The Preservation and Repair of Historic Clay Tile Roofs
Clay tiles are one of the most distinctive and decorativehistoric roofing materials because of their great variety ofshapes, colors, profiles, patterns, and textures. Traditionally,clay tiles were formed by hand, and later by machine extrusion ofnatural clay, textured or glazed with color, and fired inhightemperature kilns. The unique visual qualities of a clay tileroof often make it a prominent feature in defining the overallcharacter of a historic building (Fig. 1). The significance andinherently fragile nature of historic tile roofs dictate thatspecial care and precaution be taken to preserve and repair them.
Clay tile has one of the longest life expectancies amonghistoric roofing materials-generally about 100 years, and oftenseveral hundred. Yet, a regularly scheduled maintenance programis necessary to prolong the life of any roofing system. Acomplete internal and external inspection of the roof structureand the roof covering is recommended to determine condition,potential causes of failure, or source of leaks, and will help indeveloping a program for the preservation and repair of the tileroof. Before initiating any repair work on historic clay tileroofs, it is important to identify those qualities important incontributing to the historic significance and character of thebuilding.
This Brief will review the history of clay roofing tiles andwill include a description of the many types and shapes ofhistoric tiles, as well as their different methods of attachment.It will conclude with general guidance for the historic propertyowner or building manager on how to plan and carry out a projectinvolving the repair and selected replacement of historic clayroofing tiles. Repair of historic clay tile roofs is not a jobfor amateurs; it should be undertaken only by professional roofers experienced in working with clay tile roofs.
The origin of clay roofing tile can be traced independently totwo different parts of the world: China, during the NeolithicAge, beginning around 10,000 B.C.; and the Middle East, a shorttime later. From these regions, the use of clay tile spreadthroughout Asia and Europe. Not only the ancient Egyptians andBabylonians, but also the Greeks and Romans roofed theirbuildings with clay tiles, and adaptations of their practicecontinue in Europe to the present. European settlers brought thisroofing tradition to America where it was established in manyplaces by the 17th century.
Archeologists have recovered specimens of clay roofing tilesfrom the 1585 settlement of Roanoke Island in North Carolina.Clay tile was also used in the early English settlements inJamestown, Virginia, and nearby St. Mary's in Maryland. Clayroofing tiles were also used in the Spanish settlement of St.Augustine in Florida, and by both the French and Spanish in NewOrleans.
Dutch settlers on the east coast first imported clay tilesfrom Holland. By 1650, they had established t ~u ~ fullscaleproduction of clay tiles in the upper Hudson River Valley,shipping tiles south to New Amsterdam (Fig. 2). Several tilemanufacturing operations were in business around the time of theAmerican Revolution, offering both colored and glazed tile andunglazed natural terracotta tile in the New York City area, andin neighboring New Jersey. A 1774 New York newspaper advertisedthe availability of locally produced, glazed and unglazedpantiles for sale that were guaranteed to "stand anyweather." On the west coast clay tile was first manufacturedin wooden molds in 1780 at Mission San Antonio de Padua inCalifornia by Indian neophytes under the direction of Spanishmissionaries (Fig. 3).
By far the most significant factor in popularizing clayroofing tiles during the Colonial period in America was theconcern with fire. Devastating fires in London, 1666, and Bostonin 1679, prompted the establishment of building and fire codes inNew York and Boston. These fire codes, which remained in effectfor 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 thecost of clay tile, its use began to decline in much of thenortheastern United States during the second quarter of the 19thcentury. In most areas outside citydesignated fire districts,wood shingles were used widely; they were more affordable andmuch lighter, and required less heavy and less expensive roofframing. In addition, new fireresistant materials were becomingavailable that could be used for roofing, including slate, andmetals such as copper, iron, tinplate, zinc, and galvanized iron.Many of the metal roofing materials could be installed at afraction of the cost and weight of clay tile. Even the appearanceof clay tile was no longer fashionable, and by the 1830s clayroofing tiles had slipped temporarily out of popularity in manyparts of the country.
By the mid19th century, the introduction of the ItalianateVilla style of architecture in the United States prompted a newinterest in clay tiles for roofing. This had the effect ofrevitalizing the clay tile manufacturing industry, and by the1870s, new factories were in business, including large operationsin Akron, Ohio, and Baltimore, Maryland. Clay tiles were promotedby the Centennial Exhibition in Philadelphia in 1876, whichfeatured several prominent buildings with tile roofs, including apavilion for the state of New Jersey roofed with clay tiles oflocal manufacture. Tilemaking machines were first patented in the1870s, and although much roofing tile continued to be made byhand, by the 1880s more and more factories were beginning to usemachines (Fig. 4). The development of the Romanesque Revivalstyle of architecture in the 1890s further strengthened the roleof clay roofing tiles as an American building material (Fig. 5).
