METAL WALL RETROFIT CONSIDERATIONS

While roofing systems are generally prone to water issues, it is essential to waterproof metal cladding systems as well.

One approach which metal cladding is well suited for is rainscreen design. Ideally, the vapor barrier is placed directly on the exterior side of a substrate, such as sheathing, concrete masonry, or cast-in-place concrete, according to Jeffrey Murphy, FAIA, partner, MBB, New York.

“Rigid or sprayed-on insulation is applied over the vapor barrier, and metal cladding is installed over the insulation on a system of girts, preferably with thermal breaks, tied back to the substrate. The metal cladding serves to intercept wind-driven rain and protect the insulation from damaging ultraviolet solar radiation,” he says.

While this type of an exterior wall assembly is more costly than simply applying cladding panels over an insulated wall cavity, he explains that it offers the highest performance and is effective in all climate zones.

Generally speaking, Andy Feth, PE, DBIA, LEED AP, project executive, C.W. Driver Companies, San Diego, advises that anything mounted on the face of the existing building envelope be removed before the new cladding installation. Also, any penetrations through the existing building envelope should be inspected and sealed prior to installing the new cladding. “The waterproofing barrier occurs underneath the new cladding, so this is where the attention to detail is spent. If greater thermal performance is desired, furring and rigid insulation can be installed prior to the cladding.”

As alluded to here, another key issue with cladding systems is ensuring good thermal performance.

“Thermal performance is of utmost importance in today’s energy-conscious world, and doing it correctly can help save on energy costs,” emphasizes Alex Getelman, executive managing director, MBI Group, New York.

For starters, for systems that require it, he directs project teams to make sure the skin is attached and caulked correctly. “However you attach the skin—it can be clipped, screwed, or tacked—you want to make sure the seams are properly overlaid.”

Another option is insulated metal panels, which, in addition to good thermal insulation, may deliver an all-in-one air, vapor, and water barrier. Otherwise, traditional sheet metal fabrication is dependent on the backup wall construction for thermal performance.

“That typically means that the insulation is located on the interior side of the backup construction or is sprayed on the exterior and protected by the application of the metal panels,” states Alex Adkins, associate principal, DiMella Shaffer, Boston.

Typically, the system requires the expertise of multiple trades, including carpenters, and waterproofing. While installation is generally less expensive because there is more competition, the involvement of multiple trades makes coordination essential.

On the topic of aesthetics, there are many options for material choice, system choice, and color choice, according to Adkins. While designs are often dictated by proportion and massing of the existing materials, as well as the region/neighborhood of the building, Adkins outlines the following three design approaches for metal cladding retrofits:

• Highly machined and very cleanly detailed manufactured panels that contrast with the older existing handcrafted materials. In this approach, the new metal system is fabricated off-site to ensure a highly regular, machined-precision quality, and through this level of detail, it then contrasts with existing masonry or stone work that is manually installed and contains inherent inconsistencies, hence the term “handcrafted.” Color coatings are highly consistent, if desired, or can be manipulated to suggest patterns or materials. This approach might best reinforce a program goal to clearly advertise the contrast between the new use or investment in an older structure.
• Traditional sheet metal roofing/siding materials that are used in nontraditional applications. Essentially a new use for an existing building, this method also allows for continuation of the inconsistencies of handcrafted construction. The use of sheet copper siding, zinc siding, or even steel that develops a rust patina are some examples. The size of the paneling, the pattern of the panels, and the extent of the metal panel system can signal that there is a new use or a new investment while remaining true to the building’s history.
• Traditional sheet metal roofing and siding that are used traditionally. This approach is usually only recommended for a historic repair or restoration where the original metal work is available for highly accurate reproduction. Replication of historic fabric is extremely difficult to successfully achieve, which is why the U.S. Secretary of the Interior historic restoration guidelines do not encourage it.