By Jay Fox

Exterior insulation and finish systems (EIFS) have become more common within the last ten years as more owners have become interested in energy efficiency and optimizing the performance of their buildings. At their most basic, EIFS can be thought of as enhanced cladding systems that shed water, allow drainage, and improve thermal performance by integrating a layer of continuous insulation into the exterior wall system, thereby minimizing thermal bridging.

In North America, the insulation contained within EIFS has typically been expanded polystyrene (EPS) or extruded polystyrene (XPS). These options are also available in Europe, but European EIFS have also used high-density stone wool. More recently, ROCKWOOL has begun working with EIFS manufacturers in North America to incorporate their stone wool products into EIFS that are available in the U.S. and Canada. As explained during a recent Component Spotlight featuring ROCKWOOL, this is a boon to builders in North America, especially if they are operating in states or provinces where building and energy codes are more stringent and fire resilient wall assemblies are in higher demand.

Stone wool’s fire resilience is well known. It can maintain performance levels even at temperatures of up to 1200°F (650°C) and is capable of withstanding temperatures exceeding 1000⁰ C (1832⁰ F), so it naturally lends itself for use as a fire blocking material within exterior wall systems. This makes it an ideal building material in areas that are adjacent to undeveloped spaces (e.g., the wildland-urban interface [WUI]) and densely populated cities where buildings are separated by limited or even no lot lines. Beyond that, there are several advantages to using stone wool over other types of insulation. Stone wool:

• Is vapor permeable and dries easily

• Maintains consistent thermal performance

• Has exceptional acoustic performance

• Does not expand, warp, or contract

• Is UV stable

• Cannot serve as a food source for mold, mildew, or pests like termites

As stone wool does not need additional flame retardants or other chemical agents to achieve these benefits, ROCKWOOL products are listed in the Living Building Challenge (LBC) as Red List Approved. ROCKWOOL products also contain significantly less embodied carbon than many types of foam insulation. They are also lower in embodied carbon than comparable mineral wool products manufactured by competitors. For more information about ROCKWOOL’s commitment to health and sustainability, please refer to their transparency page for links to environmental product declarations, health product declarations, and other declarations from third-party verifiers.

As ROCKWOOL US Senior Manager of Sustainable Solutions Todd Kimmel explains in the above Component Spotlight, ROCKWOOL does not only promote sustainable building practices through its commitment to reducing embodied carbon and improving building efficiency. Durability is another factor when it comes to sustainability. Stone wool’s fire resilience, structural stability, and capacity to maintain thermal performance means it can be repurposed even after the wall system it is a part of has been disassembled.

EIFS can be used in new construction or retrofits. However, this post will focus on two Passive House retrofits covered in the recent Component Spotlight: The Ken Soble Tower in Ontario and Engine 16 in New York. Both projects have been certified by the Passive House Institute through the EnerPHit retrofit program. They also exemplify how ROCKWOOL products can complement and enhance EIFS, as well as how ROCKWOOL can be used to make construction easier, resolve unique design problems, and help with increasingly stringent local regulations.

Case Study 1: The Ken Soble Tower

The Ken Soble Tower was originally built in the 1960s, providing nearly 150 affordable housing units to seniors in Hamilton, a Canadian city in the southwest corner of Lake Ontario. Despite being one of the most prominent landmarks in the city, the 18-story tower had become an eyesore because the brick masonry veneer was clearly deteriorating. Conditions inside the building were also getting worse because of a lack of thermal control. Systems were at the end of their life, the lack of insulation combined with poor moisture control had led to mold problems, and even the short-term viability of the building had come into question.

The building’s owners, CityHousing Hamilton, considered tearing down the 80,000-ft² (7,500 m²) tower, but the team at ERA Architects was convinced that it could be salvaged. ERA proposed a Passive House retrofit that would allow the building to remain affordable while cutting emissions by over 90%. They claimed that these savings were possible through improvements to the building enclosure, which would allow the aging HVAC system to be replaced by a far smaller and more efficient electric system (except for the domestic hot water). Passive House certification would also enhance the building’s resiliency to fire, durability, and indoor air quality, providing a comfortable and healthy environment for the seniors who would ultimately call the tower home.

The city approved, resulting in one of the largest EnerPHit projects ever attempted. It received its final certification in 2021.

