from asbestos to zinc, roofing for historic buildings, national … · 2010-08-31 · produced...

Asbestos-CementShingles

The Asbestos Shingle, Slate, and Sheathing Companytouted the advantages of their shingles with depictionsof successful installations in their 1927 promotionalcatalog and price list. (The Catalog ofJohns-Manville Building Materials, Home Owners'Catalogue, A Guide to the Selection of BuildingMaterials Equipment and Furnishings, F. W. DodgeCorporation, 1936. Courtesy of The Sweet'sGroup-The McGraw-Hill Companies, Inc.)

In the United States,mechanized production ofasbestos-cement shinglesbegan in the first decades ofthe 20th century, followingAustrian Ludwig Hatschek'sinvention of a process in 1900to manufacture rolled andpressed asbestos-cementsheets. Hatschek's patent,reissued in United Stated in1907, led to a rapidproliferation of the newshingles. One early Americanmanufacturer, Eternit, tooktheir company name from thetitle Hatschek had given hisprocess.

Made from asbestos, aninorganic, fibrous mineral, and Portland or hydraulic cement, asbestos shingleswere lightweight, economical, and fireproof. Manufacturers promoted theirshingles as substitutes for traditional roofing materials such as slate, wood, andclay.

Manufacturers of asbestos-cement shingles andother asbestos building products appealed toarchitects and builders directly with extensiveadvertising campaigns. These drawingsaccompanied Architects's Specification included ina publication of the Asbestos Shingle, Slate &Sheathing Company. [click image for larger view]

The Asbestos Shingle, Slate andSheathing Company proclaimedin 1910: " ...these AsbestosSingles or Slates are soimmeasurably superior in pointof practical merit to that of anynatural slating that nothingremains to be said."

A variety of shingle colors couldbe created by adding pigments tothe wet mix before pressing or byrolling pigments onto thesurfaces of shingles. Colorsimitating slates, including IndianRed and Newport Gray, werecommon, but many other colorswere available. Manufacturersassured potential customers thattheir shingles were colorfast.Unfortunately, many earlyasbestos-cement shingles fadedover time, causing Columbiaprofessor H. Vandervoort Walshto exclaim in 1922: "For thisreason we see on every hand red

asbestos-shingle roofs which have bleached to sickly and thirsty pinks."

ConcreteRoofing Tile

Not all cementitious roofing products wereasbestos-based. Concrete roofing tiles, which date fromthe 1840s, were produced in Germany by Adolph Kroher,a manufacturer of cement and concrete products, whodeveloped a machine and process for pressing concretetiles that resembled shingles. In the United States, as theconcrete industry developed in the first decade of the 20thcentury, cast-in-place concrete roofing systems - andsystems assembled with concrete slabs - evolved. TheAmerican Cement Tile Manufacturing Company, forinstance, advertised "Cementile," a large (2 feet by 5 feetby 1 1/2 inches) steel-reinforced cement tile roofing, orslab, in the 1929 issue of Sweet's ArchitecturalCatalogue. "Cementile" was offered as a flat sheet forsheathing or as an interlocking tile for a finished,watertight roof covering. Such roofing products foundprincipal application for industrial buildings. Smallerconcrete roofing tiles were available in the United Statesfrom companies such as Hawthorne in Chicago by thelate1920s. Hawthorne's roofing tiles, available in nofewer than fourteen colors, simulated Spanish and FrenchClay tiles. Unlike asbestos-cement shingles, which werenailed in place, concrete tiles were interlocking and laidon hanger strips. Hip and ridge tiles were nailed inposition and holes were then pointed with matchingmortar.

