-fi signal goes to a wireless base station, which is going to be inside the house. So a question I have for you is what is it about your computer equipment that raises a concern? There’s nothing about low-e coatings that will disrupt operation of the equipment itself. And if you are sending a signal to a wireless router you shouldn’t encounter a problem. And since cell phone and wireless signals go through most walls, unless you’re planning an entirely glass house, signals should be able to pass through opaque walls.

    I don’t mean to downplay the potential problem. I can only tell you that I have not heard of mobile phone reception problems in new high rise buildings in San Francisco that are enclosed by large areas of spectrally-selective, low-e glass that don’t also occur in neighboring buildings without low-e glass. And I have replaced the windows in my home with windows containing spectrally-selective, low-e glass. I have had no problems whatsoever with my cell phone reception or with my wireless network. The problem for me has been that, depending upon device, my wireless network cannot penetrate through my bathroom – which has the original tilework from 1940. The wall assembly is wood stud, metal mesh, thick mortar, and finish tile. The router is in a bedroom. The bathroom is between that bedroom and our kitchen. My wife’s iPod Touch cannot receive a wireless signal in our kitchen. In our living room, which is farther from the router than the kitchen, but would not require the signal to pass through the bathroom walls, the iPod Touch does fine. My new iPad gets the signal in the kitchen just fine. Going back to the correlation and causality question, before I bought the iPad I assumed the cause was the lathe, mortar, and tile. Now that I know the iPad gets the same signal I don’t know what to think.

    If I were in your position, disruption from low-e glass would be low on my list of concerns. I can name office buildings that have data centers in them where all of the glass is spectrally-selective, low-e. Of course I’m not in your position! But if you want to eliminate low-e glass from your new home the way to do that is to limit the amount of glass on the east and west sides while making an effort to shade it as well as possible. With a roof overhang and/or window-specific shading devices, you could use uncoated glass on the south.

  17. Daniel Beideck | | #17

    Faraday Cage

    I'm not an expert, but have worked occasionally with the Faraday cages in MRI units. RF waves will completely mess up MRI imaging and even the door must be made part of the cage. I've tested the integrity of cages using a RF signal receiver, also known to the general public as a 'radio'! I go inside the room (being extremely careful to stay away from the strong magnetic field) and close the door. If I can pick up any radio station, we've got a leak. Just barely crack the door to break the seal, and the tunes come a blaring.

    All the windows and (non conducting) doors in a house would act as a similar break in the Faraday cage. However, that is not to say that materials in the walls and roof couldn't attenuate the signal somewhat and possibly make the difference between the phone working or not.

  18. Skip Harris | | #18

    empirical testing
    I built an office in our yard with foil-faced isocyanene between studs, rafters, and joists. Cell and wifi drop from 4 bars to one when I step through the door and 3g network drops to the point that pandora fails. Does anyone produce the iso between fiberglass or other non-metallic facing?

  19. GBA Editor
    Martin Holladay | | #19

    Response to Dustin Harris
    Dustin,
    Several manufacturers produce polyisocyanurate insulation with non-foil facings.

    These include:

    Atlas Rboard: One Atlas document describes the facing as "a coated fibrous facer."

    Firestone Iso 95+. This product has "black glass reinforced mat facers."

  20. Rhaud Macdonald | | #20

    cell phone reception
    Martin,
    Even good granite block foundations block cell phone reception!

  21. Andre Fauteux | | #21

    Reflecting and boosting toxic microwaves in homes is a bad idea
    Read this article by distinguished professor emeritus of engineering Frank Barnes of the University of Colorado, Boulder:
    Some Effects of Weak Magnetic Fields on Biological Systems: RF fields can change radical concentrations and cancer cell growth rates

    Barnes is a Fellow of the IEEE and the American Association for the Advancement of Science and has served as vice president, Publication Activities of the IEEE and as the chair of the IEEE Electron Devices Society.