Alternative substitutes for clay tiles were also needed tomeet this new demand. By about 1855, sheet metal roofs designedto replicate the patterns of clay tile were being produced.Usually painted a natural terra cotta color to emulate real claytile, these sheet metal roofs became popular because they werecheaper and lighter, and easier to install than clay tile roofs.
Clay roofing tiles fell out of fashion again for a short timeat the end of the 19th century, but once more gained acceptancein the 20th century, due primarily to the popularity of theRomantic Revival architectural styles, including Mission,Spanish, Mediterranean, Georgian and Renaissance Revival in whichclay tile roofs featured prominently. With the availability ofmachines capable of extruding clay in a variety of forms in largequantities, clay tiles became more readily available across thenation. More regional manufacturing plants were established inareas with large natural deposits of clay, including Alfred, NewYork; New Lexington, Ohio; Lincoln, California; and Atlanta,Georgia; as well as Indiana, Illinois and Kansas.
The popularity of clay tile roofing, and lookalike substituteroofing materials, continues in the 20th century, especially inareas of the South and West-most notably Florida andCalifornia-where Mediterranean and Spanishinfluenced styles ofarchitecture still predominate (Fig. 6).
During the 17th and 18th centuries the most common type ofclay roofing tiles used in America were flat and rectangular.They measured approximately 10" x 6" x 1/2" (25cm x15cm x 1.25cm), and had two nail or peg holes at one end throughwhich they were anchored to the roofing laths. Sometimes a stripof mortar was placed between the overlapping rows of tile toprevent the tiles from lifting in high winds. In addition to flattiles, interlocking Sshaped pantiles were also used in the 18thcentury. These were formed
by molding clay over tapered sections of logs, and weregenerally quite large. Alternately termed pan, crooked, orFlemish tiles, and measuring approximately 14 1/2" x 91/2" (37cm x 24cm), these interlocking tiles were hung onroofing lath by means of a ridge or lug located on the upper partof the underside of each tile. Both plain (flat) tile and pantile(Sshaped or curved) roofs were capped at the ridge withsemicircular ridge tiles. Clay roofing tiles on buildings inmid18th century Moravian settlements in Pennsylvania closelyresembled those used in Germany at the time. These tiles wereabout 14"15" long x 6"7" wide (36cm38cm x15cm18cm) with a curved butt, and with vertical grooves to helpdrainage. They were also designed with a lug or nib on the backso that the tiles could hang on lath without nails or pegs.
The accurate dating of early roofing tiles is difficult andoften impossible. Fragments of tile found at archeological sitesmay indicate the existence of clay tile roofs, but the same typeof tile was also sometimes used for other purposes such aspaving, and in bake ovens. To further complicate dating, sinceclay tile frequently outlasted many of the earliest, lesspermanent structures, it was often reused on later buildings.
In addition to sheet metal "tile" roofs introducedin the middle of the 19th century, concrete roofing tile wasdeveloped as another substitute for clay tile in the latter partof the 19th century (Fig. 7). It became quite popular by thebeginning of the 20th century. Concrete tile is composed of adense mixture of portland cement blended with aggregates,including sand, and pigment, and extruded from highpressuremachines. Although it tends to lack the color permanence and thesubtle color variations inherent in natural clay tile, concretetile continues to be a popular roofing material today because itreproduces the general look of clay tile, if not always the exactprofile or proportions of historic clay tile, at a somewhat lowercost and weight. Another modern, slightly cheaper and lightersubstitute for clay tile more recently developed consists of amixture of mineral fiber and cement with pigments added to supplycolor. While these aggregate tiles also replicate the shape andappearance of clay roofing tiles, they have many of the samedissimilarities to clay tiles that are found in concrete tiles.Thus, like concrete tiles, they are seldom appropriatesubstitutes for clay tiles.
There are two types of clay roofing tiles: interlocking andoverlapping. Interlocking tiles are designed in pairs so that anextrusion 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 theroof structure. Overlapping tiles, which can also function inpairs, generally do not have any sort of "lip" and mustbe nailed in place. There is a wide range of shapes of historicclay roofing tiles, and many, sometimes with slight variations,are still produced today. There are many variations, and thecountry of origin of some of them may be revealed in their names,but there are essentially only two kinds of shapes: pantiles andflat tiles. Both pantiles and flat tiles may be eitherinterlocking or overlapping (Figs. 89).