From Asbestos to Zinc, Roofing for Historic Buildings, National Park Service

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Johns-Manville promoted the direct application of theirasbestos-cement shingles over worn roofing in this1936 catalog. The Dutch Lap roof being applied herewas easy to install and utilized a metal "clincher" toanchor exposed corners. (Home Owners' Catalogue,A Guide to the Selection of Building MaterialsEquipment and Furnishings, F. W. DodgeCorporation, 1936. Courtesy of The Sweet's Group-TheMcGraw-Hill Companies, Inc.) [click image for largerview]

The hydraulic pressingprocess enabled the shinglesto be given a texture, such asa rough rustic surface or oneimitating weathered wood.The many styles and sizes ofasbestos-cement shinglesavailable, made possibleroofs laid in various methodsincluding American, DutchLap, and French (known inseveral variants ashexagonal, honeycomb ordiamond). The Frenchmethod was particularlypopular for asbestos roofing,capitalizing on the economyof the material itself bylaying it in an efficientmanner requiring minimaloverlap. Installation ofasbestos shingles was similarto slate. Shingles could bepunched, filed, or trimmed tosize in the field by roofingcontractors. Companies suchas behemoth Johns-Manvilleand The Asbestos Shingle,Slate, and Sheathing inAmbler in Pennsylvaniapromoted asbestos shinglesnot only for new constructionbut also for roofing overexisting roofs.

In addition to shingles,corrugated asbestos-cementsheathing, sometimes calledasbestos building lumber, was produced by many manufacturers as a substitutefor corrugated iron roofing. Used principally for industrial applications,corrugated asbestos could be laid directly on steel roof purlins. Industrialbuildings in particular benefited from the fireproofing qualities ofasbestos-cement.

Both asbestos-cement shingles--and siding--were produced into the 1980s,testimony to their popularity and affordability. The countless buildings withthis roofing material also attest to the durability of the product.

Chicago-based Hawthorne Roofing Tile Company originallymanufactured its tile from slabs by a hand-process. These concreteroofing tiles depicted in the 1929 Sweet's Architectural Catalogimitated French and Spanish clay tiles. They were produced withautomated power-driven equipment, and the colors were impregnatedon the tile surface. (Sweet's Architectural Catalogue, 1939.Courtesy of the Sweet's Group, McGraw Hill Companies, Inc.) [clickimage for larger view]

Heritage Preservation Services


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Asphalt ShinglesAsphalt shingles have three major components: asphalt, felts and coloredmineral or ceramic granules. Asphalt is a byproduct of petroleum distillationand also occurs in natural deposits. This dense mixture of hydrocarbonsprovides the waterproofing for the shingle. The felt fibers reinforce andstabilize the asphalt,

The Barber Asphalt Co. featured their use ofnatural asphalt mined from Trinadad Lake in thepromotion of their shingles. [click image for largerview]

while the granule aggregatesprotect the assembly from sun,wind, rain and minor foottraffic.

The roots of asphalt shinglescan be found in compositionroofing that developed in theUnited States in the mid-19thcentury. In the last quarter ofthe 19th century thesite-layered components ofbuilt up roofing were adaptedto produce a factory assembledproduct of long strips.Packaged in rolls this material, once called "ready roofing," is nowcommonly known as "roll roofing." Though naturally occurring asphalt wasused early as a waterproof coating, most built-up roofing systems relied onthe more abundant coal tar. Asphalt, however, could be processed to bemore solid than coal tar, and this solidity was necessary to facilitate thetransition from a site fabricated system to a preassembled product. Despitethe abundant and affordable asphalt from a growing petroleum industry, theuse of natural asphalt was a point of product promotion at least as late as1930.

Slate used for the surface aggregate determinedthe colors of early shingles. [click image for largerview]

The first asphalt shingles wereproduced in1903 by a roofingcontractor and manufacturer ofprepared asphalt roofing.Herbert M. Reynolds of GrandRapids, Michigan, hand cutrolls of "stone surfaced" rollroofing into individual shingles.Early shingles were typicallyrectangular or hexagonal. Thecolors, usually red, green orblack, were limited by thenatural materials used for thegranular surface.

