by Brian Chang
Growing use of continuous insulation (CI) across virtually all building types reflects its role as an essential means to achieving higher efficiency standards as well as sustainability goals. It also affects the design process. Applying CI demands that specifiers master this construction element, taking time to consider how to make the best possible choice for a given building project.
Basic but essential questions have sown confusion among too many project teams. For example, how much insulation is sufficient? And how much is too much? What is the best way to calculate the cost-effectiveness of the CI product system—is it lowest life-cycle cost? These are just a couple of criteria for evaluating and selecting the so-called ‘building blanket,’ but there are others, and the complexity only grows.
Essential to the application criteria and project decision-making, of course, are the other envelope requirements—the choice of cladding, configurations of air and moisture barriers, and window-to-wall ratio, among others. Depending on the jurisdiction, certain code mandates (and even utility or zoning incentives) should be factored into the decision. Also important is the type of CI. There are many choices of product, materials, and systems, but which offers the best match for a particular project?
Four specifier hurdles
Several factors help demystify the continuous insulation approach, establishing a coherent methodology for choosing the right CI solution. It begins with four essential requirements every specifier should review.
Performance requirements
Continuous insulation is identified thusly in American Society of Heating, Refrigerating, and Air-conditioning Engineers (ASHRAE) 90.1-2013, Energy Standard for Buildings Except Low-rise Residential Buildings:
uncompressed and continuous across all structural members without thermal bridges other than fasteners and service openings.
Per ASHRAE, CI can be installed on the enclosure’s exterior or interior, or it can be integral to opaque envelope materials. Wherever it is located, the CI layer must span across or through thermally conductive elements such as steel columns, metal studs, concrete masonry units (CMUs), and others. If not, thermal bridging through high-conductivity structural components can reduce insulation performance by up to 40 to 60 percent in metal-framed buildings, and up to 20 percent in wood-framed enclosures, according to studies by Oak Ridge National Laboratories (ORNL). (For more, see “A Review of High R-value Wood-framed and Composite Wood Wall Technologies Using Advanced Insulation Techniques,” by Jan Kosny, Andi Asiz, Ian Smith, Som Shrestha, and Ali Fallahi. It appeared in Energy and Buildings [72], published in 2014 by Elsevier.)
Thermal bridges have other detrimental effects. Most noteworthy, these hot and cold spots can cause condensation and moisture ingress in the enclosure, as well as occupant discomfort in localized interior spaces. Clearly, traditional insulation layers—for decades located neatly between steel columns or light-gauge studs—have been insufficient.
