Pushing and Predicting the Envelope

Energy Efficiency

From large-scale public facilities such as convention centers and airport terminals, to medical centers, retail stores and multifamily residences, buildings represent the largest energy consuming sector in our economy. And, heating and cooling these buildings consumes the greatest amount of energy

Tom Robertson, business unit manager, Atlas Roofing Corp., Atlanta, asserts that not only must the building envelope be high efficiency once built, it should also have lower initial investment and building costs, while still be a structure that can last. He predicts to address rising concerns with cost and longevity, there are several unique aspects of building design that architects will further emphasize when deciding what kind of wall system for the building envelope to use such as:

• Increased emphasis on R-value for decreased heat transfer.
• Continued emphasis on control of moisture.
• Increasing emphasis on control and reduction of air movement.
• An orientation toward a systems approach to solving these issues in combination.
• Emphasis from manufacturers and a demand from customers for cost savings.

“As the industry continues to adopt more modern methods of wall design, multifunctional components or components that have demonstrated compatibility with each other will become more prevalent to respond to builders’ needs for better, more efficient solutions while challenged with a dwindling labor pool and rising labor costs,” he predicts. “With continuous insulation solutions like polyiso rigid insulation, we are now able to achieve higher R-values with fewer layers and materials in a wall, which reduces the overall building footprint while still providing moisture, air and thermal barriers in a single product and reducing labor with the opportunity for single-pass installation of multiple functions.”

Collaborative Future

Christina Saunders, applications engineer, Alucobond Aluminum Composite Material by 3A Composites USA Inc., Davidson, N.C., agrees that with the increasing numbers of buildings clad in metal, it is vital that our industry focus on improving building envelope efficiency. She believes this should be done not only to reduce heating and cooling costs for building owners and residents but to lessen the overall effect of this energy consumption on our environment through sustainable building design.

“We need to pursue the development of high-efficiency building envelopes in a more collaborative manner by sharing our efforts as a group of metal cladding manufacturers and fabricators/installers through organizations such as the Metal Construction Association,” she says. “Additionally, we need to work together to improve the performance of these increasingly complex building systems that often include aluminum composite material installed as exterior cladding over both insulation and weather barriers by collaborating with those product manufacturers as well. In order to improve energy efficiency of envelopes for metal buildings, we need to the look at these challenges as a whole and share our findings with all component manufacturers.”

Todd Sackmann, market manager, Wausau Window and Wall Systems, Wausau, Wis., predicts collaboration with the design team will take on a greater importance as building product manufacturers’ involvement becomes more valued for interfacing with adjacent trades and in contributing to the whole building analysis. “This will continue to take on greater importance and value as coordinating designs to keep up with the advancing codes, to deliver creative designs and to meet customers’ desires, especially when aggressive schedules are part of the equation,” he says.

Tomorrow’s Bigger Challenge

Continue to see all buildings be designed to use less energy and eventually be net zero. But because of steel’s high thermal conductivity, metal buildings will present a bigger challenge when it comes to reducing energy used to heat and cool them. Insulation and metal building manufacturers will continue to develop highly energy efficient wall and roof systems. Again, the move toward net zero buildings will require close coordination between the architect and the construction company regarding the insulation system, the doors and windows and HVAC system.

“Reducing the energy loss through the opaque portion of the building envelope requires a balanced approach including walls, roofs, floors, doors and windows with lower thermal conductivities,” says Charles C. Cottrell, vice president of technical services, North American Insulation Manufacturers Association (NAIMA), Alexandria, Va. “Increasing the energy efficiency of the roofs and walls is best accomplished by increasing the thermal resistance wherever the largest thermal shorts are, typically where girts and purlins intersect with the heavy steel structure and the insulation can be the highly compressed. Insulation systems that increase the thermal resistance at these areas where thermal shorts occur include taller clips that allow thicker insulation and thermal blocks made of materials that prevent compression can significantly increase the building’s thermal performance.”

Cottrell predicts fiberglass and mineral wool will continue to play a large part in meeting the goals for lower and eventually zero energy buildings because of the variety of forms the materials come in, their excellent fire performance and low cost compared to many alternatives.

