Substrates
Fully supported roofs require a decking underneath, the most common material being wood. However, other materials can be used for a substrate provided that clips can be fixed securely. Wall cladding can use either self-supporting copper panels or thinner copper bonded to a substrate. An underlay is recommended separating substrate and copper, which can allow movement in the copper, provide a temporary weathering for the building during construction, deal with irregularities on the substrate surface and offer some sound absorption. Ventilation
Copper is not affected by the underside corrosion which can cause premature failure of most other metal roofing materials and does not require complex ventilation measures. It is therefore entirely suitable for use on either 'warm' (unventilated) or 'cold' (ventilated) roof constructions. For 'warm' roofs, adequate vapour control layers should be properly installed with sufficient insulation. For 'cold' roofs, ventilation in accordance with the Building Regulations is provided by gaps at upper and lower edges of the roof or, if these are not feasible, by formed copper hoods. Special consideration or advice may be needed for areas with high humidity or where air conditioning is to be used: contact the Copper in Architecture Technical Advisor.
Corrosion and Compatibility
The natural electrical potential of copper is comparatively high and it is not affected by other metals on the outside of buildings. However, copper can cause corrosion to some other metals like steel, aluminium or zinc if there is direct contact between the metals and an electrolyte (such as water) is present. Furthermore, if rainwater from copper roofing or cladding runs onto other metals with a lower electrical potential, there may be interaction unless they are protected and maintained by established methods. Metals unaffected by the above are lead, stainless steel and brass. These metals can be joined to copper without any corrosion problems. Rainwater running off bitumen exposed to the sun can cause corrosion problems for various materials including copper. Certain residues washed out of concrete or mortar can cause copper to take on a blue-green colour. Also, the wash-off from red cedar shingles can cause metals to corrode. Lightning Protection
Due to its good electrical conductivity and resistance to corrosion, copper maintains an important role in lightning protection applications. The high conductivity of copper facilitates the rapid transmission of lightning energy, offering the path of least resistance and avoiding damage to a building's fabric. Copper roofs may be used as part of a lightning protection scheme where the copper skin, gutters and rainwater pipes can be linked and bonded to an earth termination facility. The specified thickness of copper is usually adequate for lightning protection and further guidance is available in BS 6651. Needless to say, the old wife's tale that copper roofs and lightning conductors actually attract lightning is not based on fact. |
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