There are two important factors to remember when designing or installing any copper or copper-alloy systems. The first concerns compatible building materials, and the second is how to address expansion and contraction. They can determine the success of a copper installation, especially outdoors, but also for interior projects.
Not all metals and materials are compatible. If incompatible (dissimilar) metals are placed in contact, and there is moisture and oxygen present, galvanic corrosion can occur. It can cause dissolution, and eventually failure of the less noble metal in the couple. Sometimes dissimilar metals together if the right details are followed, such as providing a separator. Options here include distance as a separator or another material. If another material is considered, make sure it is compatible with both metals. If you have questions about a metal's compatibility with copper or a copper alloy, consult the CCBDA.
This nobility chart lists some of the more common metals used in architecture. The higher the metal is ranked on the chart the more noble
or cathodic it is. This means its potential for galvanic corrosion is low. The lower the metal is ranked on the chart the less noble or more
anodic it is. Its potential for attack by galvanic corrosion is much greater. For example you may use copper with lead because they are
ranked close on the chart. The further the spread from copper, coming down the chart, the more serious the situation is, and the greater the
risk of galvanic corrosion. In a copper-aluminum couple, for example, the aluminum will be rapidly attacked under galvanic corrosion conditions.
It must be strongly emphasized that the type of fasteners used with copper must also be compatible with copper. Otherwise galvanic corrosion and failure will occur. With copper and copper alloys the following fasteners work well:
- Copper roofing and sheet metal nails. Ring shank nails have more holding power.
- Brass and bronze screws and fasteners.
- Stainless steel fasteners, typically alloys 304 & 316.
Do not use the following with copper:
- Steel nails and fasteners.
- Galvanized steel nails and fasteners.
- Aluminum nails and fasteners.
Expansion & Contraction
The expansion and contraction of copper, as well as that of any other adjacent material, is a function of variations in temperature, which is obviously less a concern for interior than exterior projects. However, the temperature during installation can play an important role, since
future thermal expansion and contraction will occur as the temperature rises and falls relative to this initial value. This is particularly important when installing components with potential restrictions to movement in one direction.
It is very important that a copper system be designed to allow for the expected amount of expansion and contraction. For example, in some systems, movement can appear as oil-canning of copper panels. This is usually aesthetically objectionable, and the oil-canning may be
minimized by the use of expansion cleats, and by limiting the use of fixed cleats to pans 10-feet (3 m) maximum in length.
Whatever the type of installation the architect or designer specifies, care should be taken to insure that the natural movement the copper
will undergo daily is not restricted or hampered in such a way as to cause degradation in the appearance of the installation, or eventual failure
of the system in extreme cases.
When using copper alloys, adequate allowances must also be made for expansion and contraction. Coefficients for calculating allowances
for different alloys can be obtained from the CCBDA.