The Secretary of the Interior's "Standards for Rehabilitation"
call for the repair or replacement of missing architectural features
"based on accurate duplication of features, substantiated
by historic, physical, or pictorial evidence rather than on conjectural
designs." On a wooden shingle roof, it is important not only
to match the size, shape, texture, and configuration of historic
shingles, but also to match the craftsmanship and details that
characterize the historic roof. Proper installation and maintenance
will extend the life of the new roof.
Wooden shingle roofs are important elements of many historic buildings.
The special visual qualities imparted by both the historic shingles
and the installation patterns should be preserved when a wooden
shingle roof is replaced. This requires an understanding of the
size, shape, and detailing of the historic shingle and the method
of fabrication and installation. These combined to create roofs
expressive of particular architectural styles, which were often
influenced by regional craft practices. The use of wooden shingles
from the early settlement days to the present illustrates an extraordinary
range of styles.
Readily available and inexpensive sawn shingles were used not only for roofs, but for gables and wall surfaces. Photo: Lane County Historical Society.
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Wooden shingle roofs need periodic replacement. They can last
from 15 to over 60 years, but the shingles should be replaced
before there is deterioration of other wooden components of the
building. Appropriate replacement shingles are available, but
careful research, design, specifications, and the selection of
a skilled roofer are necessary to assure a job that will both
preserve the appearance of the historic building and extend the
useful life of the replacement roof.
Unfortunately, the wrong shingles are often selected or are installed
in a manner incompatible with the appearance of the historic roof.
There are a number of reasons why the wrong shingles are selected
for replacement roofs. They include the failure to identify the
appearance of the original shingles; unfamiliarity with available
products; an inadequate budget, or a confusion in terminology.
In any discussion about historic roofing materials and practices,
it is important to understand the historic definitions of terms
like "shingles," as well as the modern definitions or
use of those terms by craftsmen and the industry. Historically,
from the first buildings in America, these wooden roofing products
were called shingles, regardless of whether they were the earliest
handsplit or the later machine-sawn type. The term shake is a relatively
recent one and today is used by the industry to distinguish the
sawn products from the split products, but through most of our
building history there has been no such distinction.
Considering the confusion among architects and others regarding
these terms as they relate to the appearance of early roofs, it
should be stated that there is a considerable body of documentary
information about historic roofing practices and materials in
this country, and that many actual specimens of historic shingles
from various periods and places have been collected and preserved
so that their historic appearances are well established. Essentially,
the rustic looking shake that we see used so much today has little
in common with the shingles that were used on most of our early
buildings in America.
Throughout this Brief, the term shingle will be used to refer
to historic wooden roofs in general, whether split or sawn, and
the term shake will be used only when it refers to a commercially
available product. The variety and complexity of terminology used
for currently available products will be seen in the accompanying
chart entitled "Shingles and Shakes."
This Brief discusses what to look for in historic wooden shingle
roofs and when to replace them. It discusses ways to select or
modify modern products to duplicate the appearance of a historic
roof, offers guidance on proper installation, and provides information
on coatings and maintenance procedures to help preserve the new
roof.(1)
Because trees were plentiful from the earliest settlement days,
the use of wood for all aspects of construction is not surprising.
Wooden shingles were lightweight, made with simple tools, and
easily installed. Wooden shingle roofs were prevalent in the Colonies,
while in Europe at the same time, thatch, slate and tile were
the prevalent roofing materials.
With the popularity of the revival of historic styles in the late 19th and early 20th centuries, a new technique was developed to imitate English thatch roofs. Photo: C.H. Roofing.
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Distinctive roofing patterns
exist in various regions of the country that were settled by the
English, Dutch, Germans, and Scandinavians. These patterns and
features include the size, shape and exposure length of shingles,
special treatments such as swept valleys, combed ridges, and decorative
butt end or long side-lapped beveled handsplit shingles. Such features
impart a special character to each building, and prior to any
restoration or rehabilitation project the physical and photographic
evidence should be carefully researched in order to document the
historic building as much as possible. Care should be taken not
to assume that aged or deteriorated shingles in photographs represent
the historic appearance.
