Eric Nelson, an architect with ties to both the U.S. and Switzerland, is looking for someone in North America willing to take a leap of faith with his novel insulation and cladding system. So far, there are no takers.

Nelson’s Solar Activated Façade (SAF) was recently named one of the greatest home innovations of the year by Popular Science magazine, but it’s a good bet that few builders or designers have ever heard of it, much less specified it for a new house. Developed in Switzerland in the late 1990s by an architect named Guiseppe Fent, SAF combines wood, glass and an air space in a wall assembly.

According to Nelson, a south-facing SAF that is just 9 1/2 inches thick will have an average “effective” R-value of 120 to 150 over the course of a heating season when installed on a wood-framed house in Boston, Massachusetts.

But Nelson’s use of the phrase “effective R-value” on his company’s website will raise red flags for many energy experts. “Effective R-value” is a metric with no scientific definition, and it has been associated with exaggerated claims in the past. Measured according to the way R-values must be reported in the U.S., the wall with an “effective R-value” of 150 would have a whole-wall R-value of about R-21. (For a discussion of questionable uses of the phrase “effective R-value,” see All About Thermal Mass.)

In the Boston example, the touted thermal performance wouldn’t be as eye-popping on walls facing a direction other than south, but according to Nelson, it would still be higher than anything builders can currently get their hands on. Nelson says that SAF has been “repeatedly tested” at Empa Switzerland (Swiss Federal Laboratories for Materials Science and Technology) and other labs.

In addition to its high “effective R-values,” the cladding needs little maintenance because it’s made mostly from glass, and the assembly should last 50 years or more. Nelson says those factors, combined with the energy it saves, give SAF a lower lifetime cost than a conventional exterior thermal insulation composite systems, also known as ETICS. (The cladding system known in Europe as ETICS is known in the U.S. as “exterior insulation and finish system,” or EIFS).

There are just two problems: it’s expensive, and Nelson has yet to find a customer on this side of the Atlantic willing to give it a try.

How the wall assembly works

The SAF is applied over a structural wall in new construction — a framed wood wall or a wall made of concrete block, for example — or over an existing wall when it’s used in an energy retrofit. It consists of a milled wooden louver called the “absorber,” an air gap, and a sheet of tempered glass, which together makes a layer 2 1/2 inches thick.

The fins are milled into the wood layer at an angle, which regulates how much solar energy the wood can absorb. In winter, when the angle of the sun is low, sunlight can reach the core of the absorber to heat it up during the day. After sunset, the solar-heated buffer cools down, releasing the heat it stored during the day and reducing heat loss through the wall. In summer, when the sun angle is higher, the glass reflects some of the solar energy; the layer of air behind the glass warms and rises, carrying heat up and out of the building while the downward angle of the louvers prevents sunlight from reaching the core of the wood layer (see Image #2, below).

The wall can be installed either as preassembled units or on site, Nelson says, although the preferred method now is to prefabricate panels off site.

According to Nelson, a major advantage of the assembly is that it produces very high “effective R-values” with minimal wall thickness. One example posted at his web site shows a framed 2×6 wall filled with rock wool insulation, 3/4-inch wood sheathing, and 1/2-inch gypsum drywall, clad with a SAF: the total wall thickness is 9 1/4 inches.

On a south-facing wall, the R-value would have an “effective R-value” of 150. On east and west walls, the “effective R-value” averages 95, and on the north wall the average over a heating season is 44. Thermal performance changes as conditions change.

“Our numbers are dynamic,” Nelson said in a telephone interview. “It’s a dynamic R-value. It’s actually different from hour to hour, day to day, month to month. For simplicity reasons we average. Throughout the winter period, we can produce an average [‘effective’] R-value of 150. Sometimes we may be at R-80, sometimes at R-120, sometimes at R-200.”

How the numbers were derived

The tests, carried out under contract at Empa Switzerland, measured heat flow through a sample wall section over a month-long period simulating winter, and a two-week span simulating summer conditions. Sensors to measure heat were placed throughout the cross section, beginning outside the glass to measure outside air temperatures and spaced at intervals to the interior surface.

A second purpose for the testing was to check whether the company’s computer software could accurately predict measured performance. Nelson described the tests in general terms, but said the reports themselves are proprietary.

“We can predict the U-values/R-values for any climate and for any orientation of the façade,” he said.

Are the “effective R-values” too good to be believed?

“Actually, it is just as you say,” Nelson said. “Those are mind-boggling numbers and it’s hard to wrap your mind around it. It doesn’t help me at times because it just creates too much doubt.

“I’ve had a lot of interested people, and they’re all amazed,” he continued. “They say, ‘Wow, this is absolutely gorgeous, and high performance,’ and everything but just trying to nail that first project is not all that easy. I saw this in Switzerland, too. You can be the subject of a lot of talk, but people are unsure about it because they are not used to thinking that way. You just stick with what you know — architects as well as clients…This is difficult, I think, because people just don’t understand it.”

[GBA contacted both the Oak Ridge National Laboratory and the National Renewable Energy Laboratory to ask whether any scientists there might comment on the SAF assembly. NREL said no one on its staff was familiar with the technology; ORNL has yet to respond.]

Plan on high cost

Nelson said a SAF would cost up to twice as much as an Exterior Thermal Insulation Composite System (ETICS), although he wouldn’t say exactly how much. In a life-cycle cost analysis conducted in Switzerland, and assuming the wall lasted for 50 years, he said the cost would actually be one-third lower than ETICS when energy savings and the cost of disposal were figured in.

“One main advantage is you can have much thinner walls to achieve high performance, so you can reduce the thickness of your walls tremendously,” Nelson said.

Where square footage is valuable and setbacks are very tight, he added, getting high performance without sacrificing too much floor area could outweigh higher initial costs, he said, although that probably would not be the case in rural areas where property prices and housing densities are lower.

Nelson says that the assembly has included textured solar glass to increase the amount of solar energy that passes through to the wood louver, but he’s weighing a switch to tempered float glass because it’s less expensive. Performance “barely changes” with the substitution.

Another incentive could be the addition of photovoltaic cells in the assembly, a feature Nelson says is the subject of a patent application.

Still looking for his first customer

Nelson said he grew up in Switzerland but eventually moved to Florida, where he earned a master’s degree in marine science. He worked for the U.S. Geologic Survey, then switched gears and earned a master’s degree in architecture.

“I quickly realized that architecture, green building, at the time was so backward, especially in Florida, of course,” Nelson said. “I decided to go back to Switzerland where I ran into [Guiseppe Fent] by total coincidence. I thought he would be a provincial architect. It turned out to be he was quite an innovative, thinking-out-of-the-box kind of person.”

Fent, Nelson said, had developed SAF in the 1990s. It was installed on the first house in 1999 and has since been used on 100 or so projects around Switzerland, sold through Fent’s Lucido Solar company.

Nelson called Fent a “self-made, innovative man who has pushed the envelope in green building.”

“He’s been a true pioneer when it came to green buildings,” Nelson said. “The reason why he developed this system was because he just couldn’t find any suitable materials that were really green and suited his ambitions. So he created this and became his own best client.”

Nelson went to work for Fent’s company. Eventually, Fent approach Nelson and offered him rights to the SAF patent in North America. Since then, Nelson has been building a network of contacts, many of them in the Boston area, while he tries to drum up business. He was close to landing a job in Tennessee, and has been talking with a Minneapolis architect who’s apparently interested in using SAF on his own house. But so far, SAF is a product in search of its first North American customer.

“I’ve been kind of stirring the pot, building my website, building my business plan, market research and all that, step by step,” Nelson said. “We have been close to projects…”