The popularity of this productled to the proliferation of shapes and sizes and attachment systems, some ofwhich were patented. The multi-tab strip shingle was a significantdevelopment that quickly emerged. It offered the traditional effect of a smallshingle with lower installation costs. By 1906 Bird and Son was marketing anotched shingle that had the appearance of two shingles when installed.

Numerous factors contributed to the increased use of asphalt shingles in the20th century. Made of non-strategic materials and easier to transport thanwood or slate, they met the constraints imposed during World War I. Moreflame resistant than wood, they were promoted in response to a 1916publication of the National Board of Fire Underwriters urging the

Shapes

Shapes manufactured by the Flintkote Company during the1940s.

[click images for larger views]


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Sears, Roebuck and Co. promoted the quality ofasphalt shingles used on many of the homes in their1926 Catalogue of Houses. (Courtesy of TheAnthenaeum of Philadelphia and Dover Publications,Inc. New York.) [click image for larger view]

elimination of woodshingles as a fire hazard.Additionally, asphaltshingles gained a costadvantage over othermaterials. Asimprovements inmanufacturing processesmade asphalt shinglescheaper, increased laborcosts made installation oftraditional materials moreexpensive.

The variety of shingleshapes and sizes peaked by1930, and by 1935 allmajor manufacturers wereoffering a 12 by 36 inchmultiple tab shingle that isthe standard today. At thesame time the introductionof ceramic granules

allowed a wider range of color choices that were often mixed to produce ablended shingle. The most significant recent change in the product itself isthe replacement of organic felts with fiberglass mats resulting in a stronger,more durable shingle.



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Clay TileThe origins of clay tile can be found in both China and the Near East, withsurviving artifacts of roofing tile dating to 2,500 BC. From these locations, itspread throughout Asia and Europe. European settlers brought this tradition tothe New World, and

The tile roof on Stadt Huys (City Hall), New Amsterdam mayhave been imported, but by the time of its construction in1641-42 tile was probably available from a tile yard up theHudson in Rensselaerwyk. (Image courtesy of the Museum ofthe City of New York)

the earliest settlementslike those on RoanokeIsland in NorthCarolina, Jamestown inVirginia, and St. Marysin Maryland haveyielded specimens ofroof tiles fromarcheologicalinvestigations. Tile wasalso used very early bythe Spanish and Frenchin the South and West.

Both time and place areimportant determinantsin the history of tileroofing in America.Tiles were firstimported, but by 1650they were beingproduced in the upper

Hudson River Valley, and several factories were in operation at the time of theAmerican Revolution. Fire was probably the single most important factor inpopularizing tile for roofing in this country. Devastating urban fires in the 17thcentury prompted regulations that encouraged the use of tile as a fireproofroofing. The use of tile roofing began to decline during the first quarter of the19th century as new fire resistant materials became available and tile roofswere viewed as clumsy and unattractive. However, by the middle of the 19thcentury, the popularity of revival styles, particularly Italianate, Gothic, andRomanesque, created new interest in tile roofs.

The barrel tile roof on Vizcayacontributes to the image of anItalian Renaissance palace sograndly realized in this Miami,Florida mansion completed in1916.

The development of architectural terra cotta asa significant building material, themechanization of tile production and thegrowth of rail transport aided a gradualresurgence of tile roofing. It was during thefirst few decades of the 20th century that therevival styles, drawn from the Mediterraneanand the American Southwest, gave tile itsbroadest use. Today tile can most commonly befound in the Southwest and coastal Southwhere its suits both the popular architecturalimages and regional climates.

