Replacing the Historic Roofing Material
Professional advice will be needed to assess the various aspects
of replacing a historic roof. With some exceptions, most historic
roofing materials are available today. If not, an architect or
preservation group who has previously worked with the same type
material may be able to recommend suppliers. Special roofing materials,
such as tile or embossed metal shingles, can be produced by manufacturers
of related products that are commonly used elsewhere, either on
the exterior or interior of a structure. With some creative thinking
and research, the historic materials usually can be found.
Determining the craft practices used in the installation of
a historic roof is another major concern in roof restoration.
Early builders took great pride in their work, and experience
has shown that the " rustic" or irregular designs
commercially labeled "Early American" are a 20thcentury
invention. For example, historically, wood shingles underwent
several distinct operations in their manufacture including splitting
by hand, and smoothing the surface with a draw knife. In modern
nomenclature, the same item would be a "tapersplit"
shingle which has been dressed. Unfortunately, the rustic appearance
of today's commercially available " handsplit" and
re-sawn shingle bears no resemblance to the handmade roofing
materials used on early American buildings.
Early craftsmen worked with a great deal of common sense; they
understood their materials. For example they knew that wood
shingles should be relatively narrow; shingles much wider than
about 6" would split when walked on, or they may curl or
crack from varying temperature and moisture. It is important
to understand these aspects of craftsmanship, remembering that
people wanted their roofs to be weathertight and to last a long
time. The recent use of "mothergoose" shingles
on historic structures is a gross underestimation of the early
Finding a modern craftsman to reproduce historic details may
take some effort. It may even involve some special instruction
to raise his understanding of certain historic craft practices.
At the same time, it may be pointless (and expensive) to follow
historic craft practices in any construction that will not be
visible on the finished product. But if the roofing details
are readily visible, their appearance should be based on architectural
evidence or on historic prototypes. For instance, the spacing
of the seams on a standingseam metal roof will affect the building's
overall scale and should therefore match the original dimensions
of the seams.
Many older roofing practices are no longer performed because
of modern improvements. Research and review of specific detailing
in the roof with the contractor before beginning the project
is highly recommended. For example, one early craft practice
was to finish the ridge of a wood shingle roof with a roof "comb"
that is, the top course of one slope of the roof was
extended uniformly beyond the peak to shield the ridge, and
to provide some weather protection for the raw horizontal edges
of the shingles on the other slope. If the "comb"
is known to have been the correct detail, it should be used.
Though this method leaves the top course vulnerable to the weather,
a disguised strip of flashing will strengthen this weak point.
Detail drawings or a sample mockup will help ensure
that the contractor or craftsman understands the scope and special
requirements of the project. It should never be assumed that
the modern carpenter, slater, sheet metal worker, or roofer
will know all the historic details. Supervision is as important
as any other stage of the process.