Roofing and Flashing

The use of lead for roofing dates back hundreds of years, and has been used under all sorts of climatic conditions. In addition to being a common roofing material on many buildings erected centuries ago, lead is still widely used on many new and modern buildings around the world. With lead being so malleable, it is commonly specified and used for flashing, weathering and window hoods on roofs. It can easily be manipulated to fit various multi-curved contours and this can be done on site as required. Its grey-blue colour makes it ideal to blend in with concrete, brick and glass. Architects might specify the utilization of alloys of lead (e.g. antimony or antimony-arsenic) they may specify thinner gauges of sheet lead down to 3 lb. weight without reducing lead's normal advantages. Today, in addition to snow and ice and intense heat and cold, there are the corrosive elements of modern industrial atmospheres to combat (e.g. acid rain). Thus, lead is a natural material for atmospheric exposure due to its insolubility in sulfuric acid. The practice of using thinner gauge lead sheet for many applications increases the relevance of three basic rules to be followed if lead is to have the long service life that may be expected. These are:

• Individual pieces should be limited in size (the thinner the lead, the smaller each piece) so that the natural expansion and contraction is kept to a minimum, and the risk of severe distortion (with attendant danger of fatigue cracking) is thereby avoided.
• Fixings must not restrict thermal expansion and contraction, but must provide adequate long-term support to the lead.
• Joints must allow for thermal expansion and yet still be weather tight for the position in which they are used.