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The Preservation and Repair
of Historic Clay Tile Roofs
Anne E. Grimmer and Paul K. Williams
Clay tiles are one of the most distinctive and decorative historic
roofing materials because of their great variety of shapes, colors,
profiles, patterns, and textures. Traditionally, clay tiles were formed
by hand, and later by machine extrusion of natural clay, textured or
glazed with color, and fired in high-temperature kilns. The unique visual
qualities of a clay tile roof often make it a prominent feature in defining
the overall character of a historic building (Fig. 1). The significance
and inherently fragile nature of historic tile roofs dictate that special
care and precaution be taken to preserve and repair them.
Clay tile has one of the longest life expectancies among historic
roofing materials-generally about 100 years, and often several hundred.
Yet, a regularly scheduled maintenance program is necessary to prolong
the life of any roofing system. A complete internal and external inspection
of the roof structure and the roof covering is recommended to determine
condition, potential causes of failure, or source of leaks, and will
help in developing a program for the preservation and repair of the
tile roof. Before initiating any repair work on historic clay tile roofs,
it is important to identify those qualities important in contributing
to the historic significance and character of the building.
This Brief will review the history of clay roofing tiles and will
include a description of the many types and shapes of historic tiles,
as well as their different methods of attachment. It will conclude with
general guidance for the historic property owner or building manager
on how to plan and carry out a project involving the repair and selected
replacement of historic clay roofing tiles. Repair of historic clay
tile roofs is not a job for amateurs; it should be undertaken only by
professional roofers experienced in working with clay tile roofs.
Historical Background
The origin of clay roofing tile can be traced independently to two
different parts of the world: China, during the Neolithic Age, beginning
around 10,000 B.C.; and the Middle East, a short time later. From these
regions, the use of clay tile spread throughout Asia and Europe. Not
only the ancient Egyptians and Babylonians, but also the Greeks and
Romans roofed their buildings with clay tiles, and adaptations of their
practice continue in Europe to the present. European settlers brought
this roofing tradition to America where it was established in many places
by the 17th century.
Archeologists have recovered specimens of clay roofing tiles from
the 1585 settlement of Roanoke Island in North Carolina. Clay tile was
also used in the early English settlements in Jamestown, Virginia, and
nearby St. Mary's in Maryland. Clay roofing tiles were also used in
the Spanish settlement of St. Augustine in Florida, and by both the
French and Spanish in New Orleans.
Dutch settlers on the east coast first imported clay tiles from Holland.
By 1650, they had established t ~u ~ full-scale production of clay tiles
in the upper Hudson River Valley, shipping tiles south to New Amsterdam
(Fig. 2). Several tile manufacturing operations were in business around
the time of the American Revolution, offering both colored and glazed
tile and unglazed natural terra-cotta tile in the New York City area,
and in neighboring New Jersey. A 1774 New York newspaper advertised
the availability of locally produced, glazed and unglazed pantiles for
sale that were guaranteed to "stand any weather." On the west coast
clay tile was first manufactured in wooden molds in 1780 at Mission
San Antonio de Padua in California by Indian neophytes under the direction
of Spanish missionaries (Fig. 3).
By far the most significant factor in popularizing clay roofing tiles
during the Colonial period in America was the concern with fire. Devastating
fires in London, 1666, and Boston in 1679, prompted the establishment
of building and fire codes in New York and Boston. These fire codes,
which remained in effect for almost two centuries, encouraged the use
of tile for roofs, especially in urban areas, because of its fireproof
qualities. Clay roofing tile was also preferred because of its durability,
ease of maintenance, and lack of thermal conductivity.
Although more efficient production methods had lowered the cost of
clay tile, its use began to decline in much of the northeastern United
States during the second quarter of the 19th century. In most areas
outside city-designated fire districts, wood shingles were used widely;
they were more affordable and much lighter, and required less heavy
and less expensive roof framing. In addition, new fire-resistant materials
were becoming available that could be used for roofing, including slate,
and metals such as copper, iron, tin-plate, zinc, and galvanized iron.
Many of the metal roofing materials could be installed at a fraction
of the cost and weight of clay tile. Even the appearance of clay tile
was no longer fashionable, and by the 1830s clay roofing tiles had slipped
temporarily out of popularity in many parts of the country.
Revival Styles Renew Interest in Clay Roofing Tiles
By the mid-19th century, the introduction of the Italianate Villa
style of architecture in the United States prompted a new interest in
clay tiles for roofing. This had the effect of revitalizing the clay
tile manufacturing industry, and by the 1870s, new factories were in
business, including large operations in Akron, Ohio, and Baltimore,
Maryland. Clay tiles were promoted by the Centennial Exhibition in Philadelphia
in 1876, which featured several prominent buildings with tile roofs,
including a pavilion for the state of New Jersey roofed with clay tiles
of local manufacture. Tile-making machines were first patented in the
1870s, and although much roofing tile continued to be made by hand,
by the 1880s more and more factories were beginning to use machines
(Fig. 4). The development of the Romanesque Revival style of architecture
in the 1890s further strengthened the role of clay roofing tiles as
an American building material (Fig. 5).