Shingle Fabrication. Historically wooden shingles were usually
thin (3/8"3/4"), relatively narrow (3"8"),
of varying length (14"36"), and almost always smooth.
The traditional method for making wooden shingles in the 17th
and 18th centuries was to handsplit them from log sections known
as bolts. These bolts were quartered or split
into wedges. A mallet and froe (or ax) were used to split or rive
out thin planks of wood along the grain. If a tapered shingle
was desired, the bolt was flipped after each successive strike
with the froe and mallet. The wood species varied according to
available local woods, but only the heartwood, or inner section,
of the log was usually used. The softer sapwood generally was
not used because it deteriorated quickly. Because handsplit shingles
were somewhat irregular along the split surface, it was necessary
to dress or plane the shingles on a shavinghorse with a draw-knife
or draw-shave to make them fit evenly on the roof.
This reworking was necessary to provide a tight-fitting roof over
typically open shingle lath or sheathing boards. Dressing, or
smoothing of shingles, was almost universal, no matter what wood
was used or in what part of the country the building was located,
except in those cases where a temporary or very utilitarian roof
was needed.
Shingle fabrication was revolutionized in the early 19th century
by steam-powered saw mills. Shingle mills made possible
the production of uniform shingles in mass quantities. The sawn
shingle of uniform taper and smooth surface eliminated the need
to hand dress. The supply of wooden shingles was therefore no
longer limited by local factors. These changes coincided with
(and in turn increased) the popularity of architectural styles
such as Carpenter Gothic and Queen Anne that used shingles to
great effect.
Handsplit shingles continued to be used in many places well after
the introduction of machine sawn shingles. There were, of course,
other popular roofing materials, and some regions rich in slate
had fewer examples of wooden shingle roofs. Some western "boom"
towns used sheet metal because it was light and easily shipped.
Slate, terneplate, and clay tile were used on ornate buildings
and in cities that limited the use of flammable wooden shingles.
Wooden shingles, however, were never abandoned. Even in the 20th
century, architectural styles such as the Colonial Revival and
Tudor Revival, used wooden shingles.
Modern wooden shingles, both sawn and split, continue to be made,
but it is important to understand how these new products differ
from the historic ones and to know how they can be modified for
use on historic buildings. Modern commercially available shakes
are generally thicker than the historic handsplit counterpart
and are usually left "undressed" with a rough, corrugated
surface. The rough surface shake, furthermore, is often promoted
as suitable for historic preservation projects because of its
rustic appearance. It is an erroneous assumption that the more
irregular the shingle, the more authentic or "historic"
it will appear.
Historic Detailing and Installation Techniques. While the size,
shape and finish of the shingle determine the roof's texture and
scale, the installation patterns and details give the roof its
unique character. Many details reflect the craft practices of
the builders and the architectural style prevalent at the time
of construction. Other details had specific purposes for reducing
moisture penetration to the structure. In addition to the most
visible aspects of a shingle roof, the details at the rake boards,
eaves, ridges, hips, dormers, cupolas, gables, and chimneys should
not be overlooked.
The long, biaxially tapered handsplit shingles are overlapped both vertically and horizontally. Photo: NPS files. |
The way the shingles were laid was often based on functional and
practical needs. Because a roof is the most vulnerable element
of a building, many of the roofing details that have become distinctive
features were first developed simply to keep water out. Roof combs
on the windward side of a roof protect the ridge line. Wedges,
or cant strips, at dormer cheeks roll the water away from the
vertical wall. Swept valleys and fanned hips keep the grain of
the wood in the shingle parallel to the angle of the building
joint to aid water runoff. The slight projection of the shingles
at the eaves directs the water runoff either into a gutter or
off the roof away from the exterior wall. These details varied
from region to region and from style to style. They can be duplicated
even with the added protection of modern flashing.