Pantiles. The shape most commonly associated with historicclay roofing tiles is probably that of convex or rounded tiles,often grouped together generically as "pan tiles" or"pantiles." These include Spanish tiles-sometimescalled "S" tiles, or the similarly shaped Missiontiles, also known as Barrel or Barrel Mission tiles, straight ortapered, as well as Roman tiles, and their Greek variation.
Flat Tiles. Flat, shingle tiles are another type of historicclay roofing tiles. Flat tiles can be completely plain and flat,and, like roofing slates, overlap one another, attached withnails to the roof sheathing. Or they may interlock at the top andon one side. Although the "interlock" holds themtogether, most interlocking shingle tiles also have one or moreholes, usually near the top, for nailing to the roof sheathing.Flat tiles are mostly variations of English or Shingle tiles, andinclude English Shingle, Closed Shingle, Flat, Shingle or SlabShingle, as well as French tiles which have a slightly higher andmore contoured profile.
Any of the standard tile shapes may be known by a differentname in another region of the country, or in different parts ofthe world. For example, what are known as Spanish or"S" tiles in the United States, may be called SingleRoman tiles in England. Sometimes Spanish and Mission tiles areequated despite the fact that the former are usually 1pieceinterlocking tiles and the latter are single 1/2 cylinders thatoverlap. 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 asimilar vein, Spanish or "S" tiles, or Barrel tiles,might seem to be more typical of some tiles used in France thanwhat are marketed as French tiles by American manufacturers.
Today some tile manufacturers have given their own trademarkname to historic tile shapes. Other companies market uniquelyshaped "S" tiles that are more in the shape of a true,but rather low profile "s" without the customary flatportion of traditional American "S" tiles.
Field and Specialty Tile. The tiles that cover the majority ofthe flat surface of the roof are called field tile. Some roofshapes, particularly conical towers or turrets, require tiles ofgraduated sizes, and some shapes or patterns of field tile alsorequire specially shaped finish tiles to complete the roofcovering package. Other uniquelyshaped tiles were made to fitoddshaped spaces and places including dormers and valleys, roofhips, 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 andrain, and birds from nesting in the voids under the bottom row ofcurved tiles. Different patterns and designs can also be createdby combining, or mixing and matching flat tiles with dimensionaltiles.
Tile Colors. A terra cotta red is the color most commonlyassociated with historic clay roofing tiles. The reddish colorcomes from clay with a large percentage of iron oxide, and thereare many variations of this natural color to be found in tilesranging from deep reddish
browns to softer and paler oranges and pinks. Lighter buff andbeige colors, as well as black, also appear on traditionaltileroofed buildings. Buffcolored tiles were made from nearlypure fire clay, and pouring manganese dissolved in water over thetile before firing resulted in smoke brown or black glazed tiles.Toward the end of the 19th century the popularity of coloredglazes for roofing tiles increased, and their use and the range of colors continues to expand today. Most historic glazed roofingtiles are in fairly natural hues that range from reds and brownsand buffs, to blacks and purples, blues (often created withsmalt, or powdered blue glass), and a wide variety of greens(usually created with copper slag). There could be a considerablerange in the colors of tiles that were baked over a wood firebecause the temperature within the kiln was so uneven; tilesclosest to the fire cooked all the way through and turned adarker red, while tiles farthest from the flames were likely tobe smokestained, and lighter orange in color.
The method used to attach clay roofing tiles varies accordingto the shape, size and style of the particular tile. For the mostpart, traditional and modern methods of installing clay roofingtiles are very similar, except that modern practice alwaysincludes the use of wood sheathing and roofing felt. But most of the earliest clay roofing tiles were laid without benefit of woodsheathing and hung directly on roofing laths and battens thatwere nailed to the roof rafters; this practice continued up intothe mid19th century in some regions. While this method ofattachment allowed for plenty of ventilation, and made it easy tofind leaks and make repairs, it also meant that the overallwatertightness of the roof depended entirely on the tilesthemselves.
Gradually, the practice evolved of nailing roofing tilesdirectly onto continuous wood sheathing, or hanging them from"nibs" on horizontal lath that was attached to roofrafters or sheathing. Some kinds of tile, especially the laterMission or Barrel tiles were laid over vertical strips or battensnailed to the sheathing, or the tiles were fastened to woodpurlins with copper wire.