Alternative substitutes for clay tiles were also needed to meet this
new demand. By about 1855, sheet metal roofs designed to replicate the
patterns of clay tile were being produced. Usually painted a natural
terra cotta color to emulate real clay tile, these sheet metal roofs
became popular because they were cheaper and lighter, and easier to
install than clay tile roofs.
Clay roofing tiles fell out of fashion again for a short time at the
end of the 19th century, but once more gained acceptance in the 20th
century, due primarily to the popularity of the Romantic Revival architectural
styles, including Mission, Spanish, Mediterranean, Georgian and Renaissance
Revival in which clay tile roofs featured prominently. With the availability
of machines capable of extruding clay in a variety of forms in large
quantities, clay tiles became more readily available across the nation.
More regional manufacturing plants were established in areas with large
natural deposits of clay, including Alfred, New York; New Lexington,
Ohio; Lincoln, California; and Atlanta, Georgia; as well as Indiana,
Illinois and Kansas.
The popularity of clay tile roofing, and look-alike substitute roofing
materials, continues in the 20th century, especially in areas of the
South and West-most notably Florida and California-where Mediterranean
and Spanish-influenced styles of architecture still predominate (Fig.
6).
Early Tiles
During the 17th and 18th centuries the most common type of clay roofing
tiles used in America were flat and rectangular. They measured approximately
10" x 6" x ‡" (25cm x 15cm x 1.25cm), and had two nail or peg
holes at one end through which they were anchored to the roofing laths.
Sometimes a strip of mortar was placed between the overlapping rows
of tile to prevent the tiles from lifting in high winds. In addition
to flat tiles, interlocking S-shaped pantiles were also used in the
18th century. These were formed by molding clay over tapered sections
of logs, and were generally quite large. Alternately termed pan, crooked,
or Flemish tiles, and measuring approximately 14 ‡" x 9 ‡"
(37cm x 24cm), these interlocking tiles were hung on roofing lath by
means of a ridge or lug located on the upper part of the underside of
each tile. Both plain (flat) tile and pantile (S-shaped or curved) roofs
were capped at the ridge with semicircular ridge tiles. Clay roofing
tiles on buildings in mid-18th century Moravian settlements in Pennsylvania
closely resembled those used in Germany at the time. These tiles were
about 14"15" long x 6"7" wide (36cm-38cm x 15cm-18cm) with a curved
butt, and with vertical grooves to help drainage. They were also designed
with a lug or nib on the back so that the tiles could hang on lath without
nails or pegs.
The accurate dating of early roofing tiles is difficult and often
impossible. Fragments of tile found at archeological sites may indicate
the existence of clay tile roofs, but the same type of tile was also
sometimes used for other purposes such as paving, and in bake ovens.
To further complicate dating, since clay tile frequently outlasted many
of the earliest, less permanent structures, it was often reused on later
buildings.
Clay Tile Substitutes
In addition to sheet metal "tile" roofs introduced in the middle of
the 19th century, concrete roofing tile was developed as another substitute
for clay tile in the latter part of the 19th century (Fig. 7). It became
quite popular by the beginning of the 20th century. Concrete tile is
composed of a dense mixture of portland cement blended with aggregates,
including sand, and pigment, and extruded from high-pressure machines.
Although it tends to lack the color permanence and the subtle color
variations inherent in natural clay tile, concrete tile continues to
be a popular roofing material today because it reproduces the general
look of clay tile, if not always the exact profile or proportions of
historic clay tile, at a somewhat lower cost and weight. Another modern,
slightly cheaper and lighter substitute for clay tile more recently
developed consists of a mixture of mineral fiber and cement with pigments
added to supply color. While these aggregate tiles also replicate the
shape and appearance of clay roofing tiles, they have many of the same
dissimilarities to clay tiles that are found in concrete tiles. Thus,
like concrete tiles, they are seldom appropriate substitutes for clay
tiles.
Traditional
Tile Shapes and Colors
There are two types of clay roofing tiles: interlocking and overlapping.
Interlocking tiles are designed in pairs so that an extrusion or "lip"
on one of the tiles "hooks" over the other tile thereby "locking" or
securing the two together; they are also usually nailed to the roof
structure. Overlapping tiles, which can also function in pairs, generally
do not have any sort of "lip" and must be nailed in place. There is
a wide range of shapes of historic clay roofing tiles, and many, sometimes
with slight variations, are still produced today. There are many variations,
and the country of origin of some of them may be revealed in their names,
but there are essentially only two kinds of shapes: pantiles and flat
tiles. Both pantiles and flat tiles may be either interlocking or overlapping
(Figs. 89).
Pantiles. The shape most commonly associated with historic clay roofing
tiles is probably that of convex or rounded tiles, often grouped together
generically as "pan tiles" or "pantiles." These include Spanish tiles-sometimes
called "S" tiles, or the similarly shaped Mission tiles, also known
as Barrel or Barrel Mission tiles, straight or tapered, as well as Roman
tiles, and their Greek variation.
Flat Tiles. Flat, shingle tiles are another type of historic clay
roofing tiles. Flat tiles can be completely plain and flat, and, like
roofing slates, overlap one another, attached with nails to the roof
sheathing. Or they may interlock at the top and on one side. Although
the "interlock" holds them together, most interlocking shingle tiles
also have one or more holes, usually near the top, for nailing to the
roof sheathing. Flat tiles are mostly variations of English or Shingle
tiles, and include English Shingle, Closed Shingle, Flat, Shingle or
Slab Shingle, as well as French tiles which have a slightly higher and
more contoured profile.
