Stone wool insulation: Improving open-joint cladding systems

by arslan_ahmed | March 23, 2023 10:00 am

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By Brendan Van Gool

The primary function of a wall system is to act as an environment separator. For the last 50 years, the components and design of cavity wall systems have undergone a significant transformation in North America. Higher energy efficiency, more stringent fire safety requirements, sustainability, durability, and better overall performance are driving design changes, and consequently, a shift in requirements to satisfy codes and standards.

At the same time, there is also increasing demand from architects for greater flexibility in design to satisfy aesthetic goals. This affects what happens within the exterior wall construction, as well as on the visible exterior.

Sealed-joint cladding systems are no longer the de facto standard. In such systems, the joints are intentionally sealed to limit the potential for water intrusion. However, since walls will always get wet—whether it is through broken pipes, cracks, or moisture from air leakage—the limited airflow behind the cladding can also contribute to numerous issues, including mold growth and corrosion of materials. By contract, rainscreen systems, such as open-joint and ventilated systems, are increasingly popular in North America. While the gaps may allow water to get behind the cladding, the increased airflow improves the assembly’s drying ability. These systems also have the added benefit of giving architects the design flexibility they seek—varying textures and depth that come with selecting different materials and assemblies.

Insulating in open-joint systems

The building envelope in open-joint systems still needs to serve its primary function, which is control of heat, air, and moisture. One key to a successfully constructed open-joint system is the selection of insulation material, and builders increasingly recognize the many benefits that come from the use of stone wool.

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Todd Kimmel, chair of Rainscreen Association in North America (RAiNA) and board member of New York Passive House, says semi-rigid stone wool insulation boards are an ideal option for continuous insulation (ci) on a building’s exterior.

“Codes are asking for increasing amounts of ci to meet the R-value and U-value requirements of ASHRAE 90.1; and there are new test standards under consideration, for example, to evaluate ventilation and drainage potential of products in rainscreen systems where ci is used.”

According to Kimmel, stone wool insulation boards will deliver on these performance requirements, including thermal comfort, energy efficiency, fire protection, water repellency, and sound insulation, even when exposed to the elements. However, in an open-joint system, it is also important for the material to not detract from the aesthetic of the design.

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New options for open-joint systems give even greater design flexibility

In most open-joint systems, the small gaps in the cladding will not be visible from a distance. However, where gaps are more pronounced, or when the architect wants to ensure a clean and consistent look, stone wool insulation boards are now available with an integral facing of bonded black matte fleece, leaving the appearance of crisp, black lines. The fleece is a glass fiber tissue with a black organic mineral coating and is chemically bonded to the insulation during the manufacturing process, offering better mechanical properties and superior long-term performance. It can withstand long-term ultraviolet (UV) exposure with no significant loss of depth in color.

Previously, to achieve the same look, the only option was to include an additional layer to the assembly. Many cladding component manufacturers have added this type of separate facer to their portfolios, but installation and materials for the additional layer tend to be more costly and labor intensive than the use of a single product with an integral facing.

ASU’s Interdisciplinary Science and Technology Building 7

Specialty commercial contractor MKB Construction in Tempe, Arizona, brought this new fleece-faced insulation board solution to the attention of the general contractors building the new Interdisciplinary Science and Technology Building 7 at Arizona State University (ASU). Project manager Cameron Geske recognized the opportunity it would provide to the building’s designers; they were challenged with a facade that reflects innovation, which is central to the new research center in its visual design, without sacrificing the performance required from various assemblies to support the sustainability goals.

The facade is a unique geometric system of overlapping glass fiber reinforced concrete (GFRC) panels with open joints, installed over the backup wall behind it. It would be necessary to design this open-joint assembly in such a way as to ensure the performance of the building’s envelope, while being exposed to the elements—all while maintaining its aesthetic appeal.

The matte black fleece-faced rigid stone wool insulation board was eventually specified after other approaches, including an insulated metal panel system, failed to meet the unique challenges presented by this design for an open-joint facade.

“This solution fit the bill for so many reasons,” says Geske. “We had worked with stone wool insulation on past projects and knew it would meet our needs for consistent R-value and superior thermal performance, as well as its fire-resistant and sound insulation properties.”

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The rigid stone wool boards used as exterior ci are also frequently recommended by contractors such as Geske because they are relatively easy to install. The matte black fleece-faced option went even further, as Geske’s team was able to install it under the open-joint cladding, knowing it would not be damaged by exposure to rain and UV light. Building on the features and benefits of the original insulation boards, the matte black fleece-faced option also offered the project’s architects and builders the clean visual aesthetic they wanted in the open-joint system.

“No one wants to see the insulation through the seams in the facade,” adds Geske. “The thin black facer on the insulation boards meant we did not need to apply another layer to cover up the board; it was an efficient and effective solution.”

