musingsheader image
Helpful? 1

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

Posted on Jul 27 2012 by Martin Holladay, GBA Advisor

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 result in some reflected heat and thus a savings in A/C costs so I said yes. I have not seen any saving in the A/C cost, but I did realize a total inability to use cell phones in my home. … The signal was still poor in the house and Verizon said that the radiant shield was like a Faraday shield and that it was blocking the cellular signals.” (Invented by Michael Faraday in 1836, a Faraday shield is a cage or enclosure of conductive material used to block electrical fields.)

Johnson continued, “I ended up purchasing their in-home amplifier and it works pretty well. Verizon said that they were getting similar complaints from new-home buyers where the contractor had installed the radiant barrier on the new home.”

A similar complaint was posted on a home-advice web site by someone identified only as Mary: “We built a home and have Tech Shield Radiant Barrier in the attic. The problem is that we are only able to use our cellphones in certain areas of the house.”

In the same vein, a GBAGreenBuildingAdvisor.com reader named John Link posted this comment on GBA: “I recently built a garage using foil-faced foam. My cell phone completely dies inside.”

What do the manufacturers of foil-faced foam say?

I sought some answers from representatives of three manufacturers of foil-faced building products: Dow Building Solutions (the manufacturer of Thermax foil-faced polyisocyanurate), Louisiana-Pacific (the manufacturer of TechShield radiant barrier roof sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen. ), and Johns Manville (the manufacturer of a brand of foil-faced polyisocyanurate called AP Foil-Faced).

The spokesperson from Dow Building Solutions, Gary Parsons, was categorical. “Thermax insulation with the aluminum facers has been used in numerous building exteriors, interiors, and roof systems since 1969,” said Parsons. “Dow has not experienced any issue with regards to radio frequency or cellular interference from using Thermax on interior, exterior or roof systems of buildings.”

The representatives of Louisiana-Pacific and Johns Manville were more nuanced. “There are plenty of documented cases where people report diminished reception in houses with aluminum siding and metal roofs,” said Robert Palardy, manager of technology at Louisiana-Pacific. “With radiant barriers, I don’t know if it is that well documented. I have heard of people reporting those problems, but there are many factors that can affect cell phone reception. In general, metal can affect the transmission of radio waves. 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 or a noticeable effect.”

The response I received from J.R. Babineau, a research associate with Johns Manville, echoed some of the points made by Palardy. “I have never encountered a direct complaint about cell phone problems myself, and our tech services guys have had no complaints along those lines,” said Babineau. “I couldn’t imagine that there would ever really be a problem. But I did a web search, and I see that some of the radiant barrier guys have encountered it. My educational background is in applied physics, and I know about Faraday cages. That is how you create an EM-shielded space — you use some sort of metal, and you make it as closed up and electrically conductive as possible. With a building, though, the same effect shouldn’t really happen, because you have windows and doors. To make a good shield — even if it is by accident — you need circuit continuity.”

What do radiant barrier installers say?

Most radiant barrier distributors and installers admit that their products may cause problems with cell-phone reception; however, they usually emphasize the problems are rare.

According to a web page maintained by AtticFoil.com, a radiant barrier distributor, “The thickness and the amount of the aluminum being used (surface area) can determine whether or not it will completely block radio waves to/from your cell phone. … AtticFoil radiant barrier … is a thin layer and is only covering the roof of your home (generally around 20-35% of your total surface area). Your home still has four walls that radio waves can travel seamlessly through to provide a signal for your cell phone. … The only cases where we’ve heard of signal transmission problems arising are where the cell phone or particular area had a weak signal to start with; beyond that there have been no reported issues.”

A web page maintained by Solar Attic Blanket, a distributor of radiant barriers, advises homeowners to perform a test if they are worried about potential cell-phone problems: “Usually there is no impact to cell phone reception following installation. An easy way to test is to get a free sample [of radiant barrier material]. Cover your cell phone with the radiant barrier foil and call it. If it rings, then the phone should work fine after installing the radiant barrier.”

Of course, this type of test raises another question: is this method actually predictive of conditions that occur after foil is installed in an attic?

What do the cell phone companies say?

As noted earlier, a T-Mobile spokesperson told me that foil-faced building materials can block cell phone signals. Tom Pica, executive director of Corporate Communications at Verizon Wireless, was less certain. “I don’t know if it is a major problem,” said Pica. “It’s true that certain building surfaces can affect the ability of a signal to penetrate a building.”

When I contacted the Cellular Telecommunications Industry Association (CTIA), a lobbying group for the cell phone industry, I wasn’t able to get a CTIA representative to make a statement on the record. However, a CTIA employee who asked to remain unidentified told me, “Technically the answer is that foil-faced barriers can impede signals, but the extent to which it happens depends on the nature of the insulation and the number of gaps like windows and doors.”

What does David Yarbrough say?