Any of the standard tile shapes may be known by a different name in
another region of the country, or in different parts of the world. For
example, what are known as Spanish or "S" tiles in the United States,
may be called Single Roman tiles in England. Sometimes Spanish and Mission
tiles are equated despite the fact that the former are usually 1-piece
interlocking tiles and the latter are single ‡ cylinders that
overlap. Since missions and the Mission style are associated with the
Americas, Mission tiles in the United States are more commonly referred
to as Spanish tiles in England and Europe. In a similar vein, Spanish
or "S" tiles, or Barrel tiles, might seem to be more typical of some
tiles used in France than what are marketed as French tiles by American
manufacturers.
Today some tile manufacturers have given their own trademark name
to historic tile shapes. Other companies market uniquely shaped "S"
tiles that are more in the shape of a true, but rather low profile "s"
without the customary flat portion of traditional American "S" tiles.
Field and Specialty Tile. The tiles that cover the majority of the
flat surface of the roof are called field tile. Some roof shapes, particularly
conical towers or turrets, require tiles of graduated sizes, and some
shapes or patterns of field tile also require specially shaped finish
tiles to complete the roof covering package. Other uniquely-shaped tiles
were made to fit odd-shaped spaces and places including dormers and
valleys, roof hips, rakes, ridges and corners. There are also finish
tiles that fulfill certain needs, such as eave closures or clay plugs
called "birdstops." These are intended to keep out snow and rain, and
birds from nesting in the voids under the bottom row of curved tiles.
Different patterns and designs can also be created by combining, or
mixing and matching flat tiles with dimensional tiles.
Tile Colors. A terra cotta red is the color most commonly associated
with historic clay roofing tiles. The reddish color comes from clay
with a large percentage of iron oxide, and there are many variations
of this natural color to be found in tiles ranging from deep reddish
browns to softer and paler oranges and pinks. Lighter buff and beige
colors, as well as black, also appear on traditional tile-roofed buildings.
Buff-colored tiles were made from nearly pure fire clay, and pouring
manganese dissolved in water over the tile before firing resulted in
smoke brown or black glazed tiles. Toward the end of the 19th century
the popularity of colored glazes for roofing tiles increased, and their
use and the range of colors continues to expand today. Most historic
glazed roofing tiles are in fairly natural hues that range from reds
and browns and buffs, to blacks and purples, blues (often created with
smalt, or powdered blue glass), and a wide variety of greens (usually
created with copper slag). There could be a considerable range in the
colors of tiles that were baked over a wood fire because the temperature
within the kiln was so uneven; tiles closest to the fire cooked all
the way through and turned a darker red, while tiles farthest from the
flames were likely to be smoke-stained, and lighter orange in color.
How Tiles are Attached
The method used to attach clay roofing tiles varies according to the
shape, size and style of the particular tile. For the most part, traditional
and modern methods of installing clay roofing tiles are very similar,
except that modern practice always includes the use of wood sheathing
and roofing felt. But most of the earliest clay roofing tiles were laid
without benefit of wood sheathing and hung directly on roofing laths
and battens that were nailed to the roof rafters; this practice continued
up into the mid-19th century in some regions. While this method of attachment
allowed for plenty of ventilation, and made it easy to find leaks and
make repairs, it also meant that the overall water-tightness of the
roof depended entirely on the tiles themselves.
Gradually, the practice evolved of nailing roofing tiles directly
onto continuous wood sheathing, or hanging them from "nibs" on horizontal
lath that was attached to roof rafters or sheathing. Some kinds of tile,
especially the later Mission or Barrel tiles were laid over vertical
strips or battens nailed to the sheathing, or the tiles were fastened
to wood purlins with copper wire.
Partly because they do not always fit together very closely, some
tile shapes, including Spanish, Barrel or Mission as well as other types
of interlocking tiles, are not themselves completely water-repellent
when used on very low-pitched roofs. These have always required some
form of sub-roofing, or an additional waterproof underlayer, such as
felting, a bituminous or a cementitious coating. In some traditional
English applications, a treatment called "torching," involved using
a simple kind of mortar most commonly consisting of
straw, mud, and moss. The tapered Mission tiles of the old Spanish
missions in California were also laid in a bed of mud mortar mixed with
grass or straw which was their only means of attachment to the very
low-pitched reed or twig sheathing (latia) that supported the
tiles (Fig. 10).
More recent and contemporary roofing practices require that the tiles
be laid on solid l" (2.5cm) wood sheathing felted with coated base sheets
of at least 30 lbs., or built-up membranes or single-ply roof membranes.
This substantially increases the water-tightness of the roof by adding
a second layer of waterproofing. Horizontal and vertical chalk lines
are drawn to serve as a guide in laying the tile and to indicate its
patterning. Most tiles are designed with one or two holes so they can
be attached by copper nails or hangers, and/or with projecting nibs,
to interlock or hang on battens or lath attached to the base sheathing.
