What is CI?
The past 20 years has seen a radical shift in the use of Continuous Insulation in the commercial construction building sector. So what is Continuous Insulation, or CI, as it’s commonly called? Continuous Insulation is defined by ASHRAE as:
“Insulation that is uncompressed and continuous across all structural members without thermal bridges other than fasteners and service openings. It is installed on the interior, exterior, or is integral to any opaque surface of the building envelope.”
A common analogy often used to explain a more simplistic theory of CI references the use of a winter coat when you go outside. If you wear your coat on a cold winter day but leave front unzipped and open, your body heat quickly escapes, and you feel the cold. It doesn’t matter how thick your coat is if it’s not continuous around your body. As soon as you zip it completely up, the effectiveness of the coat ‘blanketing’ your core yields a tremendous difference in comfort. CI is similar in the fact that it is thought of as ‘blanketing’ your building, effectively covering up all the short circuit thermal bridges and gaps that exist due to structural members or transitions in assemblies.
Since CI was first introduced into ASHRAE 90.1 in 1999, the prescriptive requirement for CI has steadily increased in R-values as well as spread to all climate zones. So why has CI become so prevalent in the building code requirements? The use of CI began to gain traction in the United States in the early 2000’s as the awareness and need for more energy efficient buildings and reduced fossil fuel usage gained popularity and momentum. As a result, in 2007 the ASHRAE adopted the 2030 Challenge. This targeted the goal that all new buildings, developments, and major renovations would strive to be carbon neutral, meaning no fossil fuel or greenhouse gas emitting energy was needed to operate the building, by 2030. As revisions and updates to the new ASHRAE standards have been issued, the use and required amounts of CI has continued to increase.
Continuous Insulation can be used on nearly all types of building design, from common metal-framed and masonry walls, to cement plaster, architectural metal panel systems, rainscreens, and EIFS. CI can even be incorporated into pre-built panelized construction and pre-cast concrete tilt-up construction. In most building designs, it is easiest to incorporate CI on the outboard side of the exterior framing. In these applications, there is far less complicated detailing required in order to maintain continuity of the CI. There are certain systems, like tilt-up and pre-cast where the only option, and sometimes the best option, might be to have the CI on the interior side of the wall.
One of the primary benefits of CI is how it impacts the dew point of the wall assembly. When CI is located on the outward side of the structural framing, it significantly reduces the thermal bridging effecti on the metal stud framing. This helps maintain the temperature of the metal stud framing much closer to the interior building temperature, which in turn significantly increases the efficiency and effectiveness of the stud cavity insulation. Studies by ASHRAE have proven that the R-value of stud cavity insulation can be reduced by up to 63% when no CI is used, and thermal bridging impacts the metal stud framing.
Outboard CI also reduces the likelihood of moisture accumulating within the walls by moving the theoretical dew point outside of the framing, and thus outside the water barrier. When insulation is installed only inside the framing cavities without CI on the exterior, it typically forces the dew point of the assembly to fall within the insulation of the wall stud cavities. This can significantly increase the risk of condensation, and ultimately, moisture accumulation within the wall.
Properly designing CI into the wall assemblies can greatly reduce the potential for moisture accumulation, but only via vapor diffusion. Air movement, however, can carry up to 1000 times more moisture than what is transferred through diffusion. Therefore, it is critical that a robust air barrier system be incorporated and aligned with the CI, whether this is achieved integrally to the CI or separately with a standalone air barrier system. Air movement within the wall assemblies can minimize any value provided by CI so the combination of the systems must be accounted for to maintain a high-performance building.
CI can come in many different types of products with varying performance characteristics. Common forms of CI include Spray Polyurethane Foam (SPF), Extruded Polystyrene (XPS), Polyisocyanurate (Iso), and Fiberboard/Mineral Wool. Each product offers different thermal resistance values, air and water permeance ratings, different fire characteristics, along with many other variables. Not every product is ideal for each application. It’s important to understand what type of performance factors are needed from your CI to determine which type of product is the best fit. It’s also extremely important to understand how your CI transitions to the other building envelope systems, like windows, doors, curtain walls, and roof systems. How do you ensure you are maintaining your thermal layer as well as your air, water, and vapor continuity? All of these factors are critical in order to ensure you have a high-performance building.
CI is more prevalent and demanded than ever before. It is becoming glaringly obvious to designers, engineers, contractors, and owners that its role in the envelope system is essential to a comfortable, safe, and energy-efficient building. The factors and considerations for designing and selecting the right materials and applications are increasingly challenging. Understanding the limitations and characteristics of all components of the wall assemblies and how they interact, compliment, or contradict each other is extremely critical but necessary to create that high-performance building envelope system.
To learn more about Continuous Insulation and the details of the different product options and applications, come to the BEC Indiana event on February 11, 2020.