The building envelope is the physical barrier between the conditioned interior spaces of a building and the external environment. Made up of the walls, roof, doors, windows, insulation, air/vapor/moisture barriers and exterior cladding systems, the building envelope is key to an energy-efficient building due to its ability to prevent the transfer of heat into or out of a building.
All the pieces must work together for high-performance buildings
According to Better Buildings, an initiative of the U.S. Department of Energy (DOE), envelope technology accounts for approximately 30% of the primary energy consumed in residential and commercial buildings by determining levels of comfort, natural lighting, ventilation and how much energy is required to heat and cool the building.
To create an energy-efficient building envelope, all these components work to protect the interior structure of the building against the elements. “They all must work in concert, supporting each other, to create a seamless barrier between the interior of the building and the outside environment,” explains Ed Calvert, LEED AP BD+C, WELL AP, LFA, GRP, Senior Engineer, Kalkreuth Roofing and Sheet Metal Inc., Wheeling, W.Va. “This makes a truly energy-efficient structure.”
James C. Tuschall Sr., president of Tuschall Engineering Co. Inc., Burr Ridge, Ill., says the balance comes into play with the coordination and detailing the interfacing of different materials to minimize air and water infiltration.
Michael Smalley, director of preconstruction at St. Louis-based IWR North America, agrees, saying that the key to an effective, energy-efficient building and façade is collaboration during the design phase. “It’s really important that there’s an understanding of all the different parts of the building and how they work together.”
For example, Smalley says it’s imperative to understand how the mechanical systems are going to be impacted by the different levels of opaque wall, versus the fenestration. This extends to understanding where the movement joints are designed to be, and how can you create energy-efficient movement joints, whether it be a reflection joint or an expansion joint. “A façade typically doesn’t leak in the middle of a window or wall,” he says, “it’s going to leak at a transition. At these transitions, if not designed and installed properly, you’re going to get air, you’re going to get water, you’re going to get moisture, and the mechanical systems of the building were not designed to accommodate the added demand that these leaks can create.”
Maxime Duzyk, director of building science and engineering for The Woodlands, Texas-based Huntsman Building Solutions, expands on this idea, saying that all of the components must be properly designed to effectively control water, air, vapor and thermal performance. “If any component is neglected, it can negatively affect the performance of the entire building, regardless of the efficacy of the remaining components,” he says. “Windows and doors must be properly sealed. Walls and roof coverings shall protect the building from water penetration. Air and vapor barriers should be used to effectively control air intrusion and vapor diffusion between the indoor (conditioned) and the outdoor (unconditioned) spaces.”
“Proper insulation thickness and application must be used,” he adds. “Insulation shall be used in all exterior-facing surfaces including walls, roofs and even below grade. The insulation should address thermal bridging. Therefore, U-value or effective R-value requirements should be met as they include thermal bridging in their calculations. Finally, a product that does not settle, is seamless and can resist mold and water, such as closed-cell spray polyurethane foam, can dramatically enhance energy efficiency and durability.”
As John Koury, AIA, NCARB, architect, A M King, Charlotte, N.C., says, energy loss occurs largely at the building openings: personnel and utility doors, windows and thermal transmittance through materials. “It’s important to first understand passive thermal loading of the building, layout and operations. Provide building plans such that the conditioned air does not simply escape at regularly used building openings: front entrances with air locks, truck docks using vertical levelers, drive-in shelter types. Then, link that design with utilization of highly insulative materials. However, even high-performance materials are not effective if the assembly allows opportunities for gaps. Also be aware of passive solar orientation and high-performance glazing.”
New Products and Technologies
New products and technologies are constantly being introduced in the building products market, making it important to stay abreast of all new developments. “It is critical to seek out continuing education and participate in networking events to keep your company viable and prosperous,” says Calvert.
Smalley emphasizes the need to properly vet products before specifying them on a building. “Know how to vet these products. I don’t care if you’re the installer, contractor, owner or architect,” he says. “Learn how to vet these different products and technologies, don’t just go with the next great thing that comes in the door. Check on the performance of it, check it for compatibility with other materials that you know are going to be on that building, in that façade. Check on longevity. Everybody’s got to have a warranty these days, so what is the longevity of this product? What are the differences of it? What are the performances of it? Talk to other people who have used it, even if it’s one of your competitors.”
When it comes to creating a highly energy-efficient façade, the biggest challenge, Duzyk says, is the elimination of thermal bridging. “Metal is a highly conductive material, which can easily transfer hot or cold temperatures directly into the conditioned space,” he explains. “Metal clips/fasteners attached directly to steel studs can create a “highway” for unconditioned temperatures to transfer into the building. The best way to avoid thermal bridging is by using exterior continuous insulation. Using continuous insulation will solve a majority of thermal bridging but cannot eliminate it completely. The metal fasteners used to attach metal panels to the building’s structure will always act as a thermal bridge, but the effects are drastically reduced with external insulation.”
With the exception of insulated metal panels (IMPs), Tuschall notes an energy-efficient wall is usually a rainscreen that relies on the air barrier and insulation behind the metal wall panels. “Using the correct products and proper detailing is key,” he says.
Another challenge is coordinating one contractor’s specific work with that of other contractors. “We must have a willingness to adapt and work as a team on every project,” Calvert says, “without compromising our own rigorous standards.”
Calvert goes on to say that since incoming and outgoing heat and moisture flow in exterior wall systems are an incredibly important factor in building design and construction, he expects to see a large increase in the participation of building envelope and energy-efficiency consultants on projects. “Contractors are going to need to be able to work with and shift across scopes of work and work as a team with general contractors and construction managers to be successful,” he says. “There can be several different contractors working on different scopes of the same exterior wall system on a single project. But all of these different pieces must work together in the end to make an energy-efficient exterior wall system.”
Benefits of Metal Walls
Metal wall panels provide several environmentally friendly features to a project, including being durable and low maintenance. With the variety of styles and finishes available, metal panels can be specified to meet the requirements of just about any project. “Metal wall panel systems are usually not damaged by intense rain, snow, heat or cold, or any other environmental elements,” adds Calvert. “They are incredibly resistant to mold or fungal growth, which can often cause health problems to building occupants. They are also non-combustible and can prevent the spread of building fires.”
While all of these benefits make metal wall panels a good solution for energy-efficient building envelopes, Calvert notes that the one of the biggest advantages is the control of heat and cold, moisture and air across the building exterior boundary, i.e., energy movement. “Insulated metal wall panels or the installation of continuous insulation behind an exterior metal wall panel creates a continuous thermal barrier, which is a key component in energy-efficient structures,” he explains. “Whole building energy modeling, which is quite common in the building design industry today, can easily show that a continuous thermal barrier increases the ability of the exterior wall system to prevent heat and moisture transfer, and reduces the energy load on almost every type of structure.”
Multicomponent wall assemblies—made up of the framing, sheathing, air barrier, rainscreen and metal cladding—can present opportunities at each of the joints for air leakage or future movement. “The individual components may be energy efficient, but a chance for leakage at the component joints will compromise energy efficiency,” explains Koury. “Insulated metal panel systems, made with a foamed-in-place core, metal skins and interlocking panel joints, simplifies the construction detailing, which greatly reduces the number of wall components and minimizes leakage at joints and aged connections. The integrated window systems some of the insulated panel manufacturers offer extend this benefit to the window opening integration.”
While metal wall panels compare favorably against other cladding materials, Koury notes that it’s important that the panels can be fully integrated with the rest of the building skin. “The more that materials become more integrated with each other, the stronger the building envelope,” he says.