Before laying the tiles, the copper or lead gutters, flashings and
valleys must be installed, preferably using at least #26 gauge (2024
ounce) corrosion-resistant metal extending a minimum of 12" (30.5cm)
under the tile from the edge, or in accordance with the manufacturer's
specifications. The long life and expected durability of clay tiles
require that, as with the roofing nails, only the best quality metal
be selected for the flashing and guttering.
"Field tile" is usually ordered by the number of "squares"-that is,
a flat section 10" x 10" (25cm x 25cm)--needed to cover a roof section.
The tile company or roofing contractor should calculate the number of
tiles needed according to the type of roof, and based on architect's
drawings to ensure accuracy. This should include specialty ridge and
eave tiles, decorative trim, partial "squares" approximately 1020 per
cent allowance for breakage, and extra tiles to store for repairing
incidental damage later on. Once at the site, the tile is evenly distributed
in piles on the roof, within easy reach for the roofers.
The tiles are laid beginning with the first course at the lower edge
of the roof at the eaves. The method by which roofing tiles are laid
and attached varies, depending on the type and design of the tiles and
roof shape, as well as on regional practice and local weather conditions.
A raised fascia, a cant strip, a double or triple layer of tiles, or
special "birdstop" tiles for under the eaves, may be used to raise the
first row of tiles to the requisite height and angle necessary for the
best functioning of the roof (Fig. 11). The tile is positioned to overhang
the previously installed gutter system by at least 1-1/2" (4cm) to ensure
that rainwater discharges into the central portion of the gutter. Once
this first course is carefully fitted and examined from the ground level
for straightness and color nuances, and adjusted accordingly, successive
courses are lapped over the ones below as the roofer works diagonally
up the roof toward the ridge. Positioning and laying tiles in a 10"
x 10" (25cm x 25cm) square may take on the average of 16-1/2 man hours.
Flat Tiles
Most flat clay tiles have one or two holes located at the top, or
on a "nib" or "lug" that projects vertically either from the face or
the underside of the tiles, for nailing the tile to the sheathing, battens,
or furring strips beneath. As successive rows of tile are installed
these holes will be covered by the next course of tiles above. Traditionally,
clay tiles on the oldest tile roofs were hung on roofing laths with
oak wooden pegs. As these wood pegs rotted, they were commonly replaced
with nails. Today, copper nails, 1-3/4" (4.5cm) slaters' nails, are
preferred for attaching the tiles because they are the longest lasting,
although other corrosion-resistant nails can also be used. Less durable
nails reduce the longevity of a clay tile roof which depends on the
fastening agents and the other roofing components, as much as on the
tiles themselves. Clay roofing tiles, like roofing slates, are intended
to hang on the nails, and nailheads should always be left to protrude
slightly above the surface of the tile: Nails should not be driven too
deeply into the furring strips because too much pressure on the tile
can cause it to break during freeze/thaw cycles, or when someone walks
on the roof.
Plain flat tiles, like roofing slates, are attached to the roof sheathing
only with nails. They are laid in a pattern overlapping one another
in order to provide the degree of impermeability necessary for the roof
covering. Because plain flat tiles overlap in most cases almost as much
of one half of the tile, this type of tile roof covering results in
a considerably heavier roof than does an interlocking tile roof which
does not require that the tiles overlap to such an extent. Interlocking
flat tiles form a single layer, and an unbroken roof covering. Although
most interlocking tiles on all but the steepest roofs can technically
be expected to remain in place because they hang on protruding nibs
from the roofing laths or battens, in contemporary roofing practices
they are often likely to be nailed for added security. In most cases
it is usually a good idea to nail at least every other tile (Fig. 12).
Pantiles
With Mission or Barrel tiles, where one half-cylinder overlaps another
inverted half-cylinder to form a cover and pan (cap and trough) arrangement,
the fastening is more complicated. While the pantiles that rest directly
on the sheathing are simply nailed in place, there are two ways of attaching
the cover tiles that rest on the pantiles. They can be secured by a
copper wire nailed to the sheathing or tied to vertical copper strips
running behind the tiles (Fig. 13). Another method requires the installation
of vertical battens or nailing strips on the roof to which the cover
tiles are nailed, or the use of tile nails or hooks, which are hooked
to the pantile below and secured with twisted copper wire.
Sometimes cement mortar, or another underlayer such as grass, moss
or straw, or hair-reinforced mortar was added under the tiles. Before
the use of felting this was a particularly common practice on some of
the plain flat tile or Spanish tile roofs with low rises that were themselves
not especially waterproof. Mortar also helped to keep driving rain from
getting under the pantiles, and it is still customary in contemporary
roofing to add a dab of cement mortar to help secure them (Fig. 14).
Ridge or Hip Tiles
At the roof ridge or hip, clay tile is usually attached to a raised
stringer with nails and a small amount of mortar, elastic cement or
mastic. The joint is sealed with a flexible flashing such as copper
or lead. Ridge tiles are often somewhat larger and more decorative than
the field tile utilized on the broad sections of the roof.
