Therm All May19 1 Lowrez

Interior of Pacific Insulation Products' R-Seal, a rigid board continuous insulation product. (Photo courtesy of Therm-All Inc.)

Continuous insulation (CI) with its rigid foam material properties, can cover entire surfaces and be fixed to either the inside or outside of exterior walls. In addition to boosting R-values (thermal performance), which prevents heat from escaping, CI also reduces moisture damage in the building envelope by lowering condensation within the envelope assembly resulting from vapor diffusion.

CI is now mandatory in most buildings to meet the requirements of the 2015 International Energy Conservation Code (IECC) and ASHRAE 90.1. The Energy Standard for Buildings Except Low-Rise Residential Buildings states that, "a continuous insulation installed over the studs, such as ridgid foam, must also be applied." Here are some installation tips and techniques on installing CI correctly for light-gauge steel framing.

Before Starting CI Installation

Francis "JR" Babineau, research manager/building scientist at Johns Manville in Littleton, Colo., says the fundamental procedures for installing rigid CI over a steel-framed wall start with a few questions:

1. Will the CI also be used as the air barrier and/or drainage plane for the wall?

2. What is the thermal performance requirement for the wall?

3. What is the cladding and how will it be attached?

Babineau explains the answers to these questions will drive how thick the CI needs to be, whether joints, seams and penetrations need to be sealed, and what other components may be needed. "Once we get to the actual installation steps, fundamental items are related to fitting the CI pieces snuggly together, and properly integrating around windows and the cladding attachment system," he says. "If the CI will also be the air barrier and drainage plane, it is critical to seal all penetrations and joints, and integrate with all windows, doors and penetration flashings."

Before starting CI installation, install a proper air and moisture control barrier with a vapor open profile that is sealed, finished and tested. A proper CI barrier should be a supplemental moisture control protection layer for the primary air barrier.

"Flat board stock insulation that is in direct contact with the air barrier will reduce the wall's ability to dry," says Dean Seibert, vice president of sales at InSoFast, Mitchell, S.D. "The industry has developed several methods to provide a capillary break between the insulation and the air barrier as to not negate the air barrier's vapor open performance. Drainage mats being one such solution."

Johns Manville AP Foil-Faced Polyiso Foam Sheathing was used in this renovation project on the steel-framed exterior wall as a weather resistive and air barrier to prevent water and air leakage behind a brick cladding of a local school. AP Foil, combined with flashing tape, is an effective solution for preventing air and water leaks in walls, as well as preventing thermal bridging in steel-framed walls. (Photo courtesy of Johns Manville)

InSoFast continuous insulation bridges across the structural framing members reducing thermal bridging even at the recessed screw attachment points. The cladding's attachment is then thermally isolated from the building's light-gauge structure. (Photo courtesy of InSoFast)

Installation Details

After these preliminary steps, most CI installation details start to vary. Seibert believes most involve mechanically attaching the insulation panels with screws and washers directly back to the light-gauge steel framing, then taping and sealing all the insulation board joints as an added air and water barrier protection layer. "The next step in application is to attach some form of furring or attachment rails and standoffs that are mechanically attached back to the light-gauge steel framing. These rails or furring are installed to provide a means for affixing the cladding or finishing material of choice."

"There are several [installation] procedures that depend upon whether or not the rigid insulation is a standalone or composite material," says Tom Oliver, district manager at Therm-All Inc., North Olmsted, Ohio. "If it is standalone, a sheathing would be required as an additional component. If it is a composite material like a SIPS panel, the sheathing and rigid board is one unit."

Seibert contends fibrous insulation with its metal channels in direct thermal contact with the interior structural framing is a "lawsuit waiting to happen." "Humidity runs through insulation like this like water through a screen door on a submarine," he adds. "Water condenses at the critical hotspots or cold spots at the intersection of what will soon be a rusted-out structural attachment. At that screw point [the structural connection], the dissimilar metals come in contact and, at a critical point, water will condense and create a galvanic action. Rusting out at a structural connection is bad."

Continuous insulation covers entire surfaces, providing R-value where cavity insulation cannot. (Photo courtesy of Cold-Formed Steel Engineers Institute)

The main impact of energy code compliance has been increased CI thickness. This has led to greater challenges integrating with windows and doors, which sometimes have to be bumped out with additional framing to support the window flush with the exterior of the CI. "Conversely, if windows are left back within the steel framing, an 'innie' window is created, which requires additional flashing and drainage to prevent window leaks," says Babineau. "To avoid these challenges, CI thickness is often minimized by utilizing trade-offs through energy modeling, which can allow reduced CI thickness for improved energy performance in other areas of the building."

Thermal Bridging

The effects of thermal bridging are especially critical when it comes to light-gauge steel framing—heat can pass through the path of least resistance: the steel stud. But Babineau contends just using CI over steel stud walls addresses many of the thermal bridging issues created by steel framing. However, he cautions another key issue is how claddings are attached. "More traditional cladding attachment systems, such as vertical z-girts, can end up creating a whole new set of thermal bridges through the CI," he says. "Cladding attachments that run perpendicular to the framing can help reduce this effect. Even better are the many nonmetallic cladding attachment systems that reduce these secondary thermal bridges even more."

Bill Lippy, president and CEO of Fi-Foil Co. Inc., Auburndale, Fla., explains that, "Steel basically has an R value of zero; you want to cover it up completely. Make sure there's a good coverage there, and again, it's just continuous, it's down to the detail. They're not missing much, because any kind of void or compression is going to certainly be noticeable in the building envelope's overall U value, especially if they inspect it afterwards with a thermal camera. These issues could lead to issues beyond thermal performance."

Johns Manville AP Foil-Faced Polyiso Foam Sheathing boards serve as a continuous insulation solution, protecting against thermal bridging and the transfer of moisture and air for this project in Atlanta. (Photo courtesy of Johns Manville)

Lippy says that when CI is installed on outside walls, "This exposes the internal cavity on the inside of light-gauge framing, and that framing is probably anywhere from 3 inches to 8 inches deep." He recommends supplementing that on the inside with a mass insulation or a combination of insulation, like a reflective insulation. "For example, a real good solution there would be to air seal that cavity with some spray foam, and that could be open or closed-cell spray foam. That might be a really good overall wall system to address all of the issues that light-gauge steel framing creates in the building envelope.

You're taking care of thermal bridging, you're taking care of air sealing, you're taking care of the moisture intrusion, and you're taking care of the overall thermal performance. You've done it probably with the most cost-effective combination as opposed to just loading it up with continuous insulation on the outside or a lot of spray foam on the inside."

Seibert claims dealing with CI thermal bridging is relatively easy and contends the CI installation problem is with moisture. "Light-gauge-steel framing has zero moisture capacity. Water vapor, AKA relative humidity, is being driven out from the interior during the cold weather months by a vapor drive. Then as the seasons change, moisture movement is inward by wind-driven rain from the exterior condition. Moisture movement and control becomes a critical design element in light-gauge steel framing. An important, unintended consequence of exterior insulation is we slow down the energy loss through the walls and reduce the walls ability to dry."

Stressing the Basics

Lippy contends that since quality CI is really about its installation, adhering to basics is really important. "You can take any insulation product and make it work for the building. You can also have the best insulation product and make it terrible for the building. And it really comes down to the details of the installation. From that standpoint, it's always good to have—if you're a building owner, architect or builder—an energy rater as part of your team. Because they're going to provide you quality assurance that is going to underscore and probably assure that grade one install."

(Photo courtesy of Therm-All Inc.)