First and foremost, enhancing the building enclosure involved replacing the existing windows and doors with high-performance fenestration systems. They also recognized that the existing balconies created far too many thermal bridges, so these were eliminated and replaced by Juliet balconies with door-size casement windows that open inward. In addition to eliminating sources of thermal bridging, truncating the balconies also made refurbishing of the façade a lot easier.

To improve thermal performance the team included four inches of ROCKWOOL stone wool insulation (R-17) on the interior of the existing wall system, while the exterior cladding system has made use of a six-inch rigid stone wool EIFS board with an integrated geometrically defined drainage cavity (GDDC) along the back (R-24). Once it is positioned, the stone wool board was then mechanically fixed in place. It was then covered with a reinforcing mesh layer, and then a proprietary EIFS façade developed by DuRock. The effective R-value for the wall assembly is R-38. Beyond thermal performance, the team prioritized creating a fully non-combustible solution because the design of the building occurred not long after the Grenfell Tower tragedy in London. They were adamant about using stone wool insulation in the cladding system because of its fire resiliency.

This phenomenon is similar during outages within periods of excessive heat. ERA did a study of summer outages and found that it takes conventional buildings about half a day to become dangerously hot, whereas Passive House buildings remain comfortable for up to four days. Given that seniors are more vulnerable to health problems due to prolonged temperature extremes, ERA’s study presents a very strong argument in favor of building any senior residence to Passive House standards.

Case Study 2: Engine 16

Built in the 1880s, Engine 16 was originally a fire station on the East Side of Manhattan. After being decommissioned in the 1960s, the building was converted into a church. By the 2010s, the church was struggling to maintain the aging building. Many of the architectural embellishments and materials that had given the original fire station its charm and unique aesthetic had become worn or had been covered up during remodeling.

When the building was sold to new owners in 2018, they immediately recognized that they had purchased a diamond in the rough. They engaged Baxt Ingui Architects (now Ingui Architects) to restore the historical features on the interior; preserve the building’s façade; strength its fire resilience; and dramatically improve the building envelope through enhanced air sealing, a more robust insulation layer, and the minimization of thermal breaks. In addition, they wanted to convert the building into a mixed-use, multifamily building with two additional stories on top of the existing structure.

It should be noted that compliance with Local Law 97 was not a consideration when discussing performance improvements, as the addition brought the total square footage to around 13,000 ft², and the ordinance only places emission limits on buildings over 25,000 square feet. Instead, the owners were motivated by the idea of creating a comfortable space and lowering utility bills through improved systems efficiency.

Compliance with Local Law 126 did help influence the materials used in the exterior wall assembly on the rear façade. Implemented in November 2022, Local Law 126 puts significant restrictions on the use of foam plastics while placing more stringent fire blocking requirements on EIFS. The law mandates fire-blocking with non-combustible materials in concealed spaces within exterior wall coverings. As the rear façade was in a state of disrepair and needed a new exterior finish, using EIFS with ROCKWOOL stone wool offered an almost turn-key solution to the issue while also providing additional R-values and ensuring compliance with Local Law 126. However, EIFS were not applicable on the other walls because it shares a party wall with each of the adjacent properties and the owners wanted to preserve the front façade.

Preservation was a major concern for the owner and balancing the need to protect the historic elements of the building while bulking up the envelope was a challenge for several reasons. Chief among them was the issue of moisture management. Adding more insulation and barriers to any wall assembly can impact the movement of moisture. For older buildings that were designed to allow moisture to freely diffuse through the walls, these new barriers and disruptions in the flow of moisture can compromise the integrity of the brick.

A careful analysis showed that ROCKWOOL’s Frontrock stone wool insulation on the interior side of the masonry would allow better vapor permeability when compared with other insulating materials, meaning that any moisture intrusion would be allowed dry on the inside or the outside of the assembly, thereby helping to preserve the brick. This strategy allowed the owners to preserve and restore the front façade of the building.

Lessons Learned

As these two case studies show, EIFS that incorporate ROCKWOOL products can resolve major design and compliance challenges during retrofits. They can also be used in new construction to help design teams overcome similar challenges, whether they are building in WUI areas, major cities, or anywhere where there’s a demand for comfortable, durable, and fire-resilient homes.