In order to have a weathertight roof, it was important to have
adequate coverage, proper spacing of shingles, and straight grain
shingles. Many roofs were laid on open shingle lath or open sheathing
boards. Roofers typically laid three layers of
shingles with approximately 1/3 of each shingle exposed to the
weather. Spaces between shingles (1/8"1/2" depending
on wood type) allowed the shingles to expand when wet. It was
important to stagger each overlapping shingle by a minimum of
11/2" to avoid a direct path for moisture to penetrate a
joint. Doubling or tripling the starter course at the eave gave
added protection to this exposed surface. In order for the roof
to lay as flat as possible, the thickness, taper and surface of
the shingles was relatively uniform; any unevenness on handsplit
shingles had already been smoothed away with a draw-knife. To keep
shingles from curling or cupping, the shingle width was generally
limited to less than 10".
Not all shingles were laid in evenly spaced, overlapping, horizontal
rows. In various regions of the country, there were distinct installation
patterns; for example, the biaxially-tapered long shingles occasionally
found in areas settled by the Germans. These long
shingles were overlapped on the side as well as on top. This formed
a ventilation channel under the shingles that aided drying. Because
ventilation of the shingles can prolong their life, roofers paid
attention to these details.
Early roofers believed that applied coatings would protect the
wood and prolong the life of the roof. In many cases they did;
but in many cases, the shingles were left to weather naturally
and they, too, had a long life. Eighteenth-century coatings included
a pine pitch coating not unlike turpentine, and boiled linseed
oil or fish oil mixed with oxides, red lead, brick dust, or other
minerals to produce colors such as yellow, Venetian red, Spanish
brown, and slate grey. In the 19th century, in addition to the
earlier colors, shingles were stained or painted to complement
the building colors: Indian red, chocolate brown, or brown-green.
During the Greek Revival and later in the 20th century with other
revival styles, green was also used. Untreated shingles age to
a silver-grey or soft brown depending on the wood species.
The craft traditions of the builders often played an important
role in the final appearance of the building. These elements,
different on each building, should be preserved in a re-roofing
project.
Historic wooden roofs using straight edge-grain heartwood shingles
have been known to last over sixty years. Fifteen to thirty years,
however, is a more realistic lifespan for most premium modern
wooden shingle roofs.
These weathered historic 19th-century handsplit and dressed shingles were found in place under a later altered roof. See also, below. Photo: John Ingle.
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Contributing factors to deterioration include
the thinness of the shingle, the durability of the wood species
used, the exposure to the sun, the slope of the roof, the presence
of lichens or moss growing on the shingle, poor ventilation levels
under the shingle or in the roof, the presence of overhanging
tree limbs, pollutants in the air, the original installation method,
and the history of the roof maintenance. Erosion of the softer
wood within the growth rings is caused by rainwater, wind, grit,
fungus and the breakdown of cells by ultraviolet rays in sunlight.
If the shingles cannot adequately dry between rains, if moss and
lichens are allowed to grow, or if debris is not removed from
the roof, moisture will be held in the wood and accelerate deterioration.
Moisture trapped under the shingle, condensation, or poorly ventilated
attics will also accelerate deterioration.
In addition to the eventual deterioration of wooden shingles,
impact from falling branches and workmen walking on the roof can
cause localized damage. If, however, over 20% of the shingles
on any one surface appear eroded, cracked, cupped or split, or
if there is evidence of pervasive moisture damage in the attic,
replacement should be considered. If only a few shingles are missing
or damaged, selective replacement may be possible. For limited
replacement, the old shingle is removed and a new shingle can
be inserted and held in place with a thin metal tab, or "babbie."
This reduces disturbance to the sound shingles above. In instances
where a few shingles have been cracked or the joint of overlapping
shingles is aligned and thus forms a passage for water penetration,
a metal flashing piece slipped under the shingle can stop moisture
temporarily. If moisture is getting into the attic, repairs must
be made quickly to prevent deterioration of the roof structural
framing members.
