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Natural selection: Zinc's longevity stands the test of time to prepare for the future

With the recent upswing in "green" design and incorporation of everything from

paper cups to commercial buildings, the tendency toward "green washing"-

labeling a product green that in reality is not-has become inevitable as

companies and individuals seek to cash-in on this growing trend.

With that being said, there are quite a few "natural" materials out there that have green characteristics. Zinc is one such product in the areas of roofing and cladding. In addition, zinc has a history as a building material that allows it to substantiate its claims of longevity and sustainability.

Ancient History

The use of zinc as a building material can be traced back to the ruins of Pompeii, Italy, and beyond. Zinc roofing in Europe has decades upon decades of experience and stands today as a lasting tribute to zinc's versatility.

Zinc develops a natural patina. Just as copper turns brown and then green, zinc will go from a shiny mill finish to a uniform gray in the course of two to five years. This patina is a chemical mixture of the zinc with rainwater-forming zinc hydroxide-with the addition of carbon dioxide or pollution that causes the patina to form. It is this natural patina that gives zinc its incredible longevity-usually around 100 years. And it is this longevity that makes zinc roofing and wall cladding one of the most affordable building products over the life of a building.

 

As an example, the average life span of flat roofing materials, depending on the source referenced, is 17 to 25 years. With that statistic in mind, most of these plastic and petroleum-based products will need to be replaced four to five times before an owner would have to consider replacing a comparable low-slope zinc roof. Even painted metals, with impressive 30- to 50-year life spans, cannot hold up to the staying power of zinc's 100- year average life span.

Versatile Choice

In addition, zinc can be perforated, cut and scratched without worrying about rust. This capability relies once again on the natural patina of zinc. This has resulted in more and more projects using zinc. Users can expect perforations of standard zinc profiles to add $1 to $4 per square foot to the cost. With most profiles staying low, around the $5 to $7 per square foot material cost, perforated zinc starts to make much more sense.

"We have seen a real trend toward using the material in this manner," said VM ZINC Project Manager Alex Pittman of Umicore Building Products USA Inc., Raleigh, N.C. "One notable project has been the interior of the Institute for Molecular Medicine in Houston. The architects on that project used the zinc as a perforated scrim in front of the stairwell landings, as well as in other ways. It really is quite dramatic."

The aesthetics of the material ranges from the traditional, such as the mansard roofs of Paris, to the more contemporary, such as the Institute for Molecular Medicine. This ability to bridge multiple styles makes zinc a versatile option from a vast choice of palettes. In the end, without regard to aesthetics or the style of the building, the material will develop a soft, warm gray patina that will slightly change in appearance depending on sky conditions. This makes the product seem alive-which it is when one considers its patina process.

 

Diverse Uses

Zinc has also seen a steady climb in use as a rainscreen and in wall cladding. The natural tendency of moisture to migrate and form in building cavities has dictated a renewed interest and an increased demand for this ancient approach to wall construction. The logic behind such systems states water or moisture will be present in the walls, so instead of trying to seal that moisture or encapsulate it, rainscreens rely on weeps, or screening, at the bottom of the wall, which allow moisture to weep, or drain out, of the naturally ventilated air cavity. Any remaining moisture is mitigated by the airflow within the wall cavity. When combined with breathable but watertight membranes for wall substrates, dew points that were once caught in wall assemblies are now permitted to escape.

Rainscreen approaches to construction have seen resurgence in a variety of materials due also in part to their lack of caulking at critical junctures, such as expansion or control joints. On large projects, caulking is not only a large line item in the construction costs, but it also becomes a maintenance issue for the owner. Eliminating caulking is like eliminating a 10-year material in relationship to a 100-year material-or at least that is the case with zinc. Off-gassing, VOCs and other health concerns can also be somewhat mitigated with the rainscreen approach to wall construction due to a rainscreen's natural chimney or "stack" effect, which pulls air from the bottom of the wall and ventilates it at the top of the wall. This is the same effect that dries out moisture that may have not escaped through the bottom of the wall screening.

 

Green Benefits

Finally, zinc can be recycled at a rate of 90 to 100 percent and has less embodied energy than aluminum or steel. So not only does it use less energy in its production versus that of some other metals, it also has a "second life" after it comes off of the building. Combining a high recycle rate with a low maintenance rate and a long life cycle equating into lower costs is a win-win-win for both architect and owner. This product will not end up in landfills or polluting the countryside once it reaches the end of its useful life. This makes zinc a natural selection for any building product-one that will survive for the long run.

Dan Nicely is director of architectural sales for Umicore Building Products USA Inc., Raleigh, N.C. For more information, go to www.vmzinc-us.com.

www.vmzinc-us.com