One of the most respected insulation experts in the country is David Yarbrough, a research engineer at R & D Services in Cookeville, Tennessee. Responding to my e-mailed inquiry, Yarbrough wrote, “The question about radiant barriers or foil-based reflective insulation interfering with electronic signals (cell phones, for example) has been discussed for many years. I am not aware of any actual signal strength measurements. The effect seems to be mostly anecdotal. Logic suggests some shielding effect. The key question is the signal strength with and without an attic radiant barrier in place. … Whether or not the metal shielding effect has an impact on reception depends on the signal strength in the area of interest and the sensitivity of the cell phone (or electronic device). A few years ago I tried to make measurements with a signal-strength meter. My meter was not sensitive enough to see any effect. This is a complicated issue without much data.”

Pulling it all together

I’ll attempt to integrate the information I gathered into a preliminary conclusion: Foil-faced building materials can probably interfere with cell phone reception, but only in homes that have relatively weak cell phone reception to begin with. Most people who live in homes with foil-faced building materials do not have cell phone reception problems.

If you’re one of the homeowners who is facing this problem, what’s the solution? Some installers of radiant barriers urge customers with cell-phone reception problems to install a cell phone signal booster. These devices generally start at about $250; they’re available from some cell phone companies as well as independent manufacturers, most notably Wilson Electronics.

Although these devices can be easily purchased over the internet, their use falls into a legal gray area. Unless you buy your device directly from your cell-phone service provider, the use of a cell phone signal booster is frowned on by most cell-phone companies. The regulatory issues are complicated; if you’re interested in more details, a good resource is a New York Times article, “Cellphone Carriers Try to Control Signal Boosters”. Legal or not, the devices apparently work.

Last week’s blog: “Alaskan Glaciers Are Rapidly Melting.”

Click here to follow Martin Holladay on Twitter.


Tags: , , , ,

Image Credits:

  1. Louisiana-Pacific
1.
Fri, 07/27/2012 - 07:35

Edited Fri, 07/27/2012 - 07:36.

My DIY test results
by Daniel Morrison

Helpful? 0

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.
Fri, 07/27/2012 - 08:19

Moisture and breathing issues
by aj builder, Upstate NY Zone 6a

Helpful? 0

Moisture and breathing issues may arise Dan


3.
Fri, 07/27/2012 - 08:38

My test results
by Martin Holladay, GBA Advisor

Helpful? 0

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.
Fri, 07/27/2012 - 09:04

Wall thickness
by Dan Kolbert

Helpful? 0

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.
Fri, 07/27/2012 - 09:58

Metal Roofs
by Jeff Haines

Helpful? 0

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.
Fri, 07/27/2012 - 10:08

Response to Jeff Haines
by Martin Holladay, GBA Advisor

Helpful? 0

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.
Fri, 07/27/2012 - 14:56

faraday cage
by bob coleman

Helpful? 0

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.
Fri, 07/27/2012 - 15:19

Wireless routers affected, too?
by Dick Russell

Helpful? 0

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.
Fri, 07/27/2012 - 16:07

Response to Daniel Morrison
by Bill Costain

Helpful? 0

"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.
Fri, 07/27/2012 - 19:03

How come I cannot hear my
by Keith Gustafson

Helpful? 0

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.
Sat, 07/28/2012 - 11:19

Next great idea
by Doug McEvers

Helpful? 0

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


12.
Sun, 07/29/2012 - 12:50

Edited Sun, 07/29/2012 - 12:52.

If still wrapped, said
by aj builder, Upstate NY Zone 6a

Helpful? -2

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.
Mon, 07/30/2012 - 16:37

Edited Mon, 07/30/2012 - 16:38.

My anecdotal 2 cents
by ken dupuis

Helpful? 1

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.
Mon, 08/06/2012 - 14:36

What about aircraft hulls?
by Mark Walter

Helpful? 0

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.
Mon, 08/06/2012 - 15:00

Edited Mon, 08/06/2012 - 15:03.

Response to Mark Walter
by Martin Holladay, GBA Advisor

Helpful? 0

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.
Thu, 08/09/2012 - 15:11

Low-e Glass and Cell Phone Reception
by Bill Burke

Helpful? 0

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... 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.
Mon, 08/13/2012 - 11:05

Faraday Cage
by Daniel Beideck

Helpful? 0

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.
Mon, 10/15/2012 - 18:22

Edited Mon, 10/15/2012 - 18:23.

empirical testing
by Dustin Harris

Helpful? 0

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.
Tue, 10/16/2012 - 03:53

Response to Dustin Harris
by Martin Holladay, GBA Advisor

Helpful? 0

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.
Sat, 11/03/2012 - 00:33

cell phone reception
by Rhaud Macdonald

Helpful? 0

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


Register for a free account and join the conversation


Get a free account and join the conversation!
Become a GBA PRO!