Partly because they do not always fit together very closely,some tile shapes, including Spanish, Barrel or Mission as well asother types of interlocking tiles, are not themselves completely water-repellent when used on very low pitched roofs. These havealways required some form of subroofing, or an additionalwaterproof underlayer, such as felting, a bituminous or acementitious coating. In some traditional English applications, atreatment called "torching," involved using a simplekind of mortar most commonly consisting of
straw, mud, and moss. The tapered Mission tiles of the oldSpanish missions in California were also laid in a bed of mudmortar mixed with grass or straw which was their only means ofattachment to the very lowpitched reed or twig sheathing (latia)that supported the tiles (Fig. 10).
More recent and contemporary roofing practices require thatthe tiles be laid on solid l" (2.5cm) wood sheathing feltedwith coated base sheets of at least 30 lbs., or builtup membranesor singleply roof membranes. This substantially increases thewatertightness of the roof by adding a second layer ofwaterproofing. Horizontal and vertical chalk lines are drawn toserve as a guide in laying the tile and to indicate its patterning. Most tiles are designed with one or two holes so theycan be attached by copper nails or hangers, and/or withprojecting nibs, to interlock or hang on battens or lath attachedto the base sheathing.
Before laying the tiles, the copper or lead gutters, flashingsand valleys must be installed, preferably using at least #26gauge (2024 ounce) corrosionresistant metal extending a minimumof 12" (30.5cm) under the tile from the edge, or inaccordance with the manufacturer's specifications. The long lifeand expected durability of clay tiles require that, as with theroofing nails, only the best quality metal be selected for theflashing 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 companyor roofing contractor should calculate the number of tiles neededaccording to the type of roof, and based on architect's drawingsto ensure accuracy. This should include specialty ridge and eave tiles, decorative trim, partial "squares" approximately1020 per cent allowance for breakage, and extra tiles to storefor repairing incidental damage later on. Once at the site, thetile is evenly distributed in piles on the roof, within easyreach for the roofers.
The tiles are laid beginning with the first course at thelower edge of the roof at the eaves. The method by which roofingtiles are laid and attached varies, depending on the type anddesign of the tiles and roof shape, as well as on regionalpractice and local weather conditions. A raised fascia, a cantstrip, a double or triple layer of tiles, or special"birdstop" tiles for under the eaves, may be used toraise the first row of tiles to the requisite height and anglenecessary for the best functioning of the roof (Fig. 11). Thetile is positioned to overhang the previously installed guttersystem by at least 1-1/2" (4cm) to ensure that rainwaterdischarges into the central portion of the gutter. Once thisfirst course is carefully fitted and examined from the groundlevel for straightness and color nuances, and adjustedaccordingly, successive courses are lapped over the ones below asthe roofer works diagonally up the roof toward the ridge.Positioning and laying tiles in a 10" x 10" (25cm x25cm) square may take on the average of 16-1/2 man hours.
Most flat clay tiles have one or two holes located at the top,or on a "nib" or "lug" that projectsvertically either from the face or the underside of the tiles,for nailing the tile to the sheathing, battens, or furring stripsbeneath. As successive rows of tile are installed these holeswill be covered by the next course of tiles above. Traditionally,clay tiles on the oldest tile roofs were hung on roofing lathswith oak wooden pegs. As these wood pegs rotted, they werecommonly replaced with nails. Today, copper nails, 1-3/4"(4.5cm) slaters' nails, are preferred for attaching the tilesbecause they are the longest lasting, although other corrosion resistant nails can also be used. Less durable nailsreduce the longevity of a clay tile roof which depends on thefastening agents and the other roofing components, as much as onthe tiles themselves. Clay roofing tiles, like roofing slates,are intended to hang on the nails, and nailheads should always beleft to protrude slightly above the surface of the tile: Nailsshould not be driven too deeply into the furring strips becausetoo much pressure on the tile can cause it to break duringfreeze/thaw cycles, or when someone walks on the roof.
Plain flat tiles, like roofing slates, are attached to theroof sheathing only with nails. They are laid in a patternoverlapping one another in order to provide the degree ofimpermeability necessary for the roof covering. Because plainflat tiles overlap in most cases almost as much of one half ofthe tile, this type of tile roof covering results in aconsiderably heavier roof than does an interlocking tile roofwhich does not require that the tiles overlap to such an extent. Interlocking flat tiles form a single layer, and an unbroken roofcovering. Although most interlocking tiles on all but thesteepest roofs can technically be expected to remain in placebecause they hang on protruding nibs from the roofing laths orbattens, in contemporary roofing practices they are often likelyto be nailed for added security. In most cases it is usually agood idea to nail at least every other tile (Fig. 12).