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Multi-unit residential retrofit in NYC’s Upper East Side

The crumbling facade of 201 East 79^th Street was the starting point for a retrofit, which would include an innovative porcelain tile cladding system as well as a high-performance and long-lasting rainscreen support system. This 160-unit residential co-op, constructed in 1961 in New York City’s Upper East Side, was an example of the white glazed brick buildings that characterized the area’s development projects of that particular era. The original building design prioritized comfortable units with large, spacious rooms in keeping with the upscale neighborhood. However, the economy of means also dictated a purely functional design of the facade. As the building aged, facade safety inspections required by NYC’s building code uncovered structural and masonry failures—requiring repairs at significant costs and inconvenience to the building’s residents. Facade probes showed the exterior walls had no insulation at all, and in addition to the failing glazed face-brick, the backup masonry had been poorly installed. In short, the facade was failing. By 2018, it became clear; a full facade recladding was in order. Rogers Partners Architects + Urban Designers were brought in to design the new cladding for the building; they also used the opportunity to recommend a complete retrofit of the building envelope with a high-performing rainscreen system, which would improve thermal performance, acoustics, comfort, and safety for occupants—all while accommodating the aesthetic goals of the owners.

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The architects faced multiple challenges, on both the technical and design fronts. First, Rogers Partners knew the removal of the brick offered a chance to repair the holes in the deteriorating concrete block backup, which provided little to no protection from the elements or busy city streets. It was not uncommon for residents to feel drafts through electrical outlets and around windows, and exterior noise was also a regular complaint. Second, the retrofit was funded by the building’s owners; it was a substantial investment, so compromises were made to stay within the budget. One of those compromises was not replacing the windows immediately; this decision was left up to the individual owners. Therefore, the new window trim had to be constructed in a way to accommodate window replacements at a later time. The building being occupied also came with challenges, since all demolition and new construction had to be achieved from the outside, to minimize disturbance to the unit owners. Additionally, and more critically, ownership had raised real concerns about flammability issues associated with early-generation rainscreen systems that left occupants vulnerable in the event of fire.

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The architects were convinced a rainscreen system was the solution to address all the challenges presented. They proposed a cost-effective porcelain tile cladding material fastened with exposed clips. Zoning regulations permitted a 101.6-mm (4-in.) encroachment over the property line; this enabled them to expand the width of the exterior wall with the retrofit to allow room for a high-performance assembly, designed to meet Passive House standards for the solid wall portion of the facade. When it came to materials for the new building envelope, stone wool insulation was the first choice, primarily because of its superior fire-resilient properties, as well as its ability to deliver thermal performance and comfort.

Rigid stone wool insulation boards—both unfaced and with the matte black fleece layer—were specified for the project. The building’s new facade used an open-joint system, requiring the assembly materials to meet needs for aesthetics, durability, and energy efficiency. Where the insulating material is visible in these open-joint systems, the stone wool insulation boards with the matte black layer do not detract from the design. Further, both stone wool products provide exceptional moisture resistance and drying properties, making them an ideal component for rainscreen systems.

The metal framing for the new cladding was bolted into the original concrete block backing (now repaired and sealed with a liquid-applied membrane) and the stone wool boards were quickly and efficiently installed behind the framing. Around the windows, the architects designed a custom beveled-edge system to accommodate the new envelope assembly for airtightness and still allow for the window units to be replaced and resealed at a later time.

Stone wool is easy to cut, enabling crews to trim the material to fit with the inconsistent detailing and spacing around original and newer window installations. The last stage of the assembly was attaching the porcelain tiles with an innovative clip system; the non-combustible tiles were an important component of the fire-resilient design of the entire assembly.

“We chose to specify rigid stone wool insulation boards for this project because it met so many of our needs, and there were a lot of them,” says Alissa Bucher of Rogers Partners Architects + Urban Design. “The rainscreen assembly needed an insulation material that would deliver on thermal performance, fire protection, acoustics, and of course, durability. It also needed to work with the design of the unique porcelain tile we chose for the facade. Stone wool was the go-to material. Four inches [101.6 mm] of stone wool in these walls will help ensure the new exterior will stand the test of time.”

Complete solution for open-joint systems

The move towards open-joint rainscreens means the joints between the cladding elements are intentionally left open, principally to provide superior drying potential, and with the added benefit of greater flexibility in designing the structure’s exterior aesthetics. Innovations such as black fleece-faced insulation boards show there is no need to compromise the system’s performance in order to achieve good aesthetics. An open-joint cladding provides optimum protection against the impact of water when the system is designed with proper drainage and ventilation. Additionally, since stone wool insulation products are hydrophobic in nature, they repel water and resist rot and mold. If water does enter the insulation from snow or wind-driven rain, it can dry out due to the higher drying potential of stone wool—making it an ideal choice for
open-joint rainscreens.

Author

Brendan Van Gool is the product marketing manager for building insulation at Rockwool, a global stone wool manufacturer with five facilities in North America. Van Gool has been with the company for more than six years, providing knowledge and experience in areas of product management, technical services, customer relations, and marketing and business development.

Source URL: https://www.constructionspecifier.com/stone-wool-insulation-improving-open-joint-cladding-systems/

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