Roof Pitch and Weather are Factors in Tile Attachment
The means by which clay tile is attached to the sheathing is also
partly determined by the roof pitch. Generally the fastening requirements
increase with an increase of roof pitch. For low-pitched rises of
4"-6" (10cm-15cm) in a 12" (30.5cm) run the weight of the tiles is usually
sufficient to hold them in place on the lath by the ridge or "lug" on
the underside of the tile, with only the perimeter tiles requiring metal
clips to secure them to the sheathing. But the tiles on even these low-pitched
roofs are usually nailed for added security, and additional fastening
measures are necessary on roofs with a higher pitch, or in areas subject
to high winds or earthquakes. For steeper pitched roofs, such as towers,
7"11" (18cm-28cm), or 12"15" (30.5cm-38cm) in a 12" (30.5cm) run the
tiles are nailed and a band of perimeter tiles three to four tiles thick
is secured with clips. For roof rises over 16" (41cm) in a 12" (30.5cm)
run, and in areas prone to earthquakes or hurricanes, every tile may
be secured with both a nail and a copper or noncorrosive metal clip,
and often also with a dab of roofing mastic or mortar.
The installation of clay roofing tiles in areas with significant amounts
of snowfall-over 24" (61cm) per year-also varies somewhat from the normal
guidelines. Larger battens may be necessary, as well as additional clipping
or tying of the tile to securely attach it to the sheathing. The roof
structure itself may also need added bracing, as well as the insertion
of small snow clips or snow birds that protrude above the surface of
the tile to prevent snow and ice from sliding off the roof and damaging
the tile.
Preservation and Repair
Identifying Common Problems and Failures
While clay roofing tiles themselves are most likely to deteriorate
because of frost damage, a clay tile roof system most commonly fails
due to the breakdown of the fastening system. As the wooden pegs that
fastened the early tiles to hand-riven battens rotted, they were often
replaced with iron nails which are themselves easily corroded by tannic
acid from oak battens or sheathing. The deterioration of metal flashing,
valleys, and gutters can also lead to the failure of a clay tile roof.
Another area of potential failure of a historic clay tile roof is
the support system. Clay tiles are heavy and it is important that the
roof structure be sound. If gutters and downspouts are
allowed to fill with debris, water can back up and seep under roofing
tiles, causing the eventual deterioration of roofing battens, the sheathing
and fastening system, or even the roof's structural members (Fig. 15).
During freezing weather, ice can build up under tiles and cause breakage
during the freeze/thaw cycle. Thus, as with any type of roof, water
and improperly maintained rainwater removal and drainage systems are
also chief causes for the failure of historic clay tile roofs.
Clay tiles may be either handcrafted or machine-made; in general,
roofs installed before the end of the 19th century consist of hand formed
tiles, with machine-made tiles becoming more dominant as technology
improved during the 20th century. Clay tile itself, whether made by
hand or made by machine, can vary in quality from tile to tile. Efflorescence
of soluble salts on the surface may indicate that a tile has excessive
porosity which results from under-burning during its manufacture. Poor
quality porous tiles are particularly susceptible to breaking and exterior
surface spalling during freeze-thaw cycles. By letting in moisture,
porous tiles can permit the roof battens and roof structure to rot.
The problem may be compounded by waterproof building paper or building
felt laid underneath which can, in some instances, prevent adequate
ventilation.
Clay roofing tiles can also be damaged by roofers walking carelessly
on an unprotected roof while making repairs, or by overhanging tree
branches, falling tree limbs, or heavy hail. Broken tiles may no longer
provide a continuous waterproof surface, thereby allowing water to penetrate
the roofing structure, and may eventually result in its deterioration
if the broken tiles are not replaced in a timely manner.
Although modern, machine-made clay tiles are more uniform in appearance
than their handmade counterparts, they also have the potential for failure.
Occasionally, entire batches of mass-produced tile can be defective.
Regular Inspection and Maintenance
Broken or missing tiles, or leaks on the interior of the building,
are obvious clues that a historic clay tile roof needs repair. Even
though it may be clear that the roof is leaking, finding the source
of the leak may not be so easy. It may require thorough investigation
in the attic, as well as going up on the roof and removing tiles selectively
in the approximate area of the roof leak. The source of the leak may
not actually be located where it appears to be. Water may come in one
place and travel along a roofing member some distance from the actual
leak before revealing itself by a water stain, plaster damage, or rotted
wooden structural members.
Temporary Protection during Repair
In some instances temporary protection and stabilization may be necessary
to prevent further damage or deterioration of a historic clay tile roof.
Plywood sheets, plastic, roll roofing, or roofing felt can provide short-term
protection until repair or replacement materials can be
purchased. Another option may be to erect a temporary scaffold that
is encased or covered with clear or semitransparent polyethylene sheeting
over the entire roof. This will not only protect the exposed roofing
members during repair or until repairs can be made, but also lets in
enough natural light to enable the reroofing work to take place while
sheltering workmen from cold or wet weather.
General Repair Guidance
Once the source and cause of a leak has been identified, appropriate
repairs must be made to structural roofing members, wood sheathing,
felt or roofing paper if it is part of the roofing membrane, or possibly
to vertical roof battens to which the tiles may be attached. If the
problem appears limited to gutters and flashing in disrepair, repair
or replacement will probably require temporary removal of some of the
adjacent tiles to gain access to them. If the roofing tiles are extremely
fragile and cannot be walked on even with adequate protection (see below),
it may also be necessary to remove several rows or a larger area of
tiles and store them for later reinstallation in order to create a "path"
to reach the area of repair without damaging existing tiles. Even if
most of the tiles themselves appear to be intact but no longer securely
attached to the roof substrate due to deterioration of the fastening
system or roofing members, all the tiles should be labeled and removed
for storage. Regardless of whether the repair project involves removal
of only a few damaged tiles, or if all the tiles must be removed and
relaid, historic clay roofing tiles are inherently fragile and should
be pulled up carefully with the use of a slate ripper. The tiles can
be reattached one-by-one with new corrosion-resistant copper nails,
copper straps or tabs, "tingles', or another means after the necessary
repairs have been made to the roof.
