In a development outside Knoxville, Tenn., four houses are being constructed that will put to the test much of what’s new in energy-saving products for the roof and home.

Roofing assemblies will be tested for energy efficiency on homes being built by the ZEBRAlliance (Zero Energy Building Research Alliance) near Knoxville, TN.

In a development outside Knoxville, Tenn., four houses are being constructed that will put to the test much of what’s new in energy-saving products for the roof and home.

Each house has approximately 400 sensors that will collect data for a period of two years, in order to provide valuable insights about how well products stack up to their energy-saving claims and work together to achieve a targeted 50 percent reduction in energy use.

On this basis alone, “it’s a ground-breaking project,” said Dr. Bill Miller, a Senior Research Engineer at Oak Ridge National Laboratory, and project manager of the team that came together as the ZEBRAlliance (Zero Energy Building Research Alliance) to build the test homes.

Team members also include local builder Schaad Construction and architects Barber McMurry Inc., with funding from the Department of Energy and Tennessee Valley Authority.

Dr. Miller said while people have set up demo homes and tested a roof or a window, up to now, “no one has ever taken the initiative of documenting how it all merges together.”

ZEBRAlliance has identified the roof as a hot spot for energy savings.

“It’s the first line of defense against the environment and sees the greatest extremes of temperature,” Miller said.

He points out that, along with attics, the roof accounts for around 20 percent of energy loss in the average home. So there’s huge scope for improvement, and manufacturers are keen to show how well their products can perform to help reach that 50 percent energy reduction goal, he added.

A new synthetic underlayment for metal roofs, DELTA-TRELA is being used in test homes being constructed near Knoxville,TN. Vapor-permeable and waterproof, it provides an provides an escape route for moisture from in-house humidity and any outside sources, and ventilates and dries the roof assembly.

Eager Participant
One eager participant is Cosella-Dorken Products Inc., for whom the project is acting as a virtual launch pad for a new underlayment for metal roofs. Although DELTA-TRELA roof underlayment has been used in Europe for over 10 years, it is only now being introduced to North America in a move timed to coincide with the drive for greater energy efficiencies by home builders, according to Marcus Jablonka, C-D’s Vice President of R&D and Production.

Globe-trotting U. S. architects also found the unusual new product in Europe, sparking demand here. Frank Gehry, for example, saw it in Germany and has specified it for use behind the stainless steel plates that make up the façade of the new Lou Ruvo Center for Brain Health in Las Vegas - a dramatic, undulating building that mimics the contours of the brain.

Consisting of a springy, dimpled fiber mat adhered to a vapor permeable base sheet, DELTA-TRELA creates an air gap between the metal roof and roof boards that deals effectively with excess moisture, a problem that typically plagues airtight, energy-efficient homes. As vapor rises, it usually finds its way into roof insulation and deck boards. TRELA wicks away the moisture to dry and ventilate the deck. At the same time, it drains off any water that condenses on the underside of the roof or finds its way in from outside.

“The air gap is ventilated to the outside at the ridge so that hot air can escape to reduce the temperature in the cavity,” Jablonka said. “When the sun is beating down, less heat goes into the house, so the underlayment also contributes to energy saving.”

He added that although it’s not an energy-saving feature, TRELA also reduces rainfall noise by up to 15 decibel and eliminates noise made by the metal panels when they heat up and expand, since it acts as a slip layer to allow tension-free expansion.”

“With a painted metal roof right on top of a structural insulated panel and OSB, the temperature can get as high as 180 F degrees in summer,” he added.

After belatedly hearing about the new product, the ZEBRAlliance team made the decision to rip off the 30-pound roofing felt originally installed over an OSB deck on one of the test homes and replace it with TRELA. The house was then completed with a standing seam panel roof in galvanized steel with infrared reflective paint, and the whole roof assembly instrumented with sensors that will measure the temperature and moisture in and beneath the roof deck and the relative humidity in the air gap created by the TRELA. Heat flux sensors were installed to capture data on how much heat makes it through the roof.

Line Collecting Data

All four houses will be up on line collecting data in December. “Some monitoring starts this July with test data going to the mainframe at Oak Ridge,” Jablonka said. “Although full reports are one year out, we could have an interim report in about six months.”

The analysis of the monitored thermal and moisture data will be spearheaded by Dr. Achilles Karagiozis, a Distinguished Research Engineer at ORNL.

Occupant loads, that is, the amount of energy and moisture contributed by human activity, will be simulated through the control-directed operation of appliances, lights, showers and the like, so that the data collected is based on real-life use, not the static conditions of an unoccupied home.

In the drive for energy and environmental conservation, specialized roof underlayments will play an increasingly important role, Jablonka maintains. He points out that they represent one of the best and least expensive methods for getting rid of excess moisture. “There’s no sense putting an expensive, durable and energy-efficient roof cladding on a building if the roof structure is not properly protected against moisture damage that may lead to premature failure,” he observes. As yet, however, there is not a great deal of independent data on how new underlayments such as TRELA perform to reduce energy use in the home. The ZEBRAlliance project should help fill that gap, since a second house in the test group equipped with the same roof assembly minus a roof underlayment will make side-by-side comparisons possible.

All four ZEBRAlliance homes feature a different envelope strategy. At 2,600 and 3,700 square feet, they are in pairs identical in footprint and orientation to the sun. The two remaining homes use varying roofing techniques. One features a stone-coated metal roof on double TechShield, a Louisiana Pacific product, with a Sharkskin roof underlayment. Light reflective asphalt shingles over TechShield and plywood were employed for the last roof assembly.

Four test homes being constructed near Knoxville TN will collect data on the performance of new energy saving and advanced products, such as DELTA-TRELA, above, a synthetic underlayment for metal roofs.

Building Green

The homes should provide some helpful findings for roofers and builders who are faced with a confusing multitude of techniques and products with which to build green. Overall, roofing technology has made great strides. However, nearly all improved products achieve energy conservation by passive means. The question that naturally arises is, could the roof also actively contribute to heat recovery?

According to Dr. Miller, to date the reason why heat recovery hasn’t been exploited is because of the complexity of roof structures. However, prospects are ripe for new ideas in this area. He especially likes the idea of using the roof as a solar collector, and is currently collaborating with engineer Victor Zaderej to build a home in Oregon, IL that explores this concept. “There is a lot of heat up there that can be used to provide free heat for the house,” he said. “If channeled correctly, it could definitely be of value.”