With Mission or Barrel tiles, where one halfcylinder overlapsanother inverted halfcylinder to form a cover and pan (cap andtrough) arrangement, the fastening is more complicated. While thepantiles that rest directly on the sheathing are simply nailed inplace, there are two ways of attaching the cover tiles that reston the pantiles. They can be secured by a copper wire nailed tothe sheathing or tied to vertical copper strips running behindthe tiles (Fig. 13). Another method requires the installation ofvertical battens or nailing strips on the roof to which the covertiles are nailed, or the use of tile nails or hooks, which arehooked to the pantile below and secured with twisted copper wire.
Sometimes cement mortar, or another underlayer such as grass,moss or straw, or hairreinforced mortar was added under thetiles. Before the use of felting this was a particularly commonpractice on some of the plain flat tile or Spanish tile roofswith low rises that were themselves not especially waterproof.Mortar also helped to keep driving rain from getting under thepantiles, and it is still customary in contemporary roofing toadd a dab of cement mortar to help secure them (Fig. 14).
At the roof ridge or hip, clay tile is usually attached to araised stringer with nails and a small amount of mortar, elasticcement or mastic. The joint is sealed with a flexible flashingsuch as copper or lead. Ridge tiles are often somewhat larger andmore decorative than the field tile utilized on the broadsections of the roof.
The means by which clay tile is attached to the sheathing isalso partly determined by the roof pitch. Generally thefastening requirements increase with an increase of roof pitch.For lowpitched rises of 4"-6" (10cm15cm) in a 12"(30.5cm) run the weight of the tiles is usually sufficient tohold them in place on the lath by the ridge or "lug" onthe underside of the tile, with only the perimeter tilesrequiring metal clips to secure them to the sheathing. But thetiles on even these lowpitched roofs are usually nailed for addedsecurity, and additional fastening measures are necessary onroofs with a higher pitch, or in areas subject to high winds orearthquakes. For steeper pitched roofs, such as towers,7"11" (18cm28cm), or 12"15" (30.5cm38cm) in a12" (30.5cm) run the tiles are nailed and a band ofperimeter 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 maybe secured with both a nail and a copper or noncorrosive metalclip, and often also with a dab of roofing mastic or mortar.
The installation of clay roofing tiles in areas withsignificant amounts of snowfall-over 24" (61cm) peryear-also varies somewhat from the normal guidelines. Largerbattens may be necessary, as we]l as additional clipping or tyingof the tile to securely attach it to the sheathing. The roofstructure itself may also need added bracing, as well as theinsertion of small snow clips or snow birds that protrude abovethe surface of the tile to prevent snow and ice from sliding offthe roof and damaging the tile.
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. Asthe wooden pegs that fastened the early tiles to handrivenbattens rotted, they were often replaced with iron nails whichare themselves easily corroded by tannic acid from oak battens orsheathing. The deterioration of metal flashing, valleys, andgutters can also lead to the failure of a clay tile roof.
Another area of potential failure of a historic clay tile roofis the support system. Clay tiles are heavy and it is importantthat the roof structure be sound. If gutters and downspouts are
allowed to fill with debris, water can back up and seep underroofing tiles, causing the eventual deterioration of roofingbattens, the sheathing and fastening system, or even the roof'sstructural members (Fig. 15). During freezing weather, ice canbuild up under tiles and cause breakage during the freeze/thawcycle. 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 machinemade; ingeneral, roofs installed before the end of the 19th centuryconsist of hand
formed tiles, with machinemade tiles becoming more dominant astechnology improved during the 20th century. Clay tile itself,whether made by hand or made by machine, can vary in quality fromtile to tile. Efflorescence of soluble salts on the surface mayindicate that a tile has excessive porosity which results fromunderburning during its manufacture. Poor quality porous tilesare particularly susceptible to breaking and exterior surfacespalling during freezethaw cycles. By letting in moisture, poroustiles can permit the roof battens and roof structure to rot. Theproblem may be compounded by waterproof building paper orbuilding 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 byoverhanging tree branches, falling tree limbs, or heavy hail.Broken tiles may no longer provide a continuous waterproofsurface, thereby allowing water to penetrate the roofingstructure, and may eventually result in its deterioration if thebroken tiles are not replaced in a timely manner.
Although modern, machinemade clay tiles are more uniform inappearance than their handmade counterparts, they also have thepotential for failure. Occasionally, entire batches ofmassproduced tile can be defective.
Regular Inspection and Maintenance
Broken or missing tiles, or leaks on the interior of thebuilding, are obvious clues that a historic clay tile roof needsrepair. Even though it may be clear that the roof is leaking,finding the source of the leak may not be so easy. It may requirethorough investigation in the attic, as well as going up on theroof and removing tiles selectively in the approximate area ofthe roof leak. The source of the leak may not actually be located where it appears to be. Water may come in one place and travelalong a roofing member some distance from the actual leak beforerevealing itself by a water stain, plaster damage, or rottedwooden structural members.