Replacing Individual Tiles
The most difficult aspect of replacing a single broken clay roof tile
is doing so without breaking neighboring tiles. While flat shingle tiles
can generally be walked on by a careful roofer without likelihood of
much damage, high profile pantiles are very fragile and easily broken.
By using sheets of plywood, planks, or burlap bags filled with sand
to distribute weight, the professional roofer can move about the roof
to fix broken tiles or flashing without causing additional damage. Another
method involves hooking a ladder on the ridge to support and evenly
distribute the weight of the roofer.
A broken tile should be carefully removed with a slate ripper or hacksaw
blade inserted under the tile to cut the nail or nails holding it in
place. If successive layers of tile are already in place covering the
nailholes, it will not be possible to attach the replacement tile with
nails through the holes, so an alternative method of attachment will
be necessary. By nailing a tab of double thickness copper stripping
on the sheathing below the tile, the new replacement tile can be slipped
into position and secured in place by bending the copper strip up with
a double thickness of the copper over the tile. A slate hook or "tingle"
can be used in the same way. This fastening system functions in place
of nails
(Fig. 16).
When replacing hard-to-match historic tile, and if matching clay tile
cannot be obtained, it may be possible to relocate some of the original
tiles to the more prominent locations on the roof where the tile is
damaged, and insert the new replacement tile in secondary or rear locations,
or other areas where it will not show, such as behind chimney stacks,
parapets, and dormer windows. Even though replacement tile may initially
match the original historic tile when first installed, it is likely
to weather or age to a somewhat different color or hue which will become
more obvious with time. Thus, care should be taken to insert new replacement
tile in as inconspicuous a location as possible. New, machine-made clay
tile or concrete tiles should generally not be used to patch roofs of
old, handmade tile because of obvious differences in appearance.
Sources for Replacement Tiles
When restoring or repairing a clay tile roof it is always recommended
that as many of the original tiles be retained and reused as possible.
Sometimes, particularly when working with "pan and cover" type tile
roofs, while many of the "cover" tiles may be broken and require replacement,
it may be possible to reuse all or most of the "pan" tiles which are
less susceptible to damage than the "cover" tiles. But, in most cases,
unless matching replacements can be obtained, if more than about 30
per cent of the roofing tiles are lost, broken, or irreparably damaged,
it may be necessary to replace all of the historic tiles with new matching
tiles. When counting the number or percentage of missing or broken tiles
that need to be replaced, it is important to order extra tiles to allow
for
,breakage and damage during shipping and on the job site. The size
of the tiles must be noted, whether they are all the same size, the
same size but laid with different amounts of exposure to compensate
for changes in perspective, or of graduated sizes according to horizontal
rows-typical, for example, on conical or tower roofs (Fig. 17).
Many late-19th and early-20th century tiles are marked on the back
with the name of the company that made them, along with the size and
the name of that particular tile shape. Some companies that were in
business in the United States at the turn of the century are still producing
many of the traditional tile shapes, and may be able to supply the necessary
replacements. But it is important to be aware that in some cases, although
the name of a particular tile pattern may have remained the same, the
actual shape, size, thickness and profile may have changed slightly
so that the new tile does not match the historic tile closely enough
to permit it to serve as a compatible replacement for missing or broken
tiles. While such tiles may be acceptable to use on a secondary or less
prominent elevation, or to use when an entire tile roof needs replacement,
they would not be suitable to use on an area of the roof that is highly
visible.
Even if the particular tile is no longer manufactured by a company,
the original molds may still exist which can be used to make new tiles
to match the historic tiles if the quantity needed is sufficiently large
to warrant a custom order. Other companies stock and sell salvaged tile,
and keep a variety of old tiles available which can be identified and
matched by the number and company imprint on the back of the tiles.
Still other companies specialize entirely in custom-made reproduction
of historic clay tiles for a specific preservation project.
Modern clay tiles are even more varied than historic tiles. Many shapes
and styles are offered in a wide variety of colors and glazes. Several
manufacturers produce special color-blended tiles, as well as tiles
of different hues that are intended to be carefully mixed when installed.
Yet, it is important to remember that many of these modern tiles may
not be appropriate for use on historic clay tile roofs. The place of
manufacture must also be taken into consideration. For instance, tiles
made for use in a hot, dry climate may not be able to withstand wet
weather, drastic temperature changes or freeze-thaw cycles. Some of
the tile shapes, and many of the colors-especially those that are very
bright and highly glazed-are completely contemporary in design, and
do not represent traditional American styles, and thus, are not suitable
for use on historic buildings.
Repairing a Failed Fastening System
Clay roofing tiles, as noted before, frequently outlast their fastening
systems. Wood pegs rot, nails rust, and even copper nails that are not
adequately driven in can pull out of the roof's structural members.
