There are many types of insulation available: fiberglass, mineral wool, spray foam, rigid board, reflective insulation, etc. But when it comes to specifying the proper insulation for a single-skin metal wall façade in conventional construction, what is the best type for your project? We spoke to industry experts to find out what architects need to know.
Tips from the experts on the types of insulation available for single-skin metal wall façades in conventional construction
Sherwood Middle School in Shrewsbury, Mass., features 3-inch-thick horizontal MetalWrap Series 200 panels from CENTRIA. Photo courtesy of CENTRIA.
Thermal Performance
The use of insulation is an important way to reduce the loss of energy by preventing heat gain or loss through the building envelope. The reducing of unwanted temperature changes decreases the energy demand of heating and cooling systems.
East Coast Metal Systems, Triadelphia, W.Va., is a full-service fabricator and installer of engineered architectural metal and exterior envelope systems, who works along their single-skin and insulation team, which includes their sales representative at Rock Hill, S.C.-based CarolinaREP (Carolina Rainscreen and Envelope Professionals), for Salisbury, N.C.-based Maxlife Industries provider of ArmorWall sheathing, a high-strength and fire-resistant commercial exterior insulated wall sheathing product. John Trifonoff, vice president at ECMS, notes that it is important to maintain the thermal envelope integrity of a metal wall system by minimizing thermal transfer.
Closed-cell spray polyurethane foam is installed as exterior continuous insulation. Photo courtesy of Icynene-Lapolla.
Julie Schessler, product manager–rainscreen systems with Moon Township, Pa.- based CENTRIA, says it is important to select an insulation solution that is engineered to deliver thermal performance that will meet existing building codes. “Continuity of insulation is important. When looking at the make-up of the building envelope, designers, architects and specifiers must also work to ensure that the components form a barrier to keep the insulation free of moisture so it does not lose its effectiveness. The solution must also work to eliminate thermal bridging.”
Thermal bridging is the loss of building energy though the thermal conductivity of elements that bridge across the insulation of a wall enclosure of a conditioned space when the outside temperature is warmer or colder than the interior space. Minimizing thermal bridging is important relative to the performance of insulation. Jay Saldana, PE, senior engineer–commercial with Houston-based Icynene-Lapolla, adds, “Metal skins can also get really hot and it is important to have a proper airspace between the cladding and the insulation to allow heat to have a chance to dissipate. Additionally, it is important that the insulation be capable of handling the heat that could be projected from the metal cladding.”
The way in which a metal panel system attaches to the framing also plays an important role. Different types of metal panels from different manufacturers tend to have different cladding attachment methods. “Understanding the cladding attachment and knowing which is better for limiting thermal bridging and allows for easier install of the continuous insulation will provide the most efficient result from a thermal and time management point of view,” Saldana says.
Photo courtesy of CENTRIA.
Types of Insulation
There are many different types of insulation available, each with their own specific properties and benefits. Here are some of the most popular ones used in single-skin metal wall façades in conventional construction.
Fiberglass/Mineral Wool/Foam Board
According to Mike Smith, technical manager at Silvercote LLC, Greenville, S.C., single- and multilayer faced and unfaced cavity fill glass wool is used most often in conventional construction. “Glass wool is a very cost-effective insulator and a familiar product to most installers,” he says. “There are glass wool assembly options that meet the current energy standard/code requirements for each climate zone.”
Smith says mineral wool, which is composed of primarily basalt (volcanic/igneous rock), is commonly used in fire-rated wall assemblies since it has a higher R-value per inch that glass wool. And, in situations where available space is at a premium, Smith adds rigid board can be useful as it typically has a higher insulating value per inch. “Polyiso board has a high R-value per inch, so it is good needing a consistent, uncompressed or continuous insulation where limited space is available.”
Different insulation types provide varying levels of benefits including thermal value, compressive strength, water/vapor permeance, mold growth, and flammability/smoke development, says Ryan Miller with Max Life Industries. “All of the most common types of cavity insulation, XPS, polyiso and rock wool, are now available in a high enough compressive strength to apply subframing outboard (through), thus assisting in maintaining thermal continuity,” he explains. “However, foam plastics and thermal values weigh heavily in decision making in commercial facilities. Furthermore, it helps maintain standard details across any metal wall panel system, as well as eliminate scope or trade overlap by providing the installer with a monolithic attachment substrate.”
According to Trifonoff, rigid foams tend to carry higher thermal values per inch, such as polyiso (+/-6.2), but may not comply with NFPA 285. Semirigid blankets, such a rock wool, may carry a lesser thermal value (+/-4.2), but does carry other valuable properties. “It is up to the designer of record to design what is best suited for the application,” he says.
Contractors apply closed-cell spray polyurethane foam insulation. Photo courtesy of Icynene-Lapolla.
