Continuous insulation is an everyday presence in the life of many buildings due to its inclusion in ASHRAE 90.1.
As the name implies, continuous insulation is the requirement that no gaps or flaws exist in a buildings’ protection. The idea is that the R-value of the insulation – which Buildings.com simply defines as its thermal performance – is a misleading indicator of the actual comfort and efficiency of the building. Put simply: If doesn’t matter how good the insulation is if energy can easily escape.
The Buildings.com piece, which was posted this week, says that ASHRAE 90.1 mandates use of insulation instead of or in addition to fiberglass batts. The standard – which is “Energy Standard for Buildings Except Low-Rise Residential Buildings” – prescribes that “a continuous insulation installed over the studs, such as rigid foam, must also be applied.” Building.com suggests that expanded polystyrene, extruded polystyrene or polyisocyanurate are good candidates for the job.
Batts aren’t the answer because their discontinuous, segmented nature leads to pathways through the building envelope. Steve Flaten, the Senior Architect at engineering and consulting firm Braun Intertec, suggested that continuous insulation is not only aimed at eliminating the big gaps but to guard against the loss of heat or cooling through elements in the building that can serve as conduit from the inside to the outside:
This technique involves placing a layer of insulation on the exterior of a building to deal with heat loss that results from thermal transfer at studs as a result of conduction. Ultimately, this technique attempts to improve the overall insulation value of walls.
This week, The Altus Group released a technology brief on ASHRAE 90.1. It says that local jurisdictions can amend the standard and that compliance details vary between eight climate areas in the United States. The standard also can change over time. The bottom line of the piece is clear. A continuous insulation barrier is a very big deal:
High building envelope air leakage often is the primary energy efficiency failure in modern construction. While conductive, convective and radiative heat loss/gain can be considerable, mass transfer of unconditioned air in a poorly sealed envelope will overwhelm them all.
In addition to saving money by improving insulation, continuous insulation safeguards the health of the people within the structure. Dow Chemical says that the use of the technique moves the dew point from inside to outside the wall cavity. This lowers the risk of condensation, which is a prime ingredient for the growth of mold and mildew.
An interesting note is that the use of continuous insulation may subtly change the materials used in building construction and retrofits. An article at Inside Self Storage earlier this month suggests that the attraction of load bearing masonry within continuously insulated buildings may be fading, at least for factories, industrial facilities and other active sites where damage is fairly common.
Masonry is energy efficient and worthwhile in buildings in which temperatures vary greatly. It is, however, expensive to repair compared to other materials that can be used. If continuous insulation and generally more stringent energy codes are in effect, the inherent efficiency of the materials is less important. In such cases, the price tag of repairs takes precedence and less expensive/less efficient materials favored.
The benefits of continuous insulation are great. It saves money, improves the comfort and health of those within the building and can lead to somewhat lower construction costs. Of course, it is important to follow all applicable rules, regulations and best practices when planning a new building. It also is a good idea to implement continuous insulation strategies whenever walls are open for upgrades and updates.