Tiles are distinguished by their shape and the way they overlap. The simplestare flat tile laid like shingles with staggered joints and less than half theirsurface exposed to weather. A tile system made up of alternating convex andconcave or flat surfaces, generally referred to as pantile, may be formed byseparate tiles (Barrel, Mission, Greek, Roman) or a single S-shaped tile(Spanish). These are laid with less overlap of eachcourse than a shingle tile but include a side to side overlap. Interlocking tileshave mated ridges and grooves at their edges, thereby reducing the amount ofoverlap needed to achieve a weathertight surface. Reducing the lap decreasesoverall weight of the roof and the need for heavier framing. The interlockingfeature was only practical with the precision brought by late 19th century

Manufacturing

Roofing tile begins as raw clay that is processed bydrying, pulverizing, mixing with water and kneading. It isthen shaped into tiles, dried and fired. In the latter half ofthe 19th century mechanization was introducedincrementally to what was largely a manual operation.Even as steam power was applied to the rollers thatpulverized the clay and the pug mill that mixed andkneaded it, clay continued to be pressed into molds byhand. In the 1870s machines were developed thatdelivered and mechanically pressed slices of clay into amold. The installation of such presses at the Celadonplant in Alfred, New York, reportedly increased dailyproduction tenfold. Other advances allowed shapes suchas a shingle or barrel tile to be cut directly fromextrusions, a process commonly used today.

The kilns depicted in this drawing from an 1876 atlas have beenloaded with tile and the open ends walled up with bricks. Fires forsuch kilns were lighted and kept slowly burning for the first five hours,and then progressively increased for the next thirty-three hours.Toward the end of the firing, the mouths of the kiln were stopped withashes to prevent the flow of air from cooling the oven too quickly. Atypical kiln consumed approximately four tons of coal per firing toproduce hard fired tiles. (click image for larger view)


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Outside of the Southwest, these tiles depicted in an1884 publication are typical of what were in commonuse at that time. The diamond is an interlocking tilewhile the others are simply shingle tiles with shapedbutts. [click image for larger view]

advances in manufacturing. Itbecame common for mostflat tiles as well as surfacegrooved French tiles and isalso a feature of somepantiles.

Most clay tiles are nailed orwired to sheathing or battens,but lugs on the back of sometiles allow the weight of thetile itself to hold it in placeon low slope roofs. Mortar issometimes added,particularly on pantiles, tohold tile in place and makethe system more watertightand wind resistant. Thebarrel tiles of the southwestwere historically laid in a fullbed of mud mortar withoutadditional fasteners. Tile as amaterial often outlasts itsattachments, if not thebuilding itself, a point madein an 1884 treatise, Bricks,Tile, Terra Cotta, Etc.: "After

doing service on one structure it can be taken off and used on other buildings."


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Composition

Composition or built-up roofing is a multi-ply system of fabric or paper, aviscous waterproofing substance, and a mineral aggregate. Historically,various materials have been used for each of these components. Paper,pasteboard, canvas, burlap, and felt have all served as the base membrane.These materials were often dipped in the waterproofing coating before beingapplied to the roof. The availability of felt in rolls facilitated the mechanizationof this saturation process, and felt became the standard base. Pine tar, naturalasphalt, coal tar and asphalt were the major materials to be effective as thewaterproofing that saturated the base sheets and adhered the layers. Sand,gravel or slag provided the top surface. Though there is no evidence of theirsuccess, numerous other materials were tried as components, many as part ofpatented formulas: woven strips of paper or twine, sawdust, china clay, plasterof Paris, cattle hair, gum shellac, boiled linseed oil, boiled fish oil, and blood.

This advertisement offering both roofing materials andinstallation appeared in the late 1860s. It touted themany advanatages of a composition roof. [click imagefor larger view]

Pine tar and gravel werecombined for roofing both inEurope and the United Statesin the 1870s. In 1800 pine tarwas applied to canvas at theOctagon House inWashington, D. C., where itprovided the roof coveringfor seventeen years.Evidence of similar systemsused elsewhere in the early19th century is very limited.In the 1840s a methodlearned from a roofer inNewark became the basis fora roofing business begun inCincinnati by Samuel M. andCyrus M. Warren. They metwith success, as did others inthe northeast, applying roofsof heavy paper, covered withpine tar and sprinkled withsand. The significance of theWarrens was the innovationthey brought to the system.From experiments begun in1847, they successfullyreplaced increasingly costlypine pitch with coal tar, aby-product of manufacturingilluminating gas from coal.Their continued developmentof the product and expansionto other cities assured theWarrens' status as leaders inthe industry. They were the first in the 1850s to distill coal tar, producing asuperior refined tar. Later they found that natural asphalt from Pitch Lake inTrinidad could produce an easy-to-mix roofing pitch when combined withpetroleum tar, a by-product of oil refining.

