Understanding potential weaknesses of roofing material also requires
knowledge of repair difficulties. Individual slates can be replaced
normally without major disruption to the rest of the roof, but
replacing flashing on a slate roof can require substantial removal
of surrounding slates. If it is the substrate or a support material
that has deteriorated, many surface materials such as slate or
tile can be reused if handled care fully during the repair. Such
problems should be evaluated at the outset of any project to determine
if the roof can be effectively patched, or if it should be completely
replaced.
Will the repairs be effective? Maintenance costs tend to multiply
once trouble starts. As the cost of labor escalates, repeated
repairs could soon equal the cost of a new roof.
The more durable the surface is initially, the easier it will
be to maintain. Some roofing materials such as slate are expensive
to install, but if top quality slate and flashing are used, it
will last 40-60 years with minimal maintenance. Although the installation
cost of the roof will be high, low maintenance needs will make
the lifetime cost of the roof less expensive.
In a restoration project, research of documents and physical investigation
of the building usually will establish the roof's history. Documentary
research should include any original plans or building specifications,
early insurance surveys, newspaper descriptions, or the personal
papers and files of people who owned or were involved in the history
of the building. Old photographs of the building might provide
evidence of missing details.
Along with a thorough understanding of any written history of
the building, a physical investigation of the roofing and its
structure may reveal information about the roof's construction
history. Starting with an overall impression of the structure,
are there any changes in the roof slope, its configuration, or
roofing materials? Perhaps there are obvious patches or changes
in patterning of exterior brickwork where a gable roof was changed
to a gambrel, or where a whole upper story was added. Perhaps
there are obvious stylistic changes in the roof line, dormers,
or ornamentation. These observations could help one understand
any important alteration, and could help establish the direction
of further investigation.
Because most roofs are physically out of the range of careful
scrutiny, the "principle of least effort" has probably
limited the extent and quality of previous patching or replacing,
and usually considerable evidence of an earlier roof surface remains.
Sometimes the older roof will be found as an underlayment of the
current exposed roof. Original roofing may still be intact in
awkward places under later features on a roof. Often if there
is any unfinished attic space, remnants of roofing may have been
dropped and left when the roof was being built or repaired. If
the configuration of the roof has been changed, some of the original
material might still be in place under the existing roof. Sometimes
whole sections of the roof and roof framing will have been left
intact under the higher roof. The profile and/or flashing of the
earlier roof may be apparent on the interior of the walls at the
level of the alteration. If the sheathing or lathing appears to
have survived changes in the roofing surface, they may contain
evidence of the roofing systems. These may appear either as dirt
marks, which provide "shadows" of a roofing material,
or as nails broken or driven down into the wood,.rather than pulled
out during previous alterations or repairs. Wooden headers in
the roof framing may indicate that earlier chimneys or skylights
have been removed. Any metal ornamentation that might have existed
may be indicated by anchors or unusual markings along the ridge
or at other edges of the roof. This primary evidence is essential
for a full understanding of the roof's history.
"Roofing" an Historic Preservation Brief
