Delivering an energy-efficient, high-performance structure requires a comprehensive approach to building design. This, of course, includes careful consideration of the building products and systems used on a project. But here’s the thing; this careful consideration extends beyond what you see when you look at a building (picture those striking metal roof and wall panels) and must also include the insulation underneath.
Many building designers specify polyisocyanurate (polyiso) insulation, which is a closed-cell, rigid foam board insulation. It can be used across the entire building envelope to increase its thermal performance and energy efficiency. Polyiso is synonymous with having one of the highest R-values per inch compared to other insulation products, including mineral wool insulation. The effectiveness of the insulation solution makes it possible for project teams to meet required R-values without building up extra layers of materials in building envelope systems. But let’s dig deeper. What are some of the real-world factors that can impact a product’s insulating power?
First, let’s set the stage: Thermal resistance, or R-value, is a measurement of how building envelope materials like insulation will resist heat flow in a static test environment. However, real-world applications will differ from laboratory circumstances. The insulation used in an exterior wall will be part of the overall building envelope, not used in isolation. This means that real-world factors such as moisture, air infiltration, and convective flows within the building envelope cavities can play a part in the overall thermal efficiency of a structure.
Closed-cell foam insulation solutions like polyiso derive their R-value from the low-global warming potential (GWP) blowing agents/gases contained within the cells. The blowing agents for different types of foam plastics will vary, but all are selected for their ability to enhance the thermal performance of the foam. Because of its closed-cell composition, polyiso provides excellent resistance to moisture and air intrusion along with increased thermal performance.
On the other hand, fibrous materials like mineral wool insulation derive their R-value from air trapped within pockets between the fibers. Air and/or water movement through fibrous insulation products will reduce their insulating power, which is why fibrous insulations have traditionally been used within interior stud cavities in walls, which restricts air and water movement on all six sides of the cavity.
To illustrate how fibrous products like mineral wool insulation work, imagine wearing a sweater outside on a cool day to keep warm. On a mild day, the sweater does a decent job keeping you comfortable. But if the wind picks up, the air penetrates the fibers and the sweater no longer insulates the way it did when the air was still. If it rains, the sweater gets wet as water penetrates the fibers, again impacting the insulating power. When the sweater dries out, it will insulate well again, but how long will it take to dry? What if you live in a location where rain and wind is the norm? In such conditions, we doubt that a sweater would be your first choice of clothing to keep you warm.
Closed-cell foam insulation products like polyiso provide excellent resistance to moisture and air intrusion along with increased thermal performance, while fibrous materials do not. Tech bulletins or FAQs from fibrous insulation manufacturers state that when product is wet, R-value will be reduced, but they do not typically reference how much reduction will be seen. It’s not worth finding out… after all, why risk the performance of the building?
To leverage the proven insulating power of polyiso, building design teams can turn to Defend-R from Drexel Metals, an all-in-one building solution. Defend-R is a complete line of roof and wall insulation panels that feature a closed-cell polyiso foam core manufactured to various facer types to meet project needs. Drexel Metals offers a complete system approach to roof and wall assemblies because we are backed by Carlisle, whose years of experience in polyiso manufacturing and moisture and vapor barriers is invaluable. We’ve leveraged that product category experience to give our customers the highest-quality insulation solutions for their next project.