The potential of composite roofing was apparent to many, and the number ofrelated patent applications exploded in the 1860s and 1870s. Thedevelopments in composition roofing were well timed to meet the mid-19thcentury increase in the use of flat and low-sloped roofs. The only alternative

Standards

As the materials and technology of composition roofingevolved, the number of manufacturers and installersproliferated. There was little done in the 19th century toassure the quality delivered by either. Making mattersworse, many companies asserted that their products couldbe applied by anyone. As a result, many roofs performedpoorly. Because composition roofing was amulti-component system of varied materials and methods,successful performance was hard to predict.

Samual Barrett, a Chicago roofing product manufacturer,made the first significant effort to set standards for theindustry. "Barrett Specifications" were compiled in 1906,providing minimal guidelines for the materials andapplication of a gravel or slag roof. His generic

(Sweet's Architectural Catalogue, 1929. Courtesy of The Sweet'sGroup, The McGraw-Hill Companies, Inc.) [click image for larger view]


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for such roofs at that time was metal, which depended on the performance ofthe many fabricated seams that joined the small sheets. The relative merits ofmetal and

The specification for this built-up roof being advertisedin 1929 called for it to be: "Applied only by themanufacturer or by approved roofing contractors." Thematerials consisted of asphalt-impregnatedasbestos-based roofing felt and asphalt-based roofingcement. "No slag or gravel is ever used or needed on aJohns-Manville Roof." [click image for larger view]

composition roofing wereconstantly debated. HenryHudson Holly writes in1878: "Metals are the bestcovering for roofs that areinclined to beflat...composition - such astar or other materials - wewould not advise on goodwork, as its only merit is itscheapness." Ignition andspread of fire were importantissues in the debate. A 1911test by UnderwritersLaboratories rated the fireretardant qualities of "goodslag and gravel roofs" in aclass with inferior roofingmaterials. Nevertheless, in1912 the National Board ofFire Underwriters consideredapproved composition roofstogether with metal, slate andtile the best for fireproofconstruction. The issueseems to have been settledin1916 when compositionroofs met the requirementsof both fireproof and fireretarding classes of theBoard's rating system.Built-up roofing came to dominate the commercial roofing market and remainsin use today.

specifications were later made specific to a system ofBarrett products, the whole of which he backed up with abond. Other manufacturers followed his lead promotingtheir products with brand-specific specifications. In 1916Barrett tightened his quality control by offering theguaranty bond only on roofs applied by contractors whomhe approved. Other companies went further and onlybonded installations that their own inspectors oversaw.By the1920's, detailed, lengthy texts of brand specificspecifications filled manufacturers' product information.Manufacturers' specifications and approved contractorscontinue to be a part of the commercial roofing industry.


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MetalsMetals are useful both as the roof surface itself, and as important componentssuch as flashings, valleys and gutters on roofs of other materials. Themalleability of metal allows it to be formed and joined making it useful forweatherproofing the junctures and angles on roofs. These same properties alsomake it suitable for roofing curved and irregular surfaces and for roofingwhere the pitch is too low for simple overlapping material to providewaterproofing.

This advertisement from an 1888 publication ofhouse designs, Homes of Today, offeredstamped shingles in four materials. [click image forlarger view]

As with other roofing materials,the earliest uses of metals forAmerican roofing employedimported products. Lead, copperand tin plate most often camefrom Great Britain, while the firstzinc came from Belgium. Asmines and mills opened in theUnited States, domesticproduction replaced imports. Inthe case of tin, the success ofdomestic production depended onthe advantage of a tariff onimported tinplate imposed by theMcKinley Bill of 1890.