    Also, see this reference:
    Building materials and electromagnetic radiation: The role of material and shape

    -- André Fauteux

    1. withColleen | | #23

      Thanks for sharing these references. I'd love to read this article from sciencedirect.com ... but, alas, $31 seems a bit steep for an article.

      1. Charlie Sullivan | | #25

        If you live near a university, some university libraries offer access to their subscriptions to in-person visitors, either to look at or photocopy paper copies, to view the pdf on their computers, or to access it from your own computer connected to their wifi. But policies vary--some are more open and friendly than others so if it's a long trip doing some research before visiting would be worthwhile.

        Another trick that may or may not work is to email the authors. They won't get a dime of the $31 and might enjoy hearing of your interest and be happy to send you a copy, which is usually allowed by the terms of the copyright agreement.

        1. withColleen | | #28

          Great tips, Charlie! Thank you!

  22. withColleen | | #22

    I'd love to see GreenBuildingAdvisor PROMOTE the use of grounded barriers using foil faced products and metal roofs as THE THING TO DO in order to turn homes into Faraday Cages as PROTECTION from RF pollution, a known carcinogen. The science is strong and consistent that Radio Frequency is adversely affecting all life on earth. The home needs to be made to be a sanctuary from this toxic exposure until legislation catches up with science and stops this madness.

    I WISH my home were a Faraday cage, living in Boston. Here, ambient Radio Frequency pollution continues to rise due to increased WiFi router strength (Verizon and Comcast placing additional transmitters in home routers to create "HotSpots" everywhere) AND Boston becoming a "Smart" city, placing transmitters all throughout the city on power poles. I have a RF meter and have measured the change.

    New codes should call for every wall in every room to be wired with high speed Ethernet, discouraging the use of wireless technologies in the home. It is not "Green" to use technologies that harm all life. The proliferation of frequency generating technology is out of hand and unnecessary, including entertainment equipment such as smart T.V.s and devices with transmitting remote controls other than the older IR device. Also the “Smart Home” products such as Nest have got to go and be replaced by wired options whose power and wiring and placement are built into the codes for new construction. In the utility closet we need to add cable or fiber entering the house into a router (without wifi) and Ethernet switch.

    There is no need to use a cell phone in the home when you can plug in a VOIP phone to your Ethernet and have FREE calling through your internet protocol. When Ethernet is placed in the right places throughout the home, Tablets and computers easily and conveniently connect via Ethernet, with a simple adapter, eliminating the need for WiFi.

    Dear GreenBuildingAdvisor, please catch up on the science and promote "wiring it"! Wireless Communication (Radio Frequency) is to our time what second hand smoke was to the 1960s-1990s. Let's not take over 30 years from scientific discovery to legislative action to stop the unnecessary exposure to this toxin too.

    The “Faraday Effect” of radiant barriers is a positive one! Keep RF out of the home.

    1. GBA Editor
      Martin Holladay | | #24

      Colleen,
      Few scientists agree with your analysis, which is unsupported by data. For more information on this issue, see "EMFs and Human Health."

      1. withColleen | | #26

        Hello Martin,
        Thank you for your response. It's nice to know comments are read by GBA!

        I did read your article and I noted that it was written 5 years ago. If that was the last time GBA looked at the issue, I would suggest looking again. I noticed that you had no quotes from biologists nor did you cite any studies. I did also follow the link and read the article on Huff Post about Smart Meters. I think it is important to note that neither author was a biologist but rather 1. a retired person from Lawrence Berkeley National Laboratory (Berkeley Lab) which is a Department of Energy (DOE) Office of Science lab managed by University of California (not an unbiased source, I think it is fair to say) and 2. a Laureate Professor of Mathematics, University of Newcastle, Australia.

        I feel a deep sense of caution when reading articles, such as this Huff Post article, that are dismissive and divisive; Inciting an attitude that implies that those who are raising concern are insane or on the fringe. This is not the way scientists behave, this is the way people who are afraid behave; this is the behavior of bullies.

