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.”
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 GBA 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 sheathing), 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 WeBoost.
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.
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