Although it is unusual that all of the clay tiles on a roof need to
be replaced unless matching replacements cannot be obtained, it is not
uncommon for old tile roofs to be stripped of all their tiles in order
to relay the tiles with new fastenings and battens. When the fastening
system has failed, all the roof tiles must be removed and reattached
with new corrosion-resistant fasteners. If possible, all the tiles should
be numbered and a diagram should be drawn showing the location of each
tile to aid in replicating the original pattern and color variations
when the tiles are relaid. Ideally, each tile should be numbered to
ensure that it is reinstalled in its original location. But this may
not always be feasible or practical, and it may be enough simply to
group the tiles as they are removed by type and size or function-such
as field tiles, custom tiles for hips, dormers and ridges, and specially
cut pieces. This will help facilitate reinstallation of the tiles. If
all of the tiles have to be removed, it is probably a good idea to consider
installing a layer of modern roofing felt over the wood sheathing. This
will add another layer of waterproofing, while providing temporary protection
during reroofing.
Even if the tiles were originally attached with wooden pegs, it is
generally recommended that they be rehung with corrosion-resistant,
preferably heavy copper, or aluminum alloy nails or hooks. Today there
are numerous nontraditional fastening systems for clay tile roofs, and
many of them are patented. Roofing contractors and architects may have
individual preferences, and some systems may be better suited than others
to fit a particular roof shape or to meet a specific climatic or seismic
requirement. Original battens or other roof members that may have deteriorated
should be replaced to match the original using pressure-treated wood.
Additional support may be necessary, particularly if the original roof
was inadequate or poorly designed.
Replacing Flashing
Deteriorated flashing, gutters and downspouts should generally be
replaced in kind to match the historic material. Copper or lead-coated
copper, if appropriate to the building, or terne-coated stainless steel,
is often preferred for use on historic clay tile roofs because of
their durability and long lasting qualities. However, copper staining
from downspouts can sometimes be a problem on light-colored masonry
walls which should be taken into consideration when planning replacements
to rainwater removal systems. Clay tile roofs usually have an open valley
system where the tiles are separated by metal flashing at intersections
of roof sections with different angles. This makes the insertion of
new flashing quite easy, as only a few surrounding tiles must be removed
in the process. New copper flashing that is too "bright" can be made
to blend in and "mellowed" by brush-coating it with boiled linseed oil
or proprietary solutions.
Inappropriate Repairs
The most important repair to avoid is replacing broken or missing
roof tiles on a historic building with materials other than matching
natural clay tiles. Concrete, metal or plastic tiles are generally not
appropriate substitutes for clay roofing tiles. They lack the natural
color variations of clay tile, and they do not have the same texture,
shape, thickness or surface irregularities.
Although much concrete tile and composition tile is produced to resemble
the general shape, if not the exact profile, of clay roofing tiles,
concrete tile is generally too thick and also lacks the range of colors
inherent in natural clay tile. Concrete tile is not a compatible substitute
material to repair or replace individual historic clay tiles.
Patching a historic clay tile roof with roofing tar, caulk, asphalt,
pieces of metal, or non-matching clay tiles is also inappropriate. Such
treatments are visually incompatible. They also have the potential for
causing physical damage. Water can collect behind these patches, thus
accelerating deterioration of roof sheathing and fastening systems,
and during the expansion and contraction of a freeze-thaw cycle ice
buildup at patches can break surrounding tiles.
Summary
Clay roofing tile itself, when correctly installed, requires little
or no maintenance. Often, it is the fastening system used to secure
the tiles to the sheathing that fails and needs to be replaced rather
than the tiles themselves. In fact, because clay tiles frequently outlasted
the building structure, it was not unusual for them to be reused on
another building. When the fastening system has deteriorated, or the
roofing support structure has failed, clay tiles can be removed relatively
easily, necessary repairs can be made, and the historic tiles can be
relaid with new corrosion-resistant nails or hooks. Broken or damaged
tiles should be replaced promptly to prevent further damage to neighboring
tiles or to the roof structure itself.
As with any kind of historic roofing material, regular maintenance,
such as cleaning gutters and downspouts, can add to the life of a tile
roof. Additional preventive measures may include placing wire mesh over
downspout openings or over the entire gutter to prevent debris from
collecting and water from backing up. Periodic inspection of the underside
of the roof from the attic after a heavy rain or ice storm for water
stains may reveal leaks in their early stages which can be eliminated
before they escalate into larger, more serious repair problems.
If replacement tile is required for the project, it should match the
original tile as closely as possible, since a historic clay tile roof
is likely to be one of the building's most significant features. Natural
clay tiles have the inherent color variations, texture and color that
is so important in defining the character of a historic tile roof. Thus,
only traditionally shaped, clay tiles are appropriate for repairing
a historic clay tile roof.
Selected Reading
Azevedo, J. "Tile Roofing." Fine Homebuilding. No. 60 (April/May
1990), pp. 3641.
Belle, John, John Ray Hoke, Jr., and Stephen A. Kliment, editors.
Traditional Details for Building Restoration, Renovation, and Rehabilitation.
From the 19321951 Editions of [Ramsey/Sleeper] Architectural Graphic
Standards." New York: John Wiley & Sons, Inc. 1991.