When damage is extensive, replacement of the shingles will be
necessary, but the historic sheathing or shingle lath under the
shingles may be in satisfactory condition. Often, the historic
sheathing or shingle laths, by their size, placement, location
of early nail holes, and water stain marks, can give important
information regarding the early shingles used. Before specifying
a replacement roof, it is important to establish the original
shingle material, configuration, detailing and installation. If the historic shingles are still in place, it is
best to remove several to determine the size, shape, exposure
length, and special features from the unweathered portions. If
there are already replacement shingles on the roof, it may be
necessary to verify through photographic or other research whether
the shingles currently on the roof were an accurate replacement
of the historic shingles.
The replacement shingles matched the historic shingles and were of such high quality that little hand dressing was needed at the site. Photo: John Ingle.
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The following information is needed in order to develop accurate
specifications for a replacement shingle:
Original wood type (White Oak, Cypress, Eastern White Pine, Western,
Red Cedar, etc.)
Size of shingle (length, width, butt thickness, taper)
Exposure length and nailing pattern (amount of exposure, placement
and type of nails)
Type of fabrication (sawn, handsplit, dressed, beveled, etc.)
Distinctive details (hips, ridges, valleys, dormers, etc.)
Decorative elements (trimmed butts, variety of pattern, applied
color coatings, exposed nails)
Type of substrate (open shingle lath or sheathing, closed sheathing,
insulated attics, sleepers, etc.)
Replacement roofs must comply with local codes which may require,
for example, the use of shingles treated with chemicals or pressure-impregnated
salts to retard fire. These requirements can usually be met without
long-term visual effects on the appearance of the replacement roof.
The accurate duplication of a wooden shingle roof will help ensure
the preservation of the building's architectural integrity. Unfortunately,
the choice of an inappropriate shingle or poor installation can
severely detract from the building's historic appearance. There are a number of commercially available wooden
roofing products as well as custom roofers who can supply specially-made
shingles for historic preservation projects. Unless restoration or reconstruction is being
undertaken, shingles that match the visual appearance of the historic
roof without replicating every aspect of the original shingles
will normally suffice. For example, if the historic wood species
is no longer readily available, Western Red Cedar or Eastern White
Pine may be acceptable. Or, if the shingles are located high on
a roof, sawn shingles or commercially available shakes with the
rustic faces factory-sawn off may adequately reproduce the appearance
of an historic handsplit and dressed shingle.
There will always be certain features, however, that are so critical
to the building's character that they should be accurately reproduced.
Following is guidance on matching the most important visual elements.
Highest Priority in Replacement Shingles:
* best quality wood with a similar surface texture
* matching size and shape: thickness, width, length
* matching installation pattern: exposure length, overlap, hips,
ridges, valleys, etc.
* matching decorative features: fancy butts, color, exposed nails
Areas of Acceptable Differences:
* species of wood
* method of fabrication of shingle, if visual appearance matches
* use of fire retardants, or preservative treatments, if visual
impact is minimal
* use of modern flashing, if sensitively installed
* use of small sleepers for ventilation, if the visual impact
is minimal and rake boards are sensitively treated
* method of nailing, if the visual pattern matches
Treatments and Materials to Avoid:
* highly textured wood surfaces and irregular butt ends, unless
documented
* standardized details (prefab hips, ridges, panels, etc.) unless
documented
* too wide shingles or those with flat grain (which may curl),
unless documented
What is Currently Available
Types of Wood: Western Red Cedar, Eastern White Pine, and White
Oak are most readily available today. For custom orders, cypress,
red oak, and a number of other historically used woods may still
be available. Some experiments using nontraditional woods (such
as yellow pine and hemlock) treated with preservative chemicals
are being tested for the new construction market, but are generally
too thick, curl too easily, or have too pronounced a grain for
use on historic buildings.
Method of manufacture: Commercially available modern shingles
and shakes are for the most part machine-made. While commercially
available shakes are promoted by the industry as handsplit, most
are split by machine (this reduces the high cost of hand labor).
