©2013 Green Building Advisor. From The Taunton Press, Inc., publisher of Fine Homebuilding Magazine.
If you’re shopping for a garage door, the door’s energy performance may not matter — especially if you don’t heat your garage. However, there are a few reasons why you might be looking for a well-insulated, draft-free garage door:
So, how do you tell a high-performance garage door from a lemon?
“We sell high R-valueMeasure of resistance to heat flow; the higher the R-value, the lower the heat loss. The inverse of U-factor.
Many garage-door manufacturers advertise the R-values of their doors:
Unfortunately, these advertised R-values are almost meaningless.
Advertised R-values are inaccurate, irrelevant — or both
To determine the thermal performance of a garage door, you need to know two things:
The R-values that are trumpeted by garage-door manufacturers are measured at the center of one of the door panels. No manufacturer, as far as I can determine, reports the R-value of the entire door assembly (including the panel edges, the seams between panels, and the perimeter of the door) in their promotional materials. Moreover, manufacturers’ reported R-values tell us nothing about air leakage.
Most garage-door manufacturers are reluctant to share actual laboratory reports showing the results of R-value testing. When I asked Mike Willstead, a technical representative for Raynor, if I could see a copy of Raynor’s test results, he suggested I send him an e-mail. He later e-mailed his response: “I apologize if I misled you. I was informed that this is proprietary information that will not be disclosed.”
The window industry does a much better job
More than a decade ago, responsible window manufacturers realized that the reputation of their industry was being damaged by misleading R-value and U-factor claims. (U-factor is the inverse of R-value; in other words, U=1/R and R=1/U). To address these problems, industry leaders developed a method for testing and reporting whole-window U-factors. The U-factor reported on an NFRC label accurately describes the U-factor of the entire window, including the sash frame and the window frame — not just the center-of-glass U-factor.
When it comes to accurate reporting of U-factors or R-values, however, the garage door industry is years behind the window industry.
There’s nothing to prevent garage-door manufacturers from using the NFRC testing and labeling protocol — a protocol that yields a more honest and useful result than the center-of-panel numbers trumpeted by garage-door marketers. Alternatively, garage-door manufacturers could use the voluntary consensus standard (ANSIAmerican National Standards Institute. National nonprofit membership organization that coordinates development of national consensus standards. Accreditation by ANSI signifies that the procedures used meet the Institute’s essential requirements for openness, balance, consensus, and due process. /DASMA 105) for reporting whole-door U-factors adopted by the Door and Access System Manufacturers Association (DASMA). A technical data sheet (DASMA TDS #163) describes this testing protocol, dubbed the “tested installed door” protocol by DASMA.
“For marketing purposes, the garage door people get a measurement on the center of panel,” said David Yarbrough, a research engineer and insulation expert at R&D Services in Cookeville, Tennessee. “The overall R-value of the entire door might be quite a bit less — in extreme cases, it may be half — of the R-value of the center of the panel. Not everyone approves of this kind of marketing. It’s been a hot debate in recent years.”
In fact, the percentage turns out to be much less than half.
Actual R-values are one-third the advertised values
Although it’s hard to obtain actual test results that report the whole-door U-factors of “tested installed doors,” I managed to obtain one report on a garage door from Clopay, and another on a garage door from Overhead Door.
Clopay provided test results for their model 3720 five-panel garage door. According to Mischel Schonberg, Clopay’s public relations manager, the door is insulated with 2 inches of polyurethane foam. Schonberg wrote, “This model is the commercial version of our residential model 9200 and has the same construction.”
While Clopay advertises that the 9200 door is R-17.2 — presumably, a claim based on a center-of-panel measurement — the test report for the installed door shows R-6.14.
While Overhead Door advertises that their model 494/495 Thermacore door has an R-value of 17.5 — a claim that, like competitors’ claims, is presumably based on a center-of-panel measurement — the test report for the installed door shows a U-factor of 0.16, equivalent to R-6.25.