Codes and Standards

Energy codes and standards are driving the future of metal building envelope energy efficiency. In recent years, a great deal of attention has been given to the thermal performance of the metal building envelope since improved energy efficiency via enhanced insulation systems is a foregone conclusion. Hal Robbins, technical director, Lamtec Corp., Bethel, Pa., says there is currently a metal building working group within the ASHRAE 90.1 Envelope subcommittee, devoted to thermal insulation options for metal buildings. This group has completed work on new flexible fiberglass and continuous insulation options for metal building walls that will appear in the appendix tables of the 90.1-2016 standard. The group is now starting similar work to address roof insulation options.

“Air leakage and its impact on the thermal performance of the building envelope is the next major frontier,” predicts Robbins. “Current energy codes and standards have provisions in place for air barriers and maximum leakage rates for materials, assemblies and whole buildings. Efforts are in place to require more stringent inspection and testing of air barrier assemblies and whole buildings. With this being said, fundamentals and workmanship will become more critical than ever to ensure that the building envelope is a tight as possible and that air leakage is well within allowable limits. Controlling air leakage is critical and will become a major consideration in the future. Whether this is done with a separate air barrier or combination of an air barrier/ vapor barrier, it is something the architect and/or building designers will need to determine.”

To address such future envelope challenges, Sackmann foresees product improvements in both the glazing systems and the components that go into them. “Better performing insulated glass spacers and coatings, larger thermal breaks, higher capacity hinges and rollers, and lower-operating force handles are sought after in U.S. commercial construction applications,” he says. “Non-traditional window and curtainwall accessories also are increasingly part of the design solution, like dynamic glass, exterior shading devices, interior light shelves or integrated mechanical operators.”

Flexible, Efficient, Versatile

As codes, standards, regulations and the path to net zero continue to drive innovation in high-efficiency envelopes, Jason Zeeff, vice president of sales, Dri-Design, Holland, Mich., predicts more systems designed with flexibility, where the buildup of the envelope and the incorporated components can be arranged to meet the specific needs of the environment.

“This need for flexibility will be true for design, as well,” he says. “Architects will not want to restrict their imaginations to produce an efficient building. The greatest amount of flexibility in both these areas can be achieved by separating the pieces of the envelope. This allows options to be chosen the same way you would buy a careverything you want, without any of the add-ons you don’t need. The most efficient systems will also be those that can achieve low-maintenance longevity. There is nothing more inefficient than having to maintain, repair or even replace products that have failed. I am definitely excited to see how the building envelope can keep evolving and improving.”

David Cook, principal architect, structural and architectural evaluation, CTLGroup, Skokie, Ill., agrees and predicts that metal buildings have an extensive future with high-efficiency envelopes, citing their versatility and economics. “Metal cladding can be used as an effective rainscreen system over alternate wall systems such as sheathed steel framing or concrete masonry unit structures,” Cook says. “It can also be used as a fully insulated sandwich panel.

Metal panels seem to be inherently efficient. Their cladding is made from one of the most recyclable construction materials. Since the panels can be somewhat larger and metal is typically impermeable to air or moisture vapor, they limit areas of potential air infiltration, or water leakage to panel joints and fastener penetrations. These locations can be readily addressed in the manufacturing process using specialized interlocking shapes that effectively and efficiently seal against air and water leakage.”

Durable and Functional

Sarah Gray, P.Eng., project principal, building sciences national leader; Nicole Parsons, P.Eng., senior engineer, building sciences; Carly Conner, M.A.Sc., project manager, building sciences; Hannah Thevapalan, M.Eng., project manager, all of WSP Canada Inc., Toronto, know high-efficiency building envelopes. They contend a high-efficiency building envelope’s goal is to be constructible, durable, and functional, and believe this is certainly true for metal structures and metal cladding systems. They too foresee more collaboration, and advocate for and predict an integrated design approach in which the building owner, design team and contractor work together from the start of a project to strategize the use of innovative metal systems.

“As architects and engineers develop metal envelope systems, we need to keep in mind that the design on paper should be executable during construction,” they say. “The key is identifying and drawing out critical design details far ahead of actual construction to ensure that they are simplified, or at least clearly understandable, to manufacturers and installers.

“With any design that hopes to achieve energy efficiency, providing continuous insulation in the building envelope will minimize thermal bridging between the outer cladding and the interior building structure. Using computer modeling, we are learning that applying insulation outboard of the structure as part of the cladding system is typically the most effective strategy. To achieve this intent, cladding connections and flashing details need particular attention to avoid thermal bridges between outside to inside. New and improved clip-and-spacer systems continue to be introduced into metal architecture today. Insulated sandwich panels that come in a range of shapes, colors and textures reduce thermal bridging as well.