True handsplit shingles, made the traditional way with a froe
and mallet, are substantially more expensive, but are more authentic
in appearance than the rough, highly textured machine-split shakes.
An experienced shingler can control the thickness of the handsplit
shingle and keep the shingle surface grain relatively even. To
have an even roof installation, it is important to have handsplit
shingles of uniform taper and to have less than 1/8th variation
across the surface of the shingle. For that reason, it is important
to dress the shingles or to specify uniform butt thickness, taper,
and surfaces. Commercially available shakes are shipped with a
range of butt sizes within a bundle (e.g., «", 5/8",
3/4" as a mix) unless otherwise specified. Commercially available
shakes with the irregular surfaces sawn off are also available.
In many cases, except for the residual circular saw marks, these
products appear not unlike a dressed handsplit shingle.
Sawn shingles are still made much the same way as they were historically--using
a circular saw. The circular saw marks are usually evident on
the surface of most sawn shingles. There are a number of grooved,
striated, or steamed shingles of the type used in the 20th century
to effect a rustic or thatched appearance. Custom sawn shingles
with fancy butts or of a specified thickness are still available
through mill shops. In fact, shingles can be fabricated to the
weathered thickness in order to be integrated into an existing
historic roof. If sawn shingles are being used as a substitute
for dressed handsplit shingles, it may be desirable to belt sand
the surface of the sawn shingles to reduce the prominence of the
circular saw marks.
As seen from the Shingle and Shake chart, few of the commercially
available shakes can be used without some modification or careful
specification. Some, such as heavy shakes with a corrugated face,
should be avoided altogether. While length, width, and butt configuration
can be specified, it is more difficult to ensure that the thickness
and the texture will be correct. For that reason, whatever shingle
or shake is desired, it is important to view samples, preferably
an entire bundle, before specifying or ordering. If shingles are
to be trimmed at the site for special conditions, such as fanned
hips or swept valleys, additional shingles should be ordered.
Coatings and Treatments: Shingles are treated to obtain a fire-retardant
rating; to add a fungicide preservative (generally toxic); to
revitalize the wood with a penetrating stain (oil as well as water based);
and to give color.
While shingles can be left untreated, local codes may require
that only fire-retardant shingles be used. In those circumstances,
there are several methods of obtaining rated shingles (generally
class "B" or "C"). The most effective and
longest lasting treatment is to have treated salts pressure-impregnated
into the wood cells after the shingles have been cut. Another
method (which must be periodically renewed) is to apply chemicals
to the surface of the shingles. If treated shingles need trimming
at the site, it is important to check with the manufacturer to
ensure that the fire-retardant qualities will not be lost. Pressure-impregnated
shingles, however, may usually be trimmed without loss of fire-retardant
properties.
The life of a shingle roof can be drastically shortened if moss,
lichens, fungi or bacterial spores grow on the wood. Fungicides
(such as chromated copper arsenate, CCA) have been found to be
effective in inhibiting such fungal growth, but most are toxic.
Red cedar has a natural fungicide in the wood cells and unless
the shingles are used in unusually warm, moist environments, or
where certain strains of spores are found, an applied fungicide
is usually not needed. For most woods, the Forest Products Laboratory
of the U.S. Department of Agriculture has found that fungicides
do extend the life of the shingles by inhibiting growth on or
in the wood. There are a variety available. Care should be taken
in applying these chemicals and meeting local code requirements
for proper handling.
Penetrating stains and water repellent sealers are sometimes recommended
to revitalize wood shingles subject to damage by ultraviolet rays.
Some treatments are oil-borne, some are waterborne, and some are
combined with a fungicide or a water repellent. If any of these
treatments is to be used, they should be identified as part of
the specifications. Manufacturers should be consulted regarding
the toxicity or other potential complications arising from the
use of a product or of several in combination. It is also important
not to coat the shingles with vapor impermeable solutions that
will trap moisture within the shingle and cause rotting from beneath.