Spray Foam
There are two types of spray polyurethane foam insulation: closed-cell and open-cell. “Closed-cell spray polyurethane foam insulation generally has a service temperature of 180 degrees, which should accommodate the metal skin cladding,” explains Saldana. “Spray foam insulation can also uniquely form and adhere to all pre-installed cladding attachment components, allowing for the best chance at limiting air and water intrusion around these components, compared to rigid products that would require additional materials and labor at every penetration to seal them.”
Only closed-cell spray polyurethane foam should be used on the exterior side of a building wall. “Closed-cell spray foam can adhere directly to the exterior sheathing and become the wall’s insulation, water-resistive barrier (WRB), air barrier and vapor retarder,” adds Saldana. “The unique ability of spray foam to adhere to most construction materials means if another insulation was used in a particular location of the building, the spray foam could adhere to it to maintain a continuous line of insulation on the wall surface.”
Additionally, Saldana says closed-cell spray foam can save time by not requiring time-consuming cutting of rigid insulation to fit around cladding attachments. “Spray foam adheres to the exterior sheathing and cladding attachment to form a thick, continuous insulation, air barrier and WRB without the need for labor-intensive penetration sealing and board joint sealing.”
Contractors apply closed-cell spray polyurethane foam insulation. Photo courtesy of Icynene-Lapolla.
Reflective Insulation
Reflective insulation systems help to reduce the enormous heat gains that exist in metal wall systems, says Kelly Myers, national sales manager, rFOIL Insulation Products by Covertech Fabricating Inc., Etobicoke, Ontario, Canada. “Direct sunlight can make metal roofing and walls extremely hot, and that heat energy radiates into these buildings,” he explains. “Reflective insulations effectively block up to 96% of this energy by redirecting the radiant waves away from the insulation.”
Myers goes on to note that due to foil’s low-emittance properties, reflective insulation is also effective at keeping heat within a building during the cold seasons. “Foil has an inherent inability to emit, or cast off, heat away from itself, much like a foil survival blanket can help a person stay warm,” he says. “This interruption of outward heat flow helps a building retain heat better during cold weather. And, since this heat is likely retained near the ceiling, circulating fans are helpful at bringing the heat toward the floor and occupants.”
Additional benefits of reflective insulation include condensation control. Myers says reflective insulation with a bubble core provides a thermal break beneath metal panels. “This greatly reduces the likelihood of interior moisture forming on the inside of the insulation.”
Sherwood Middle School, Shrewsbury, Mass. Photo courtesy of CENTRIA.
Energy Codes
Where a project is located will determine which minimum energy codes it is required to follow. Many states and municipalities have adopted different versions of the various energy codes, and it is important to know which are applicable where you are building. As Smith notes, many states have adopted a version of ASHRAE 90.1, Energy Standard for Buildings Except Low-Rise Residential Buildings, or the International Energy Conservation Code (IECC).
When it comes to continuous thermal performance, ASHRAE 90.1 notes that “Insulation that is continuous across all structural members without thermal bridges other than fasteners and service openings. It is installed on the interior, exterior or is integral to any opaque surface of the building envelope.”
“Therefore,” Smith explains, “glass wool installed over the framing from base angle to the eave, though physically continuous, is not continuous per the code as where it crosses the framing is compressed and therefore not thermally efficient.”
Additionally, “Most energy codes are based on R-value testing,” Myers notes. “R-values are ideal for measuring the effectiveness of conventional mass or fiber insulations. However, R-values alone understate the effectiveness of a reflective insulation. R-values are directly related to resisting heat flow by conduction and convection, but do not effectively measure the value of insulation against radiant heat flow.”
For example, Saldana notes closed-cell spray foams have a better R-value per inch than other rigid insulation options. “If designed with spray foam in mind, the exterior wall may be able to be as much as an inch thinner using R-7/inch spray foam versus R-5/inch rigid board.”
To determine the thermal values required by the applicable codes, Schessler notes architects should coordinate with HVAC engineers. “Also, will the single-skin cladding shed all the water to keep the insulation dry? This is a key consideration,” she adds. “What are the humidity requirements for the building being designed? Insulated back-wall panels [see sidebar] have performance characteristics that exceed the high humidity requirements required by facilities such as hospitals.”
One aspect of the building codes projects may have to comply with is the requirement of the wall system to meet NFPA 285, the Standard Fire Test Method for Evaluation of Fire Propagation Characteristics of Exterior Wall Assemblies Containing Combustible Components. Because metal conducts heat, Saldana says NFPA 285 is important to pay attention to. “Every insulation will have different approvals for NFPA 285, so it is critical that these approvals are reviewed before listing a potentially combustible insulation, like foam plastics, into an exterior wall with a metal cladding,” Saldana explains. “Some closed-cell spray foams have NFPA 285 approval with metal claddings and some don’t.”
Since NFPA 285 is an entire assembly test that is product specific, Miller notes that architects, specifiers and contractors need to understand that coordination of the requirements are critical in situations when the scopes of work are separated for construction.
Given the variety of insulation options available, it’s important to know and understand the different performance characteristics of each, and how that matches with the specific requirements of the building. “Architects want to know and trust that a specific system is going to deliver what it promises,” Schessler says.