Benefits of zinc make it popular cladding
What is the first metal that you think of when considering
design options for a new standing-seam roof or wall panel system?
Are steel and aluminum your primary choices, or do you lean more
towards exotic metals such as copper or stainless steel? When was
the last time you considered zinc? Its manufacturability and
resistance to weathering are only a few of the benefits of this
beautiful metal that are driving the increasing popularity of zinc
for building cladding.
The physical properties of zinc make it a very unique and useful
material to be used as building cladding. Many of us are familiar
with the oxidation process of steel, which forms rust. Steel will
continue to corrode when rust is present on its surface, eventually
rendering it unusable. Zinc, on the other hand, has the ability to
resist continued corrosion due to a very unique reaction. When zinc
is exposed to the moisture and carbon dioxide that is present in
our atmosphere, a protective layer of zinc carbonate forms on its
surface, prohibiting the corrosion process that steel experiences.
The resulting zinc-carbonate layer creates a beautiful bluish
patina for a very desirable appearance.
In addition to its beauty, this protective barrier provides
longevity that will allow zinc to protect a building's exterior for
years to come. It is not uncommon for a properly designed zinc roof
or wall panel system to last over 60 years in most climatic
conditions. Another unique characteristic of zinc is that it can
"heal" itself overtime. As it continues to patina throughout its
life, scratches and imperfections that were once present will
There are however certain conditions that will prohibit the
protective patina from forming. If zinc is exposed to moisture,
from humidity, condensation or even submersion in water without the
presence of carbon dioxide, white rust will form. Just as with rust
on the steel surface, this white rust will continue to deteriorate
zinc. This condition can occur on the backside or underside of a
zinc panel that is not exposed to the exterior environment where
carbon dioxide is prevalent. To prevent the white rust from
forming, the backside or underside of a standing-seam roof panel or
wall panel, or the interior side of a gutter, should be always be
coated to prevent deterioration of the zinc. Ventilation should
also be provided behind panels to promote air flow that will move
away any moisture that may accumulate due to condensation.
Clean and Green
Zinc is also a very environmentally friendly metal for a number
of reasons. It is a 100 percent recyclable metal that can be reused
over and over again. Zinc is also a fungistat, which is an agent
that prohibits the reproduction of mold, mildew and fungus. This
can greatly reduce the risk of moss or even black mold from forming
on the exterior of a building in areas that are in contact with the
metal. Interestingly, the rainwater run-off from zinc is clean,
unlike the rainwater run-off from other metals such as copper,
which is a fungicide. However, in addition to killing fungus,
fungicides can also kill vegetation. So zinc, unlike copper and
other metals, can be used in areas where vegetation is present, as
it will not damage or compromise plant growth.
Zinc is a very soft and malleable metal that can be formed into
desirable shapes with ease. This characteristic allows zinc to be
used for a wide range of unique architectural applications.
However, it should be noted that zinc becomes much more brittle
when exposed to temperatures below 50 F. Forming zinc in
temperatures this low will cause it to rupture very easily.
Therefore, it is not recommended to break, form or install zinc
panels or trim components in cold weather. Even mechanically
seaming a standingseam roof in cold temperatures can cause the seam
cap or seam legs to crack, rupture or split. If the installer is
unsure of the temperature, it is recommended that the surface
temperature of the zinc material be measured with an infrared
thermometer to assure it is above 50 F.
Thermal Expansion and
With all standing-seam metal roofs, regardless of the material
used, it is important to allow for unlimited thermal movement so
that the panel can expand and contract without restriction. It is
especially critical to allow for sufficient thermal movement for
zinc panels, as it can expand over twice the distance of a steel
panel. Zinc will actually expand almost an entire inch for every 30
feet of panel when exposed to a temperature differential of 160 F,
which is very common throughout much of the United States. If the
panel is restricted by the clip or fasteners when the expansion or
contraction of the metal occurs, the panel will buckle and billow.
This will increase the oil canning effect that is more prevalent in
standing-seam panels that have been improperly installed.
Restricting the movement of the panels will also cause the sealants
that help make the system watertight to break down over time. Trim
components should also be given approximately 1/4-inch at end laps
to allow for thermal expansion.
corrosion also needs to be considered when designing zinc panel or
trim applications. Galvanic corrosion occurs when two dissimilar
metals with a high electric potential between the two are in
contact with each other in the presence of an aqueous solution. The
higher the electric potential between the metals, the more severe
the galvanic reaction will be. Referencing a galvanic corrosion
chart will give you a good idea of which metals will react with
each other. The further apart these metals are on the chart, the
larger the electric potential will be. The effects of galvanic
corrosion are much less severe when metals that are close to each
other on the chart are in contact with each other.
Viewing the accompanying chart, it is clear that bare zinc
should not be placed in contact with metals such as copper or
non-galvanized or unprotected iron. However, zinc can come into
contact with aluminum and galvanized steel with minimal galvanic
It is also critical that zinc not be installed in locations that
will receive rainwater runoff from dissimilar metals. The runoff
will carry electrically charged ions from the metal that will cause
galvanic corrosion of the zinc. If zinc will be in contact with a
dissimilar metal after installation, it is imperative that the two
metals be separated. Protecting the surface of the zinc with a
plastisol coating will help to eliminate the risk of galvanic
reaction from occurring.
Other considerations that need to be taken into account when
designing zinc applications include the risk of deterioration due
to abrasive or corrosive chemicals. Zinc should not be installed
near salt water coasts that receive little or no rainfall, as the
salt spray in the atmosphere can have a damaging effect on the
unprotected zinc material if it is not frequently washed away by
Unprotected zinc should not be in direct contact with acidic
woods such as oak, birch or cedar. Other woods such as pine, spruce
and poplar have a lower acidity and are less abrasive. If zinc is
in contact with an acidic wood, it should be protected with a
Concrete and felts hold moisture that can damage bare zinc in
enclosed areas where carbon dioxide is not present. If zinc will be
in contact with bituminous felts or concrete, it is recommended
that the zinc be protected with a coating. It is also recommended
that the area between the zinc and concrete be ventilated to
promote good air flow.
Protective gloves and long sleeves should be worn when
installing zinc to prevent bare skin from contacting the panels.
Oils in the skin that contact bare zinc can create undesirable
marks. While these marks will disappear over time, it will create
an unsightly blemish on a newly installed panel. A strippable clear
film should be applied to zinc to help protect it during shipping,
handling and installation, and should not be removed until the
panels are installed and all finish work is complete.
When installed properly and appropriate considerations are taken
to assure its surrounding are suitable, zinc is an aesthetically
pleasing, long-lasting and beneficial alternative for building
cladding. Very few metals, practical for use in building design,
offer such an attractive array of characteristics, making zinc an
easy choice for many designers. Its architectural appeal is
continually growing as more designers are realizing the benefits of
this beautiful metal. So whether you are an owner, designer or
contractor, the next time you are faced with an opportunity to
specify metal, think zinc!
Tom Diamond, E.I., is a product engineer for Garland
Industries, a Cleveland, Ohio-based manufacturer and
distributor of high-performance solutions for the
commercial building envelope. In that capacity, he designs
optimum performance metal roof and wall panel systems and
oversees metal system building code compliance at the
national, state and local levels. As a member of
Garland's Speakers Bureau, Diamond presents
educational seminars on how to implement edge metal
designs for code compliance. Visit www.garlandco.com
for more information.