New rounded butt sawn shingles, with a smooth finish and red oxide stain, were used to replace the deteriorated shingles. The varying widths, between 4" and 7" will keep them from curling and cupping. Exposure length was determined from historic nail patterns on the historic spaced sheathing below. Photo: NPS files.
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Specifications and roofing details should be developed for each
project. Standard specifications may be used as a basic format,
but they should be modified to reflect the conditions of each
job. Custom shingles can still be ordered that accurately replicate
a historic roof, and if the roof is simple, an experienced shingler
could install it without complicated instructions. Most rehabilitation
projects will involve competitive bidding, and each contractor
should be given very specific information as to what type of shingles
are required and what the installation details should be. For
that reason, both written specifications and detailed drawings
should be part of the construction documents.
For particularly complex jobs, it may be appropriate to indicate
that only roofing contractors with experience in historic preservation
projects be considered. By prequalifying the bidders,
there is greater assurance that a proper job will be done. For
smaller jobs, it is always recommended that the owner or architect
find a roofing contractor who has recently completed a similar
project and that the roofers are similarly experienced.
Specifications identify exactly what is to be received from the
supplier, including the wooden shingles, nails, flashing, and
applied coatings. The specifications also include instructions
on removing the old roofing (sometimes two or more earlier roofs),
and on preparing the surface for the new shingles, such as repairing
damage to the lath or sheathing boards. If there are to be modifications
to a standard product, such as cutting beveled butts, planing
off residual surface circular saw marks, or controlling the mixture
of acceptable widths (3"8"), these too should be specified.
Every instruction for modifying the shingles themselves should
be written into the specifications or they may be overlooked.
The specifications and drawn details should describe special features
important to the roof. Swept valleys, combed ridges, or wedged
dormer cheek runoffs should each be detailed not only with the
patterning of the shingles, but also with the placement of flashing
or other unseen reinforcements. There are some modern products
that appear to be useful. For example, paper coated and reinforced
metal laminated flashing is easy to use and, in combination with
other flashing, gives added protection over eaves and other vulnerable
areas; adhesives give a stronger attachment at projecting roofing
combs that could blow away in heavy wind storms. Clear or light colored
sealants may be less obvious than dark mastic often used in conjunction
with flashing or repairs. These modern treatments should not be
overlooked if they can prolong the life of the roof without changing
its appearance.
These commercially available roofing products with rustic split faces are not appropriate for historic preservation projects. Photo: NPS files.
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Certain common roofing practices for modern installations should
be avoided in re-roofing a historic building unless specifically
approved in advance by the architect. These practices interfere
with the proper drying of the shingles or result in a sloppy installation
that will accelerate deterioration. They include
improper coverage and spacing of shingles, use of staples to hold
shingles, inadequate ventilation, particularly for heavily insulated
attics, use of heavy building felts as an underlayment, improper
application of surface coatings causing stress in the wood surfaces,
and use of inferior flashing that will fail while the shingles
are still in good condition.
Avoid skimpy shingle coverage and heavy building papers. It has
become a common modern practice to lay impregnated roofing felts
under new wooden shingle roofs. The practice is especially prevalent
in roofs that do not achieve a full triple layering of shingles.
Historically, approximately one third of each single was exposed,
thus making a three-ply or three-layered roof. This assured adequate
coverage. Due to the expense of wooden shingles today, some roofers
expose more of the shingle if the pitch of the roof allows, and
compensate for less than three layers of shingles by using building
felts interwoven at the top of each row of shingles. This absorptive
material can hold moisture on the underside of the shingles and
accelerate deterioration. If a shingle roof has proper coverage
and proper flashing, such felts are unnecessary as a general rule.
However, the selective use of such felts or other reinforcements
at ridges, hips and valleys does appear to be beneficial.
