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The Repair and Replacement of
Historic Wooden Shingle Roofs
Sharon C. Park, AIA
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.
Introduction
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 (see illus.
1, 2, 3, 4).
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)
Wooden Shingle Roofs
in America
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. 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 (see illus. 5A). 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 (see illus. 5B) 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 (see illus. 6). 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 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 (see illus.
7). 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 (see illus. 8). 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
(see illus. 9).
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. The Historic Details and Installation
Patterns Chart (see illus. 10) identifies many of the features found
on historic wooden roofs. These elements, different on each building,
should be preserved in a re-roofing project.
Replacing Deteriorated Roofs: Matching the Historic Appearance
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. 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
(see illus. 11). 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 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 (see illus. 12). 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 (see Shingle and Shake Chart, illus. 13). 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.
Specifications
for the Replacement Roof
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 (see illus. 14). 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.
Roofing Practices to Avoid
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 (see illus. 15). 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 (refer to illus.
9).
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.
Maintenance
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 45).
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 (see illus. 16). Keeping the wooden shingles in good condition
and repairing the roof, flashing and guttering, as needed, can add years
of life to the roof.
Conclusion
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 coworker
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.
September, 1989
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