The use of the historic roofing material on a structure may be
restricted by building codes or by the availability of
the materials, in which case an appropriate alternative will have
to be found.
Some municipal building codes allow variances for roofing materials
in historic districts. In other instances, individual variances
may be obtained. Most modern heating and cooking is fueled by
gas, electricity, or oil none of which emit the hot embers
that historically have been the cause of roof fires. Where wood
burning fireplaces or stoves are used, spark arrestor screens
at the top of the chimneys help to prevent flaming material from
escaping, thus reducing the number of fires that start at the
roof. In most states, insurance rates have been equalized to reflect
revised considerations for the risks involved with various roofing
In a rehabilitation project, there may be valid reasons for replacing
the roof with a material other than the original. The historic
roofing may no longer be available, or the cost of obtaining specially
fabricated materials may be prohibitive. Butthe decision to use
an alternative material should be weighed carefully against the
primary concern to keep the historic character of the building.
If the roof is flat and is not visible from any elevation of the
building, and if there are advantages to substituting a modern
builtup composition roof for what might have been a flat metal
roof, then it may make better economic and construction sense
to use a modern roofing method. But if the roof is readily visible,
the alternative material should match as closely as possible the
scale, texture, and coloration of the historic roofing material.
Asphalt shingles or ceramic tiles are common substitute materials
intended to duplicate the appearance of wood shingles,slates,
or tiles. Fire retardant, treated wood shingles are currently
available. The treated wood tends, however, to be brittle, and
may require extra care (and expense) to install. In some instances,
shingles laid with an interlay of fireretardant building paper
may be an acceptable alternative.
Lead-coated copper, ternecoated steel, and aluminum/ zinc-coated
steel can successfully replace tin, terne plate, zinc, or lead.
Copper-coated steel is a less expensive (and less durable)
substitute for sheet copper.
The search for alternative roofing materials is not new. As early
as the 18th century, fear of fire cause many wood shingle or board
roofs to be replaced by sheet metal or clay tile. Some historic
roofs were failures from the start, based on overambitious and
naive use of materials as they were first developed. Research
on a structure may reveal that an inadequately designed or a highly
combustible roof was replaced early in its history, and therefore
restoration of a later roof material would have a valid precedent.
In some cities, the substitution of sheet metal on early row houses
occurred as soon as the rolled material became available.
Cost and ease of maintenance may dictate the substitution of
a material wholly different in appearance from the original. The
practical problems (wind, weather, and roof pitch) should be weighed
against the historical consideration of scale, texture, and color.
Sometimes the effect of the alternative material will be minimal.
But on roofs with a high degree of visibility and patterning or
texture, the substitution may seriously alter the architectural
character of the building.