Davis, Charles Thomas. A Practical Treatise on The Manufacture of
Brick, Tiles, Terra Cotta, Etc. Philadelphia: Henry Carey Baird &
Co., 1884.
Fidler, John. "Tile, Slate and Stone Roofs." Traditional Homes
Technical Information Leaflet. Number 1. 1991.
Labine, Clem. "How to Repair an Old Roof" The Old-House Journal.
Vol. XI, No. 3 (April 1983), pp. 6469
Labine, Clem, and Judith Siegel Lief. "The Rise of the Ornamental
Roof,' and "Traditional Building's Source-List of Traditional Roofing
& Specialties." Traditional Building. Vol. 5, No. 3 (May/June
1992), pp. 3546.
Melville, Ian A., and Ian A. Gordon. The Repair and Maintenance
of Houses. London: The Estates Gazette Limited, 1973.
Poore, Patricia. "Tile Roofs." The Old-House Journal. Vol.
XV, No. 5 (September/October 1987), pp. 2229.
"Special Roof Issue." The Old-House Journal. Vol XI, No. 3
(April 1983). Sweetser, Sarah M. Preservation Briefs 4: Roofing for
Historic Buildings. Washington, D.C.: National Park Service, U.S.
Department of the Interior, 1978.
Vogel, Neal A. Roofing Houses of Worship: Roofing Guidance for
Church and Temple Administrators. Information Series No. 59. Chicago:
National Trust for Historic Preservation and Inspired Partnerships,
1992.
White, Richard. Olmsted Park System, Jamaica Plain Boathouse, Jamaica
Plain, Massachusetts: Planning for Preservation of the Boathouse Roof.
Preservation Case Studies. Washington, D.C.: Heritage Conservation and
Recreation Service, U.S. Department of the Interior, 1979.
Selected
Sources of Clay Roofing Tiles
Boston Valley Terra Cotta
6860 South Abbott Road
Orchard Park, NY 14127
Custom-made architectural terra cotta and clay roofing tiles
C.C.N. Clay Roof Tiles (Canteras Cerro Negro S.A.)
8280 College Parkway, Suite 204
Ft. Myers, FL 33919
Distributors of C.C.N. clay roofing tiles from Argentina
Earth/Forms of Alfred
5704 East Valley Road
Alfred Station, NY 14803
Made-to-order reproduction clay roofing tiles
Gladding, McBean & Co.
P.O. Box 97
Lincoln, CA 95648
Manufacturer since 1875 of terra cotta and clay roofing tiles, and
custom reproductions
Hans Sumpf Company, Inc.
40101 Avenue 10
Madera, CA 93638
MADE-TO-ORDER Mission-style clay roofing tiles
International Roofing Products, Inc.
4929 Wilshire Blvd., Suite 750
Los Angeles, CA 90010
New clay roofing tiles, some suitable for historic buildings
London Tile Co.
65 Walnut Street
New London, OH 44851
MADE-TO-ORDER reproduction clay roofing tiles
LudowiciCeladon, Inc.
4757 Tile Plant Road
New Lexington, OH 43764
Manufacturer since 1880s of clay roofing tiles, and custom reproductions
M.C.A. (Maruhachi Ceramics of America, Inc.)
1985 Sampson Avenue
Corona, CA 91719
New clay roofing tiles, some suitable for historic buildings
The Northern Roof Tile Sales Company
P.O. Box 275
Millgrove, Ontario LOR 1VO, Canada
Traditional clay roofing tiles imported from England and South America
Raleigh, Inc.
6506 Business U.S. Route 20
P.O. Box 448
Belvidere, IL 61008-0448
Inventory of new and salvage clay roofing tiles
Supradur Manufacturing Corp.
P.O. Box 908
Rye, NY 1~580
Imports Spanish ("S") clay roofing tiles from France
TileSearch
P.O. Box 580
Roanoke, TX 76262
Computerized network for new and salvage clay roofing tiles
United States Tile Company
P.O. Box 1509
909 West Railroad Street
Corona, CA 91718
New clay roofing tiles, some suitable for historic buildings
Note: Measurements in this publication are given in both the U.S.
Customary System and International (Metric) System for comparative purposes.
Metric conversions are, in some cases, approximate and should not be
relied upon for preparing technical specifications.
Acknowledgements
Anne Grimmer is a senior Architectural Historian with the Preservation
Assistance Division of the National Park Service; Paul K. Williams is
a Cultural Resource Manager with the Air Force. Both authors wish to
thank the following individuals for the technical assistance they provided
in the preparation of this publication: Edna Kimbro, Architectural Conservator,
Watsonville, CA; Edwin S. Krebs, AIA, K. Norman Berry Associates, Louisville,
KY; Melvin Mann, TileSearch, Roanoke, TX; Walter S. Marder, AIA, Division
of Historical Resources, Tallahassee, FL; Gil S·nchez, FAIA,
Gilbert Arnold S·nchez, Incorporated, Santa Cruz, CA; Terry Palmiter
and Sandra Scofield, Alfred, NY; and National Park Service professional
staff members. In addition, the authors wish to thank Karin Murr Link,
who produced the drawings which illustrate this Brief.
Washington, D.C. September, 1992
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