Temporary Protection during Repair
In some instances temporary protection and stabilization maybe necessary to prevent further damage or deterioration of ahistoric clay tile roof. Plywood sheets, plastic, roll roofing,or roofing felt can provide shortterm protection until repair orreplacement materials can be
purchased. Another option may be to erect a temporary scaffoldthat is encased or covered with clear or semitransparentpolyethylene sheeting over the entire roof. This will not onlyprotect the exposed roofing members during repair or untilrepairs can be made, but also lets in enough natural light toenable the reroofing work to take place while sheltering workmenfrom 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 theroofing membrane, or possibly to vertical roof battens to whichthe tiles may be attached. If the problem appears limited togutters and flashing in disrepair, repair or replacement willprobably require temporary removal of some of the adjacent tilesto gain access to them. If the roofing tiles are extremelyfragile and cannot be walked on even with adequate protection(see below), it may also be necessary to remove several rows or alarger area of tiles and store them for later reinstallation inorder to create a "path" to reach the area of repairwithout damaging existing tiles. Even if most of the tilesthemselves appear to be intact but no longer securely attached tothe roof substrate due to deterioration of the fastening systemor roofing members, all the tiles should be labeled and removedfor storage. Regardless of whether the repair project involvesremoval of only a few damaged tiles, or if all the tiles must beremoved and relaid, historic clay roofing tiles are inherentlyfragile and should be pulled up carefully with the use of a slateripper. The tiles can be reattached onebyone with newcorrosionresistant copper nails, copper straps or tabs,"tingles', or another means after the necessary repairs havebeen made to the roof.
Replacing Individual Tiles
The most difficult aspect of replacing a single broken clayroof tile is doing so without breaking neighboring tiles. Whileflat shingle tiles can generally be walked on by a careful rooferwithout likelihood of much damage, high profile pantiles are veryfragile and easily broken. By using sheets of plywood, planks, orburlap bags filled with sand to distribute weight, theprofessional roofer can move about the roof to fix broken tilesor flashing without causing additional damage. Another methodinvolves hooking a ladder on the ridge to support and evenlydistribute the weight of the roofer.
A broken tile should be carefully removed with a slate ripperor hacksaw blade inserted under the tile to cut the nail or nailsholding it in place. If successive layers of tile are already inplace covering the nailholes, it will not be possible to attachthe replacement tile with nails through the holes, so analternative method of attachment will be necessary. By nailing atab of double thickness copper stripping on the sheathing belowthe tile, the new replacement tile can be slipped into positionand secured in place by bending the copper strip up with a doublethickness of the copper over the tile. A slate hook or"tingle" can be used in the same way. This fasteningsystem functions in place of nails (Fig. 16).
When replacing hardtomatch historic tile, and if matching claytile cannot be obtained, it may be possible to relocate some ofthe original tiles to the more prominent locations on the roofwhere the tile is damaged, and insert the new replacement tile insecondary or rear locations, or other areas where it will notshow, such as behind chimney stacks, parapets, and dormerwindows. Even though replacement tile may initially match theoriginal historic tile when first installed, it is likely toweather or age to a somewhat different color or hue which willbecome more obvious with time. Thus, care should be taken toinsert new replacement tile in as inconspicuous a location aspossible. New, machinemade clay tile or concrete tiles shouldgenerally not be used to patch roofs of old, handmade tilebecause of obvious differences in appearance.
Sources for Replacement Tiles
When restoring or repairing a clay tile roof it is alwaysrecommended that as many of the original tiles be retained andreused 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, itmay be possible to reuse all or most of the "pan" tileswhich are less susceptible to damage than the "cover"tiles. But, in most cases, unless matching replacements can beobtained, if more than about 30 per cent of the roofing tiles arelost, broken, or irreparably damaged, it may be necessary toreplace all of the historic tiles with new matching tiles. Whencounting the number or percentage of missing or broken tiles thatneed to be replaced, it is important to order extra tiles toallow for
,breakage and damage during shipping and on the job site. Thesize of the tiles must be noted, whether they are all the samesize, the same size but laid with different amounts of exposureto compensate for changes in perspective, or of graduated sizesaccording to horizontal rows-typical, for example, on conical ortower roofs (Fig. 17).
