For many years the architectural sheet metal craftsmen has faithfully followed the practices established from early designs of metal roofing. The standing seam, batten seam and flat seam have long been accepted and cherished standards for copper roofing.
Perhaps copper's most outstanding characteristics is its durability. This is especially important with roofs since they are required to protect the entire investment. Copper's time-proven record attests to its ability to withstand years - even centuries - of exposure to most atmospheres. No other roofing material commonly used in modern architecture can measure up to copper.
One of the oldest forms of copper roofing - standing seam - is as elegant, graceful and architecturally tasteful today as it was in 1787 when Christ Church in Philadelphia was first sheathed in copper. This installation served for over 150 years, when it became necessary to replace the wood decking, which meant replace of the copper, too. The copper was reported to be in "generally good" condition.
There is a chapel in England, built during the 8th century, which has one of the oldest slate roofs known. After 1,200 years of service, the moss-covered roof is still in good condition, demonstrating the permanence of the material. From 12th-century English Castles to the chateaux of Renaissance France, we can see samples of the lasting beauty of slate.
Slate is more than just insurance that a roof will outlive its builder. It has a natural, hand-processed quality and a variety of textures and colors that give it richness that no other roofing material can claim.
Geologically, slate is a metamorphic rock which began as a sediment deposited under a body of water and changed under tremendous heat and pressure into the fine-grained hard rock we know. Variations in local chemistry and the conditions under which it was formed have produced a wide range of colors and qualities.
The advantages of a slate roof are numerous. Compared with the common asphalt roof, which has a life expectancy of perhaps 20 years. The weight of slate depends on its size, thickness, and variety.
Slate will last a life time. Roofing slate begins at approximately 700 lbs. per 100 sq. ft., covering a roof while the difference seems unreasonable, remember that a cedar shake roof of approximately 450 lbs. will absorb three times its weight in water and hold a tremendous amount of snow. Slate, on the other hand, is almost nonabsorbent and sheds snow like a sliding board.
Installation techniques are much the same today as they were for centuries.
During the preparation of this, many requests to include in it a list of the advantages of slate in direct comparison with other roofing materials were received from architects, contractors, and especially from prospective home builders.
The policy of the National Slate Association is, and always has been, never to point out the faults or weaknesses of a competitive or a substitute material for any of the uses of slate. Such procedure conforms with sound business ethics, and, in line with this policy, the editors merely list in convenient form the outstanding characteristics which make slate such a valuable roofing material.