Beware of heavily insulated attic rafters. Historically, the longest
lasting shingle roofs were generally the ones with the best roof
ventilation. Roofs with shingling set directly on solid sheathing
and where there is insulation packed tightly between the wooden
rafters without adequate ventilation run the risk of condensation-related
moisture damage to wooden roofing components. This is particularly
true for air-conditioned structures. For that reason, if insulation
must be used, it is best to provide ventilation channels between
the rafters and the roof decking, to avoid heavy felt building
papers, to consider the use of vapor barriers, and perhaps to
raise the shingles slightly by using "sleepers" over
the roof deck. This practice was popular in the 1920s in what
the industry called a "Hollywood" installation, and
examples of roofs lasting 60 years are partly due to this undershingle
ventilation.
Avoid staples and inferior flashing. The common practice of using
pneumatic staple guns to affix shingles can result in shooting
staples through the shingles, in crushing the wood fibers, or
in cracking the shingle. Instead, corrosion resistant nails, generally
with barked or deformed shanks long enough to extend about 3/4"
into the roof decking, should be specified. Many good roofers
have found that the pneumatic nail guns, fitted with the proper
nails and set at the correct pressure with the nails just at the
shingle surface, have worked well and reduced the stress on shingles
from missed hammer blows. If red cedar is used, copper nails should
not be specified because a chemical reaction between the wood
and the copper will reduce the life of the roof. Hot-dipped, zinc-coated,
aluminum, or stainless steel nails should be used. In addition,
copper flashing and gutters generally should not be used with
red cedar shingles as staining will occur, although there are
some historic examples where very heavy gauge copper was used
which outlasted the roof shingles. Heavier weight flashing (2()
oz.) holds up better than lighter flashing, which may deteriorate
faster than the shingles. Some metals may react with salts or
chemicals used to treat the shingles. This should be kept in mind
when writing specifications. Terne-coated stainless steel and lead-coated
copper are generally the top of the line if copper is not appropriate.
Avoid patching deteriorated roof lath or sheathing with plywood
or composite materials. Full size lumber may have to be custom ordered
to match the size and configuration of the original sheathing
in order to provide an even surface for the new shingles. It is
best to avoid plywood or other modern composition boards that
may deteriorate or delaminate in the future if there is undetected
moisture or leakage. If large quantities of shingle lath or sheathing
must be removed and replaced, the work should be done in sections
to avoid possible shifting or collapse of the roof structure.
Avoid spray painting raw shingles on a roof after installation.
Rapidly drying solvent in the paint will tend to warp the exposed
surface of the shingles. Instead, it is best to dip new shingles
prior to installation to keep all of the wood fibers in the same
tension. Once the entire shingle has been treated, however, later
coats can be limited to the exposed surface.
The purpose of regular or routine maintenance is to extend the
life of the roof. The roof must be kept clean and inspected for
damage both to the shingles and to the flashing, sheathing, and
gutters. If the roof is to be walked on, rubber soled shoes should
be worn. If there is a simple ridge, a ladder can be hooked over
the roof ridge to support and distribute the weight of the inspector.
Keeping the roof free of debris is important. This may involve
only sweeping off pine needles, leaves and branches as needed.
It may involve trimming overhanging branches. Other aspects of
maintenance, such as removal of moss and lichen buildup, are more
difficult. While they may impart a certain charm to roofs, these
moisture-trapping organisms will rot the shingles and shorten the
life of the roof. Buildups may need scraping and the residue removed
with diluted bleaching solutions (chlorine), although caution
should be used for surrounding materials and plants. Some roofers
recommend power washing the roofs periodically to remove the dead
wood cells and accumulated debris. While this makes the roof look
relatively new, it can put a lot of water under shingles, and
the high pressure may crack or otherwise damage them. The added
water may also leach out applied coatings.
If the roof has been treated with a fungicide, stain, or revitalizing
oil, it will need to be re-coated every few years (usually every
4-5). The manufacturer should be consulted as to the effective
life of the coating. With the expense associated with installation
of wood shingles, it is best to extend the life of the roof as
long as possible. One practical method is to order enough shingles
in the beginning to use for periodic repairs.