        It is clear that I am listening to different scientists and different "experts" than what you have encountered thus far. What I can say is that it is always important to look at who funds the studies, as well as the parameters of the studies. Just like with tobacco dollars, there is a powerful industry here that will be altered when the unbiased science comes to light. Remember, the tobacco industry also had "science" showing that smoking didn't cause cancer. Note that “No Evidence of Harm” does not mean “Proven Safe”. It will take some time for it all to be ironed out and for our species to discover how much EMF exposure is actually safe, or how to utilize different frequencies that could be harmless or potentially helpful. Until then, it's the wild west.

        From what I understand from scientists such as Dr. Martin Pall and Dr. Devra Davis is that there IS data. Once just has to look for it. I also know of anecdotal evidence. I hope as Editor of GBA, you will look into this again. However, this time I suggest that you skip the snarky articles that enjoy lambasting those who are concerned, and go direct to the science written or lectured about by biologists where the focus is actually science.
        The joy of science is that we can keep learning more, and understand more deeply! It is my sincere hope that more of us have the courage to keep learning and that we are bold enough to follow and fund the science even if it damages our bottom line.

        Here, for example, is a cited article from 2016 that includes an interview with Dr. Devra Davis who studies environmental oncology. She wrote the book "Disconnect: The Truth About Cell Phone Radiation, What the Industry Is Doing to Hide It" https://amzn.to/2WWcziL
        https://articles.mercola.com/sites/articles/archive/2016/01/20/emf-controversy-exposed.aspx

        Again, I offer my sincere thanks for reading my comments.
        All the best, Colleen

        1. Trevor Lambert | | #27

          That was a whole lot of words. If there is evidence as you say, please just link us to it. You lost a lot of credibility by the fact your one link is to an article by Dr. Mercola, a confirmed quack.

          As for the book you mentioned by Devra Davis, I'll leave a link to a review of it here:
          https://sciencebasedmedicine.org/a-disconnect-between-cell-phone-fears-and-science/

          1. withColleen | | #29

            Hi Trevor,
            Check out presentations by Dr. Martin Pall:
            https://www.youtube.com/results?search_query=dr.+martin+pall

            There's quite a bit here: https://bioinitiative.org/research-summaries/
            Also, this is a bit of a maze but, there are some good links to more recent studies here: http://www.oscillatorium.com/

            The review you linked does suggest that all of Dr. Davis' work is wrong but doesn't do a great job of citing these claims with modern research, unfortunately. Dr. Martin Pall does address the physics questions and his explanation that RF exposure from the communication hz causes intra-cellular calcium as the mechanism for damage, is truly staggering. There continues to be replicated studies apart from Dr. Davis' work. (links above)

            At the very least we should be applying the cautionary principle here. I know it's inconvenient that we likely need to reduce the use of the communication frequencies in use, but what's the alternative? Shall we keep drumming up reasons to discredit scientists who discover inconvenient evidence? Shall we keep our heads in the sand? I have a family and I care about our future, our freedom, our health, our planet. I'm hopeful that more will join in expressing their concern.

    2. Kenneth Gartner | | #31

      What an excellent series of rational statements, WithColleen!

      Most folks on this forum are going to reject this info no matter how rational your discussion, no matter how many scientific papers you show them. I have tried and failed as well. Building codes are compromises, and glacially responsive to changing conditions.

      The points you raised are all valid. Having CATn (ethernet) cabling when a house is being built would ensure that one could run entirely without WIFI (except for occasional periods needed for must-have WIFI-only gadgets such as a Kindle) for basic creature comforts, but the tide is toward an 'internet of things' that is rather WIFI-centric (sensors, meters and devices, all) so the ethernet-only approach will be a viable one. This is how we run here at our house (see my other reply to this thread). For flexibility, one can inexpensively deploy ethernet-over-powerline devices to sprinkle a few ethernets into places they do not exist now, at the expense of adding harmonics to a few of the circuit wiring paths (aka, Dirty Electricity), still bio-affecting, but less so than the WIFI signals they replace.

