Raising the Bar
LEED v5’s New Emphasis on Decarbonization Through the Building Envelope
by Justin Koscher, President of the Polyisocyanurate Insulation Manufacturers Association
Since its launch in 1998, the United States Green Building Council’s (USGBC) Leadership in Energy and Environmental Design or LEED® program has influenced how buildings are designed, constructed, and operated, creating more than 197,000 certified projects across 186 countries, encompassing 29 billion square feet of LEED-certified space, and saving 120 million metric tons of carbon emissions.
In the Western United States, where sustainability is often embedded in policy and practice, states like California, Washington, Colorado, and Nevada lead the nation in LEED-certified projects per capita. These regions will play a critical role in implementing the sweeping updates found in the green building certification’s latest update, the LEED v5, which is USGBC’s most transformative version to date.
Officially launched in April 2025, LEED v5 reflects a decisive shift toward performance-based, carbon-conscious design. The framework’s latest evolution places heavier emphasis on three key areas of impact: decarbonization, quality of life, and ecological conservation and restoration. A foundational theme throughout the new rating system is carbon accountability throughout a structure’s life cycle.
For the first time, reporting and reducing both direct and indirect carbon emissions is a prerequisite in the energy category, with a 25-year projection required for both. This includes operational carbon projection and embodied carbon quantification. Such a position puts opportunity with Western architects who can implement a building envelope-first strategy and closely look at material selection to acquire more credit towards LEED v5 certification.
Many of the prerequisite and optional LEED v5 credits, including Carbon Assessment, Minimum Energy Efficiency, Enhanced Energy Efficiency, and Reduce Peak Thermal Loads, require buildings to be designed in alignment with Section 4.2 of ASHRAE 90.1, which outlines compliance paths for envelop design. Projects registering now must comply with the 2019 version whereas those registered after January 1, 2028, must comply with ASHRAE 90.1–2022. Both of these standard versions push projects toward better thermal performance and tighter air leakage thresholds which are key for reducing operational impacts on the environment.
Under the ASHRAE standards, compliance options include a prescriptive path and also a performance path that has envelope backstops. Previously, mechanical HVAC and lighting systems have received much attention when it comes to building performance. However, recent updates in ASHRAE 90.1 and LEED v5 recognize building envelope technologies such as continuous insulation as the foundation to improved operational performance and one of the most effective tools for long-term emissions reduction.
As a result, the guidelines limit value engineering and performance trade-offs that might sacrifice longer life elements such as windows and walls in favor of shorter-life equipment, such as lighting and HVAC systems. Such an approach helps ensure that the building envelope is well-built from the ground up and that the design and analysis of future buildings do not solely rely on powered elements.
For architects pursuing LEED v5 certification, 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. Instead, polyisocyanurate continuous insulation, or Polyiso CI, offers a strategic path to enhanced building performance and multiple credit opportunities.
Polyiso CI insulates the entire opaque exterior of framed walls to reduce energy losses and gains due to thermal bridging. Because polyiso has one of the highest R-values per inch when compared to other insulating products, Polyiso CI delivers excellent thermal performance without the need for bulky, thermally inefficient attachment systems required by other insulation materials.
Additionally, when taped and sealed per manufacturer’s instructions, Polyiso CI can serve as an air and water barrier in the exterior wall and help mitigate air intrusion and condensation issues. This capability helps improve occupant comfort and reduces the possibility of outdoor pollutants and allergens infiltration. Projects utilizing Polyiso CI as an air barrier often undergo blower door testing, which can help them accumulate additional LEED credits under the Reduce Peak Thermal Load category.
Another significant way LEED v5 is driving decarbonization is by requiring project teams to quantify the embodied carbon impacts of the building envelope and hardscape under their Materials and Resources category. Specifically, the rating system mandates the reporting of cradle-to-gate (A1-A3) global warming potential (GWP), for a list of core building materials, including insulation.
A material’s GWP estimates the amount of energy emissions one ton of a certain gas will absorb in a given amount of time, relative to one ton of carbon dioxide (CO2). A substance with a GWP value of one has the same climate impact as CO2. In this context, lower is better. Polyiso products perform exceptionally well on this front as well. They are manufactured with pentane, a hydrocarbon with zero ozone depletion potential and a GWP value well below one.
To support transparency and facilitate requirements by green building certifications such as LEED v5, the Polyisocyanurate Insulation Manufacturer Association has published ISO-compliant Environmental Product Declarations (EPDs) for polyiso products manufactured in North America. These industry-averaged EPDs provide environmental impact information, analyzing the cradle-to-grave life cycle of polyiso products over a 75-year building reference service life, as specified in the Product Category Rule for thermal insulation. In particular, the reports factor in environmental impacts from the supply and transport of raw materials as well as the manufacture, transport, installation, replacement, and disposal of polyiso products.
For Western architects aiming to meet the embodied carbon transparency and reduction goals in LEED v5, polyiso’s favorable environmental profile and robust documentation offer another distinct advantage.
LEED v5 offers a framework that empowers architects to lead with intention, prioritizing building elements that deliver long-term, measurable results. For practitioners across the West, where progressive codes and varying climatic conditions already set a high bar, this next chapter offers an opportunity to not only meet but exceed performance expectations. In doing so, they’re not just checking boxes, they are helping redefine what resilient, carbon-conscious construction looks like in practice.
