A Look at Building Envelope: the 4Ws of Optimizing Energy Efficiency with Continuous Insulation
Continuous insulation (CI) has established itself as an industry standard practice that contributes to optimum building performance; and in most regions, CI is raising the bar on energy efficiency and high-performance solutions for buildings.
As defined by the U.S. Department of Energy and model building codes, “continuous insulation” is insulation that runs continuously over structural members and is free of significant thermal bridging. It is installed on the interior or exterior, and it is integral to any opaque surface of the building envelope.
As building codes and requirements continue to trend toward greater attention to higher efficiency requirements, energy conservation professionals, building designers, code bodies, and contractors are recognizing how increased use of different kinds of insulation materials for multiple applications improves performance of a building. To better explain how CI enhances the energy efficiency of wall systems, here is the why, what, where, and when.
WHY: Using CI to Increase Energy Efficiency in Wall Systems
Although CI can serve a number of different roles when incorporated into a building structure, most importantly, it eliminates or greatly reduces the existence of thermal bridges. Thermal bridging occurs when a material with a high thermal conductivity, such as wood, steel, or masonry structural elements, allows an easy pathway for heat flow across the thermal envelope. Thermal bridging in buildings can reduce energy efficiency, create indoor heating and/or cooling problems, and even lead to condensation issues. Reducing the risk of thermal bridging not only cuts down on energy costs and increases comfort, but also can reduce condensation that could cause mold, rot, and rust, and harm indoor air quality.
The most common thermal bridges, addressed by most codes, involve thermal bridging through framing. Although steel is the most obvious offender, wood framing also can hurt wall thermal performance. For example, in a typical framed wall, framing can easily account for 25% or more of the wall area, allowing heat to flow easily through the structure to the outdoors or connected unconditioned spaces and reduce energy efficiency of conditioned building envelope spaces.
Other structures, such as balconies, slab edges, awnings, or porte cocheres, have
elements that also can contribute to thermal bridging. These can be effective in conducting the heating or cooling energy out of a building and ejecting it into the surrounding air, resulting in high space conditioning costs and undesirably cold or warm floors.
Are there other benefits of CI? Certain CI materials also can act as air barriers and water-resistive barriers when correctly integrated with window and door details. Other materials can satisfy structural, green building, or fire requirements, while also addressing practical needs such as cladding installation.
WHAT: The Right Product Mix for
Optimal Wall Performance
Determining the proper amount and type of CI to use for a given project might seem challenging, especially when considering how the overall insulation and air
barrier system can help manage condensation and heat transfer.
When selecting the product that will best achieve your CI goals, thickness is often a critical consideration. Multiple kinds of insulation materials are used for CI: glass fiber, rock fiber, and rigid plastic foams may be employed for CI, for example. As CI materials get thicker (to meet code requirements), wall cross-section dimensions grow. This need for increased thicknesses can lead to other adjustments required in the project, including fastener length, cladding attachments, and integration with flashings and door and window jambs. A strategy that the design professional can employ to avoid the need for some of these modified materials and practices is to identify products that meet the building design and code requirements, using a minimum thickness.
One option is to incorporate foam plastic insulating sheathing, a widely used and cost-effective product, into the wall assembly. There are also other material options for continuous insulation, such as closed-cell spray polyurethane foam and semi-rigid mineral fiber boards. Due to its high thermal performance, polyisocyanurate (polyiso) foam is commonly used by professionals who have the goal of maximizing thermal efficiency while considering the space allocated for building envelope wall cross-sectional thickness, building owners interested in maximizing energy savings for the investment in facilities, and homebuilders working to meet more stringent energy conservation codes cost effectively. With one of the highest R-values per inch, polyiso foam is an excellent choice for achieving thermal efficiency. It has a low tendency to absorb moisture, is solvent resistant, provides strong dimensional stability, and meets typical fire performance requirements for exterior building shell materials. When seams are taped, penetrations sealed, and the system is integrated with window and door flashings, polyiso foam sheathing also can create an effective air and water-resistive barrier, eliminating the need for a separate building wrap.
Another effective CI option is to install closed-cell spray polyurethane foam (ccSPF) on the exterior of the building envelope. When integrated with window and door flashings, exterior ccSPF can provide CI, air barrier, water-resistive barrier, and vapor-retarder functions in one installation step.
Once the type of CI product is determined, it is important to consider the other insulation, air-sealing, and moisture-management strategies that will be implemented. Products like fiber glass, mineral wool, and spray foam work together with a CI material to ensure long-term energy efficiency. Combined with a proper installation, the right mix of products will determine whether or not the structure will deliver a durable, long-lasting performance.
WHERE: The Impact of Location and Climate on Wall Performance
Installing the right mix of insulation products in the building depends on where and how in the structure CI will be installed, what total assembly R-values or U-values are desired, and the climate where the project is located. The consideration of acoustical comfort should be considered as well. In buildings near high noise-generating facilities—like rail, truck, or air transportation facilities; major traffic thoroughfares; or noisy industrial installations—it is desirable to limit sound transmission into the occupied space. Certain CI materials can help limit the intrusion of noise into occupied spaces and should be reviewed for their ability to contribute to that sound energy transmission reduction. Some materials can reduce reflected sound energy, as might be experienced in buildings that are closely spaced, with sound reflecting from one wall to the opposite wall.
Understanding which energy-efficiency standards (like LEED or ASHRAE High Performance Buildings) and more stringent building codes (such as the International Green Construction Code) are in place is crucial in determining how to provide a CI component in the project. For the current status of energy codes and standards adopted by each state, visit energycodes.gov or iccsafe.org.
CI will have the biggest impact on reducing energy losses when applied to the entire building structure, eliminating thermal bridging through the roof, walls, and foundation.
Consider installing CI throughout the structure to provide energy, moisture, and air infiltration control; protect the building’s exterior; and increase energy efficiency.
WHEN: Collaborating with Teams to Incorporate CI
Collaborate with project partners early in the design and construction process to agree on the best overall insulation, air-sealing, and moisture-management strategy including CI. This will help the team avoid costly oversights or decreased building energy efficiency and occupant comfort.
Learn early in the project stages about planned designs. Recommend improvements to the wall, roof, and floor assemblies; and an effective product mix for the project. Once a design is finalized, be sure to communicate what other trades (such as framers or window installers) need to do to help ensure a successful CI installation later in the process.
As building codes and sustainability desires drive higher energy efficiency, CI can play a crucial role in meeting or exceeding code-required R-values or U-factors when used in conjunction with traditional insulation methods.
Although CI is seen as an affordable or economical option to enhance energy savings at the point of construction, the benefits of a proper building envelope go beyond project savings. As the boundary between the interior and exterior, the building envelope provides outdoor protection and indoor comfort, adding value to the building and saving the owner money in the future.
For all these reasons, CI has become a mainstream concept and code-required feature that should be considered when determining a cost-effective and long-term solution for eliminating thermal bridges and maximizing a building’s energy efficiency, comfort, and performance.