Whether through education, training or in-field failures, building professionals are aware of the need and benefits of a properly insulated exterior in commercial wall assemblies. A well-insulated building envelope enhances energy efficiency by reducing energy loss via convection (air infiltration and exfiltration) and conduction (thermal bridges). The benefits of a well-insulated envelope extend beyond energy efficiency to other performance metrics, such as moisture penetration. The multitude of ways the building envelope can affect long-term performance explains why the subject is often a key component of building code compliance, as well as discussions around high-performance building practices across many parts of the country.

Building and design teams use different practices when it comes to insulating exterior walls. Cavity insulation, for example, can be integrated between structural members, such as wood or steel studs. Using cavity insulation alone fails to mitigate the significant thermal bridging impacts of the structural members, which facilitate heat transfer between indoor and outdoor spaces. This influences the performance of the insulation and the energy efficiency of a building.

To mitigate energy loss due to thermal bridges, building teams are employing high-performance materials, like polyisocyanurate insulation with foil or coated-glass facers, as a continuous insulation solution for exterior walls. This practice insulates the entire opaque exterior of framed walls to reduce energy losses and gains due to thermal bridging. Because polyiso CI has one of the highest R-values per inch when compared to other insulating products, it delivers excellent thermal performance without the need for bulky attachment systems required by other insulation materials. Polyiso CI used in an exterior wall assembly offers additional benefits, like reducing air and moisture infiltration.

Figure 1: A typical wood-frame wall constructed with OSB sheathing and polyiso CI.

Figure 2: A demonstration of moisture transfer through air leakage in a cold-climate wall assembly.

Restricting Air Intrusion with Polyiso CI as an Air Barrier

According to the United States Department of Energy, up to 40 percent of the energy used to heat and cool a building can be lost by uncontrolled air leakage in colder climates through the building enclosure. Any amount of air infiltration can lead to increased energy consumption, especially in older structures located in temperate states that may not have robust HVAC systems in place. To enable stable interior temperatures, minimizing air leakage is crucial.

Polyiso CI can be used as an air barrier system in the exterior wall to mitigate air intrusion. Model building codes recognize polyiso CI as an air barrier material when installed at a minimum 1/2-inch thickness with approved flashing tapes or sealants, per the manufacturer’s installation instructions. In addition to enhancing thermal performance, restricting air movement through the wall with polyiso CI (or other properly installed air barrier materials) can improve occupant comfort and reduce the infiltration of outdoor pollutants and allergens.

When installing polyiso CI in a wall assembly, contractors should seal penetrations for plumbing, electrical, air conditioning, dryer vents and other openings with an approved sealant to ensure long-term performance. Attention should be paid to sealing the inside and outside corners, as well as tying in the air barrier at the roof-to-wall and wall-to-foundation transitions.

Figure 3: A comparison of moisture transfer through a wall due to diffusion versus air leakage.

Managing Moisture with Polyiso CI as a Water-Resistive Barrier

Untreated penetrations provide a path for water ingress and can lead to moisture accumulation in the wall assembly. This, in the end, increases energy transfer and may compromise building envelope performance. Without adequate provisions to reduce moisture entry and accommodate drainage, moisture can lead to potential growth of mold and mildew over time, which can be hazardous for occupant health. If the problem persists, it can compromise the structural integrity of the wall system.

Exterior walls with traditional cavity insulation may need additional air and moisture infiltration barriers, sheathing materials and other components within the wall assembly to ensure optimal performance. This can thicken walls’ profiles and reduce usable floor space.

Mitigating these concerns, polyiso’s closed-cell core inherently resists moisture absorption. In addition, many polyiso CI products with taped or sealed joints can be classified as water-resistive barriers. In application, the insulating layer also provides drainage planes and a secondary line of defense against rainwater intrusion behind cladding. As a result, contractors can use polyiso CI in exterior walls to provide a continuous thermal insulation plane and reduce the risk of moisture condensation in or out of the wall assembly.

It is important to note that sealing along the top and bottom plates of the wall, around all openings, and integrating window and door flashings is critical when polyiso CI is installed as a WRB material.

Polyiso CI Helps Achieve Leaner Walls

Through its multifunctional properties, polyiso CI can be an effective solution to address thermal, air and moisture concerns in exterior walls. A single solution to multiple challenges, professionals can use polyiso CI to achieve desired performance without losing space. This versatility in application translates to leaner walls and more usable floor area, which can be especially useful in retrofit projects.

Polyiso CI is a Three-in-One Solution for Building Performance

A high-performance, multifunctional solution, polyiso CI reduces potential air and moisture infiltration, optimizes energy efficiency and supports more compact wall designs. This versatility makes polyiso CI an ideal choice for wall assemblies in both new construction and retrofit projects, allowing design and building teams to achieve code compliance and enhance occupant comfort without sacrificing valuable interior space.

As state and local codes continue to place greater emphasis on building performance and energy efficiency, building teams can rely on polyiso CI to meet—and often exceed—these evolving standards.