Continuous Insulation – Part 1
This series of posts is definitely for my architecture/construction readers, unless you’re so inclined . . .
As most design professionals know, everything in the field of construction is moving to create more energy efficient buildings. At first, this was a fringe movement that led to standards such as the LEED program developed by the U.S. Green Building Council (USGBC). As the movement has gained momentum, more and more of the standards are becoming a part of local building codes. Certain jurisdictions are requiring some level of LEED certification for buildings. Locally, the City of Baltimore has developed their own Green Buildings Standards as a requirement or alternative to LEED.
Additionally, the International Code Council has begun implementing more “Green” building practices into their family of codes. First, they introduced the “International Energy Conservation Code.” Now, they are working on an “International Green Building Code.”
With the 2009 editions of the International Energy Conservation Code (IECC), one particular requirement has raised significant questions and problems within the building envelope. This term called “Continuous Insulation,” often just a little “ci” in the codes is beginning to make a stir and, if implemented properly, will change the way we build . . . but it is RARELY implemented properly at this point in time . . . and thus this series of posts.
First – what is Continuous Insulation, and why is it such a big deal?
Let’s begin with the second half of the question . . . While CI is used in a variety of wall assemblies, it is most important where materials of high-conductivity are used . . . especially metal. For instance, historically, we would install batt insulation between metal studs and move on. However, in a metal stud wall, the studs conduct so much heat, they reduce the total R-Value by about 50% (depending on specific factors). So your average stud wall (4″-6″ studs) results in a maximum R-value in the R-7 to R-9 range. If CI is used and installed properly, you get approximately the true R-Value of the material. So what is it?
The IECC 2009 actually does not define the term, but they pulled it from ASHRAE 90.1. ASHRAE 90.1 defines Continuous Insulation as insulation that is 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.
With further research, you discover that “fasteners” is meant to include screws, bolts, nails, and the like, but not much else. This means furring strips, clip angles, and other large connectors are generally excluded . . . which is where the big problem lies, and why I spent time doing the research.
If you are using a self-supporting cladding such as brick or other masonry, you can use a system of ties that meets the “fastener” requirement and move on. If you are using a continuously insulating system, such as Insulated Metal Panels or EIFS, you also don’t have a problem (provided they truly are continuous and without thermal bridges). But for any cladding material supported by the building structure, significant problems occur.
For most regions of the country, the IECC 2009 is now requiring R-7.5 or more of CI on metal-framed buildings. In general, this will be 1.5″ or more of insulating material (depending on the specific material used). However, most Cladding Systems, such as Metal Panels, Cementious Siding, etc are only approved for attachment through 1″ of non-supporting material.
If you go to most of these cladding companies’ web sites to find out how to install their product over a thicker insulating layer . . . you will almost universally find a detail similar to the one shown here, which has a metal Z-purlin passing through the supposedly Continuous Insulation to get to the structure. Some suggest using a “Thermal Break” at the connection to the structure. From the research I’ve found, you have still reduced the effectiveness of the CI from between 25%-50%.
As a result, I spent 3 days calling various cladding manufacturers, rigid insulation board manufacturers, and several other industry-related people, while doing online research, code analysis, and more . . . And I finally have some true and good solutions . . . so we’ll pick up there in the next post.
Feel free to contact me at Curry Architects if you need design help in any way.