Many late19th and early20th century tiles are marked on theback with the name of the company that made them, along with thesize and the name of that particular tile shape. Some companiesthat were in business in the United States at the turn of thecentury are still producing many of the traditional tile shapes,and may be able to supply the necessary replacements. But it isimportant to be aware that in some cases, although the name of aparticular tile pattern may have remained the same, the actualshape, size, thickness and profile may have changed slightly sothat the new tile does not match the historic tile closely enoughto permit it to serve as a compatible replacement for missing orbroken tiles. While such tiles may be acceptable to use on asecondary or less prominent elevation, or to use when an entiretile roof needs replacement, they would not be suitable to use onan area of the roof that is highly visible.
Even if the particular tile is no longer manufactured by acompany, the original molds may still exist which can be used tomake new tiles to match the historic tiles if the quantity neededis sufficiently large to warrant a custom order. Other companiesstock and sell salvaged tile, and keep a variety of old tilesavailable which can be identified and matched by the number andcompany imprint on the back of the tiles. Still other companiesspecialize entirely in custommade reproduction of historic claytiles 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 colorsand glazes. Several manufacturers produce special colorblendedtiles, as well as tiles of different hues that are intended to becarefully mixed when installed. Yet, it is important to rememberthat many of these modern tiles may not be appropriate for use onhistoric clay tile roofs. The place of manufacture must also betaken into consideration. For instance, tiles made for use in ahot, dry climate may not be able to withstand wet weather,drastic temperature changes or freezethaw cycles. Some of thetile shapes, and many of the colors-especially those that arevery bright and highly glazed-are completely contemporary indesign, and do not represent traditional American styles, andthus, are not suitable for use on historic buildings.
Repairing a Failed Fastening System
Clay roofing tiles, as noted before, frequently outlast theirfastening systems. Wood pegs rot, nails rust, and even coppernails that are not adequately driven in can pull out of theroof's structural members. Although it is unusual that all of theclay tiles on a roof need to be replaced unless matchingreplacements cannot be obtained, it is not uncommon for old tileroofs to be stripped of all their tiles in order to relay thetiles with new fastenings and battens. When the fastening systemhas failed, all the roof tiles must be removed and reattachedwith new corrosionresistant fasteners. If possible, all the tilesshould be numbered and a diagram should be drawn showing thelocation of each tile to aid in replicating the original patternand color variations when the tiles are relaid. Ideally, eachtile should be numbered to ensure that it is reinstalled in itsoriginal location. But this may not always be feasible orpractical, and it may be enough simply to group the tiles as theyare removed by type and size or function-such as field tiles,custom tiles for hips, dormers and ridges, and specially cutpieces. This will help facilitate reinstallation of the tiles. Ifall of the tiles have to be removed, it is probably a good ideato consider installing a layer of modern roofing felt over thewood 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 withcorrosionresistant, preferably heavy copper, or aluminum alloynails or hooks. Today there are numerous nontraditional fasteningsystems for clay tile roofs, and many of them are patented.Roofing contractors and architects may have individualpreferences, and some systems may be better suited than others tofit a particular roof shape or to meet a specific climatic orseismic requirement. Original battens or other roof members thatmay have deteriorated should be replaced to match the originalusing pressuretreated wood. Additional support may be necessary,particularly if the original roof was inadequate or poorlydesigned.
Deteriorated flashing, gutters and downspouts should generallybe replaced in kind to match the historic material. Copper orleadcoated copper, if appropriate to the building, or ternecoatedstainless steel, is often preferred for use on historic clay tileroofs because of
their durability and long lasting qualities. However, copperstaining from downspouts can sometimes be a problem onlightcolored masonry walls which should be taken intoconsideration when planning replacements to rainwater removalsystems. Clay tile roofs usually have an open valley system wherethe tiles are separated by metal flashing at intersections ofroof sections with different angles. This makes the insertion ofnew flashing quite easy, as only a few surrounding tiles must beremoved in the process. New copper flashing that is too"bright" can be made to blend in and "mellowed" by brushcoating it with boiled linseed oilor proprietary solutions.
The most important repair to avoid is replacing broken ormissing roof tiles on a historic building with materials otherthan matching natural clay tiles. Concrete, metal or plastictiles are generally not appropriate substitutes for clay roofingtiles. They lack the natural color variations of clay tile, andthey do not have the same texture, shape, thickness or surfaceirregularities.
Although much concrete tile and composition tile is producedto resemble the general shape, if not the exact profile, of clayroofing tiles, concrete tile is generally too thick and alsolacks the range of colors inherent in natural clay tile. Concretetile is not a compatible substitute material to repair or replaceindividual historic clay tiles.