      The one item i did not see you mention, in your otherwise inspiring commentary, is that of the electronic meters from the gas/electric utilities. We have a 'simple' ITron C1SR6 AMR meter attached to the house, as they will no longer install analog in MA new construction for either love or money. This AMR meter has a nearly constant 900 MHz signal being broadcast throughout the neighborhood (as part of their mesh network, one imagines), with large pulses every 45 seconds and even longer broadcasts every three minutes as measured by my RF meters. We were able to diminish it a lot with a mesh cage around the glass front, but the signal is so powerful that it still impinges into the house and renders large areas of the house uninhabitable/untraversable for our electrosensitive occupant. I am still figuring out my options to overcome this beast, as the normal 'opt-out' path will replace with a meter that does not send out RF blasts (for $132 surcharge per year) yet still produces huge DE. Not an acceptable tradeoff. If I were to do it again, I may have installed some specific metal sheeting under the exterior sheathing, where the meter would ultimately be placed, to reflect the RF into the street where it belongs.

      Thanks for mentioning Dr. Pall and the BioInitiative 2012 -- that shows several hundred scientific papers right there. Your might want to look into Magda Havas (Toronto), or some of the old timers Robert Becker/Andrew Marino whose decades of research has stood the test of time and been replicated many times now.

      Please do not be dispirited about the naysayers, even on quality forums such as GBA. There is too much cognitive dissonance for most people to rationalize how much harm they inadvertently might be doing to themselves, their children and the frail as they promote the latest whizbang WIFI-connected device or LED/CFL lighting or Solar Panels on house roofs or other 'green' ideas that eventually might trade off long term health for short term money savings. Having a rational discussion about such things would seem a natural first step, but don't hold your breath ;-)

      Your positive, can-do attitude is energizing. Great job pointing out the bias of authors of the snarky, divisive hit pieces. The people you want to seek out might be Building Biologists, who actually are completely focused on human health and comfort in the house and workplace, and so have generally much more aggressive safety standards than you will find reflected in the building codes, the FCC, the FDA, the NEC/FPGA, the W.H.O. and other regulatory bodies.

  23. Kenneth Gartner | | #30

    Our personal experience is that the foil-based polyiso DOES attenuate frequencies associated with both WIFI (2.5GHz) and Cell (1-3 GHz). Our house was completely surrounded with a double layer of 2 inch polyiso panels, each having foil on both sides. This was the same for the roof as well as the walls. There is a galvanized metal roof. Concrete slab (no basement). The windows are PVC with double pane/triple glazed and plastic mesh screens, otherwise nothing special. I noticed the diminished signal during the housebuilding process, after the foil-backed foam went on and before the metal roof was installed. [interim build photo attached, showing the kind of foam I am talking about]

    With this configuration, we will not see the neighbor's wifi signal inside. even though the signal is seen on the outside porches. Similarly, the cell tower signal is so diminished that I cannot reliably connect to 4G unless the cell phone is at the window when inside, though there is adequate service when outside on the porches.

    I have used several RF meters to quantify this and indeed the inside versus outside RF readings show the signal has been diminished significantly.

    For us, this is an unexpected blessing, since we use neither WIFI nor cell inside due to electromagnetic sensitive occupant. It is a minor inconvenience because we can use a landline for occasional calls and have google phone number forwarded to an ethernet-based phone gadget, so only dealing with text messages is problematic.

    On the flip side, a cell phone in the house, but not on FLIGHT mode (ie, with its RF signals still active) will aggressively try to reach a cell tower or distant wifi and the amplified signal will make the inside quite intolerable for the electromagnetically sensitive occupant. And drain their batteries quickly in so doing. Thus, we do ask our guests to both take off their shoes and disable their devices before coming in for an extended visit.

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