Periodic maintenance inspections of the roof may reveal loose
or damaged shingles that can be selectively replaced before serious
moisture damage occurs. Keeping the wooden shingles
in good condition and repairing the roof, flashing and guttering,
as needed, can add years of life to the roof.
A combination of careful research to determine the historic appearance
of the roof, good specifications, and installation details designed
to match the historic roof, and long-term maintenance, will make
it possible to have not only a historically authentic roof, but
a cost-effective one. It is important that professionals be part
of the team from the beginning. A preservation architect should
specify materials and construction techniques that will best preserve
the roof's historic appearance. The shingle supplier must ensure
that the best product is delivered and must stand behind the guarantee
if the shipment is not correct. The roofer must be knowledgeable
about traditional craft practices. Once the new shingle roof is
in place, it must be properly maintained to give years of service.
NOTE
(1) Preservation Brief 4: Roofing for Historic Buildings discusses
research methods, analysis of deterioration, and the general significance
of historic roofs.
Further Reading
Bucher, Robert C. "The Long Shingle." Pennsylvania Folklife,
Vol. XVIII, No. 4, Summer 1969.
Cox, Richard E. "Wooden Shingles from the Fortress of Louisbourg."
Bulletin of the Association for Preservation Technology, Vol.
Il, Nos. 12 1970 p.p.65.
Engle, Reed. "Restoring a Roofing." CRM Bulletin, a
publication of the National Park Service, Vol. 8, No. 6 Dec. 1985.
Kidder, F.E. Building Construction and Superintendence, Part II.
New York: William T. Comstock, 1902.
LeVan, Susan. "FireRetardant Treatments for Wood Shingles."
Techline, Madison, Wisconsin: U.S.D.A. Forest Service, 1988.
Niemiec, S.S. and T.D. Brown. "Care and Maintenance of Wood
Shingle and Shake Roofs. " Oregon State University Extension
Service, September 1988. Publication #EC 1271.
The Old House Journal, Vol. XI, No. 3, April 1983. Special Roof
Issue.
Peterson, Charles E. (editor). Building Early America. Radnor,
Pennsylvania: Chilton Book Co. 1976.
Stevens, John. "Shingles." Bulletin of the Association
for Preservation Technology, Vol. II, Nos. 12 1970, pp. 74.
Sweetser, Sarah M. Preservation Briefs 4: Roofing for Historic
Buildings. Washington, D.C.: Technical Preservation Services Division,
National Park Service, U.S. Department of the Interior, 1978.
Tollesten, Kristin. "Shingles and Shingled Roofs." No
Future Without the Past. Rome, Italy: ICOMOS, 1981. pp. 347360.
Acknowledgements
The author gratefully acknowledges the invaluable assistance of
co-worker Michael Auer in preparing this brief for publication.
In addition, the following individuals are to be thanked for their
contribution to this manuscript: Reed Engle, Historical Architect,
NPS; John Ingle, Historical Architect, NPS; Martin Obando, Eastern
District Manager, Red Cedar Shingle & Handsplit Shake Bureau;
and Peter Sandbeck, North Carolina Division of Archives and History.
Appreciation is extended to: the staff of Technical Preservation
Services Branch and NPS regional offices; Michael Lynch of the
Office of Parks, Recreation and Historic Preservation in Albany,
New York; and to Penelope H. Batcheler and William Brookover,
Historical Architects, Independence National Historic Park, for
their review of this manuscript and constructive comments. Special
thanks are given to Kaye Ellen Simonson for the illustrations
in the charts. Washington, D.C. September, 1989
Home page logo: Appropriate re-roofing work in progress. Photo: NPS files.
This publication has been prepared pursuant to the National
Historic Preservation Act of 1966, as amended, which directs the Secretary
of the Interior to develop and make available information concerning historic
properties. Technical Preservation Services (TPS), Heritage Preservation
Services Division, National Park Service prepares standards, guidelines,
and other educational materials on responsible historic preservation treatments
for a broad public.