Based on the only two test reports that I was able to track down, it seems logical to conclude that the R-value of a garage door is about one-third of the R-value claimed in a manufacturer’s brochure.
All over the map
Mike Thoman, the director of thermal testing and simulation at Architectural Testing Incorporated, a Pennsylvania laboratory, has tested many garage doors.
“The assembly R-values are not going to be nearly as good as the R-value of the material would indicate,” Thoman told me recently. “When you compare the assembly R-value to the material R-value, the percentages are all over the map. The percentage is a function of how the joints in the panels are made, and whether any attempt was made to provide for thermal breaks at panel edges — a lot of different things. Some products have a lot of insulation in the panel but have everything else wrong. We’ve also seen doors that do everything right. There’s really a wide, wide range.”
Are the reported R-values even accurate?
There’s another potential problem with the R-values reported by garage-door manufacturers: even if one accepts the fact that the advertised R-values represent center-of-panel values rather than whole-door values, the numbers are still higher than most insulation experts believe are possible.
Several manufacturers report that their polyurethane-insulated door panels have R-values between R-8.6 and R-9.0 per inch — values that are highly unlikely if not technically impossible, even for the center of a door panel.
“The R-value of polyurethane decreases with age,” said Yarbrough. “When it is absolutely fresh you might get R-7.5 per inch, but a realistic aged R-value would be lower — perhaps about R-6.5 per inch would be on the high end. I’m not sure I can explain these reported test results. I have seen labs make mistakes before. I think it’s an error.”
One garage-door distributor who doubts the accuracy of manufacturer’s R-value claims is Bill Feder, the president of Door Services Incorporated of Portland, Maine. On his own initiative, Feder sent a garage-door panel (Overhead Door model 194) to Yarbrough’s lab, R&D Services. The ASTMAmerican Society for Testing and Materials. Not-for-profit international standards organization that provides a forum for the development and publication of voluntary technical standards for materials, products, systems, and services. Originally the American Society for Testing and Materials. C518 test conducted by Yarbrough came up with a value of only R-7.83 for the 1 3/8-inch-thick panel. Yet Overhead Door advertises that the door is R-12.76 — or R-9.28 per inch.
Feder’s R-value challenge
“If anyone calls me about a door, I tell them about my R-value challenge,” Feder told me. “I will give anyone a check for $250 if they can bring in a document that shows that a 1 3/8-inch-thick garage door has an R-value of 12. They can’t do it.”
Unfortunately, Feder’s admirable challenge has not yet shamed the garage-door industry into correcting the numerous exaggerations in their product specifications.
What about air leakage?
If the day ever comes when garage-door manufacturers follow the path blazed by their more honest brothers and sisters in the window industry — that is, if they ever decide to report whole-door U-factors or whole-door R-values — an important piece of the door-rating puzzle will still be missing. The reason: when it comes to the thermal performance of garage doors, air leakage matters much more than R-value.
“Garage doors are so leaky that they are difficult to test,” Thoman said. “Their leaks exceed the capabilities of the available testing apparatus.”
When he needed to buy a garage door for his own house, Thoman ignored advertised R-values. “I find it almost offensive that garage-door manufacturers even publish the R-value of the insulation material,” Thoman told me. “I hate it when I see that, because it’s not a representation of the door’s performance. Air leakage is a much more important issue than the R-value of the door.”
The bottom line
Although some garage-door manufacturers have measured the whole-door U-factor and air-leakage characteristics of their doors, most won’t release the data. Until they do, purchasers of garage doors have to select their doors based on anecdotes.
If any readers have identified a garage door that limits air leakage, please tell us the brand. When you post your garage door recommendations, provide your full name — so we can tell the garage-door salespeople from the architects, builders, and homeowners.
“I tell customers that the R-value of the door should be the last thing you should think about,” Bill Feder told me. “Instead, look at the seals and the hardware. On my own garage I just have a raised-panel cedar door.”
Last week’s blog: “It’s OK to Skimp On Insulation, Icynene Says.”