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 Sometimes, however, historic materials are not available, or the
skilled craftsmen needed to fabricate or install them can not be
found. Sometimes, the old materials do not work as well, do not
last as long, or cost more than modern substitutes. Under
certain circumstances the modern substitutes may be used instead
of the original materials to make repairs or replacements on
historic buildings. In addition to such tried-and-true choices
as wood, stamped metal, or mineral fiber cement shingles, modern
technology offers many less familiar materials that work well for
certain repair or replacement chores, especially if they are used
in places that are not seen up close. These substitutes look and
behave much like the originals and can be installed without
damaging historic features. They may or may not be competitively
priced.
Caution: The use of vinyl or aluminum siding and molded
urethanes as cosmetic claddings or substitutes for wooden
millwork should be avoided. Millwork is still readily available
and should always be replaced in-kind in exterior projects.
Carefully chosen substitute materials may be acceptable when:
o
The historic material is no longer available, or when it
cannot be delivered within a reasonable length of time.
o
There are no skilled craftsmen available to repair the
original feature in place or to install matching material.
o
The historic materials are of poor quality or are not
suitable for the use they were put to. Example: Early
sheet metal roofs were made of tinplate, which corroded
easily. The closest modern equivalent of tinplate is
terne-coated steel, but the steel may corrode if the terne
coating is scratched. A more durable (though more
expensive) choice for a replacement roof on a historic
building might be terne-coated stainless steel or
lead-coated copper because these materials wear much
better and look very much like the original tinplate.
o
Building or life-safety codes require the use of specific
modern materials or prohibit using the historic ones.
o
The cost of the original material is prohibitive.
Example: High-quality slate roofs can last sixty years or
more with minimal maintenance. They may actually be more
economical in the long run than other materials that cost
less initially but need more frequent maintenance and
replacement. However, if short-term cost has to be the
deciding factor in choosing a replacement roofing
material, a badly damaged or deteriorated slate roof might
be replaced with mineral fiber cement shingles, which look
very much like slate, cost considerably less, and can last
twenty to twenty-five years if properly installed and well
maintained.
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