Engineering, by Code and by Practice

Suitable design and specification of metal claddings is just as important as their proper engineering, manufacture, fabrication, and application by experienced construction teams. With the range of products available, this presents a key to building design: Metal roof and wall solutions on the market today include engineered solutions such as single-skin metal panels for metal roof and metal wall applications, IMPs, and related roofing systems including the standing-seam metal systems. They can be applied extensively in the architectural, commercial, institutional, and residential markets, but also those industrial and agricultural settings that helped seed their wider use.

A number of codes and standards provide essential knowledge and minimum requirements for the use of metal envelope systems. In addition to manufacturer recommendations and their model specifications, which reference many of the key rules, the International Building Code (IBC) and standards developed by groups including the Metal Building Manufacturers Association (MBMA) are most valuable to architects.

Because IMPs and other insulated metal-skin assemblies are valued for their energy performance, a number of key references are found within Department of Energy (DOE) recommendations and the prescriptive and performance paths given in the ASHRAE Standard 90.1 and the International Energy Conservation Code (IECC), which has been updated to its 2009 version in many jurisdictions and now has an even more rigorous 2012 version. By now, most states and many jurisdictions have adopted a recent version of ASHRAE 90.1 or the IECC as a minimum, which include such prescriptive requirements as:

• Fenestration limited to 40% of vertical envelope.

• CI for all buildings with steel frames (in climate zones 3-8).

• Use of air barriers and means to seal all wall joints and through-envelope penetrations.

There are other important requirements also.

Yet, one of the benefits of IMPs and insulated metal panel cladding systems is that they meet the above “big three” rules. The insulation is continuous when applied as a barrier wall and the CI is typically exterior to vertical structural elements, such as columns and girts. (This eliminates thermal bridging through steel columns and metal framing, for example.) The metal skins also serve as a highly effective air barrier; last, these opaque claddings help offset the solar heat-gain coefficient (SHGC) of the glazed area.

All these traits also help the design team meet prescriptive R-values or the minimums given in the IECC's Table C402.2 for both CI values and the façade U-factor, defined as how fast heat moves out of or into a building through the enclosure. U-factor is beneficial as a measure of total wall performance rather than using multiple prescriptive or performance measures. Panelized metal construction is often employed as a means to achieve a desired U-factor to meet ASHRAE 90.1 or IECC, or both.