Patching a historic clay tile roof with roofing tar, caulk,asphalt, pieces of metal, or nonmatching clay tiles is alsoinappropriate. Such treatments are visually incompatible. Theyalso have the potential for causing physical damage. Water cancollect behind these patches, thus accelerating deterioration ofroof sheathing and fastening systems, and during the expansionand contraction of a freezethaw cycle ice buildup at patches canbreak surrounding tiles.
Clay roofing tile itself, when correctly installed, requireslittle or no maintenance. Often, it is the fastening system usedto secure the tiles to the sheathing that fails and needs to bereplaced rather than the tiles themselves. In fact, because claytiles frequently outlasted the building structure, it was notunusual for them to be reused on another building. When thefastening system has deteriorated, or the roofing supportstructure has failed, clay tiles can be removed relativelyeasily, necessary repairs can be made, and the historic tiles canbe relaid with new corrosionresistant nails or hooks. Broken ordamaged tiles should be replaced promptly to prevent furtherdamage to neighboring tiles or to the roof structure itself.
As with any kind of historic roofing material, regularmaintenance, such as cleaning gutters and downspouts, can add tothe life of a tile roof. Additional preventive measures mayinclude placing wire mesh over downspout openings or over theentire gutter to prevent debris from collecting and water frombacking up. Periodic inspection of the underside of the roof fromthe attic after a heavy rain or ice storm for water stains mayreveal leaks in their early stages which can be eliminated beforethey escalate into larger, more serious repair problems.
If replacement tile is required for the project, it shouldmatch the original tile as closely as possible, since a historicclay tile roof is likely to be one of the building's mostsignificant features. Natural clay tiles have the inherent colorvariations, texture and color that is so important in definingthe character of a historic tile roof. Thus, only traditionallyshaped, clay tiles are appropriate for repairing a historic claytile roof.
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 Manufactureof Brick, Tiles, Terra Cotta, Etc. Philadelphia: Henry CareyBaird & Co., 1884.
Fidler, John. "Tile, Slate and Stone Roofs." TraditionalHomes Technical Information Leaflet. Number 1. 1991.
Labine, Clem. "How to Repair an Old Roof" TheOldHouse Journal. Vol. XI, No. 3 (April 1983), pp. 6469
Labine, Clem, and Judith Siegel Lief. "The Rise of theOrnamental Roof,' and "Traditional Building's SourceList ofTraditional Roofing & Specialties." TraditionalBuilding. Vol. 5, No. 3 (May/June 1992), pp. 3546.
Melville, Ian A., and Ian A. Gordon. The Repair andMaintenance of Houses. London: The Estates Gazette Limited,1973.
Poore, Patricia. "Tile Roofs." The OldHouseJournal. Vol. XV, No. 5 (September/October 1987), pp. 2229.
"Special Roof Issue." The OldHouse Journal.Vol XI, No. 3 (April 1983). Sweetser, Sarah M. PreservationBriefs 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 Guidancefor Church and Temple Administrators. Information Series No.59. Chicago: National Trust for Historic Preservation andInspired Partnerships, 1992.
White, Richard. Olmsted Park System, Jamaica PlainBoathouse, Jamaica Plain, Massachusetts: Planning forPreservation of the Boathouse Roof. Preservation CaseStudies. Washington, D.C.: Heritage Conservation and RecreationService, U.S. Department of the Interior, 1979.
Boston Valley Terra Cotta
6860 South Abbott Road
Orchard Park, NY 14127
Custommade 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
Madetoorder 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
Madetoorder Missionstyle 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
Madetoorder reproduction clay roofing tiles
4757 Tile Plant Road
New Lexington, OH 43764
Manufacturer since 1880s of clay roofing tiles, and customreproductions
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 SouthAmerica
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
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 theU.S. Customary System and International (Metric) System forcomparative purposes. Metric conversions are, in some cases,approximate and should not be relied upon for preparing technicalspecifications.
Anne Grimmer is a senior Architectural Historian with thePreservation Assistance Division of the National Park Service;Paul K. Williams is a Cultural Resource Manager with the AirForce. Both authors wish to thank the following individuals forthe technical assistance they provided in the preparation of thispublication: 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 Sanchez, Incorporated, Santa Cruz, CA;Terry Palmiter and Sandra Scofield, Alfred, NY; and National ParkService professional staff members. In addition, the authors wishto thank Karin Murr Link, who produced the drawings whichillustrate this Brief. Washington, D.C. September, 1992Thispublication has been prepared pursuant to the National HistoricPreservation Act of 1966, as amended, which directs the Secretaryof the Interior to develop and make available informationconcerning historic properties. Technical Preservation Services(TPS), Heritage Preservation Services Division, National ParkService prepares standards, guidelines, and other educationalmaterials on responsible historic preservation treatments for abroad public.