Several factors contributed to thepopularity of metal roofingthroughout much of the 19th andearly 20th centuries-it was lighterthan slate or tile, it offered morefire protection than wood, andmost metals were less expensivethan slate or tile.

Metals are applied to roofs asshingles and as pre-formed and

site-formed sheets. The first metal shingles were small flat rectangles;surviving examples from 1819 at the University of

The corrugated sheets of "Patent Galvanized Iron"produced by Marshall Lefferts & Brother areshown in their 1854 catalog, where it is pointedout that the supporting framing may be one-fourthas heavy as would be required for slate. [clickimage for larger view]

Virginia in Charlottesville wereinterlocked at the sides withfolded edges and simply lappedat top and bottom. Not until the1870s was mass productionapplied to metal shingles.Stamping sheets of metal was aninnovation that added rigidity toa thin material and facilitatedinterlocking edges, reducingneeded lap and preventing windlift. Patterns were frequentlypatented and were produced iniron, tinplate, galvanized steel orcopper.

Sheets of iron were firstpre-formed by corrugation in England in 1828. American manufacturers wereproducing corrugatedroofing from both plain and galvanized iron by mid-19th century. Corrugationadded stiffness, making the material self-supporting over longer spans andeliminating the need for sheathing or closely-spaced framing. Thus, corrugated

AluminumThe small amount of aluminum manufactured beforethe turn of the century limited its application as abuilding material. Its early use in 1890 on the roof ofPhiladelphia's City Hall combined it with copper, andit quickly failed. By the 1920s the material was betterunderstood, and Alcoa was marketing both rolledaluminum sheets and an interlocking shingle forroofing in natural and painted finishes. Difficult tosolder, aluminum roofing relied on mechanical jointsand pitch to shed water.

CopperThe New York City Hall (1764) was a notable earlyuse of copper for roofing. Though copper roofs wereinstalled on many important buildings in the early1800s, it was infrequently used until the latter 19thcentury, when the Lake Superior mines opened inMichigan's Upper Peninsula. Even then copper wasmore often used for flashings, gutters and downspoutsthan for roofing. Copper has always been anexpensive choice for roofing, but it is easily worked,does not need a coating and weathers attractively.These factors all contribute to copper's use most oftenand to greatest advantage on the ornamental roofs ofmajor public buildings.


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This illustration from the 1893 catalog of aPhiladelphia manufacturer describes theapplication of a roof made from their iron or steelthat had been seamed into rolls at the factory,from sheets measuring 26x104 iinches. Thetechnique would have been the same for a roof oftinplate, terne plate or copper. [click image forlarger view]

iron was well suited forinexpensive, quickly assembledbuildings, making it a commonmaterial for the construction thataccompanied the California GoldRush. Later in the century,manufacturers offered flat sheetswith edges pre-formed forstanding seams or in a V shape aseconomical alternatives to onsitefabrication.

Unlike the simple lappedinstallation used for corrugated orV-edge sheets, most site-formedmetal roofing utilizes variousfolded, interlocking joints tocreate a weatherproof covering.Metals that can be fused (lead) orsoldered (tin, terne, zinc, copper)can have sealed joints, thusremoving slope as a factor in thewater-shedding performance ofthe assembly. Solder was usuallyapplied to seal interlocked seamsthat had been folded flat. Flatseams joined small sheets ofmetal to cover curved shapes orvery low-sloped roofs. They werealso used to create long strips of

a metal such as tinplate, which was only available as small sheets. When thelong strips were laid parallel to the slope of a roof (minimum 2 in 12 slope),the long edges could be joined without solder if the joints were raised abovethe rest of the roof surface as a rib. Usually the adjacent edges were foldedover each other creating a standing seam. Many metals were used for thiscommon roof. Variations on the system formed the seam over battens or usedseparate cap pieces to join the bent edge flanges. Although requiring slightlymore material, a standing seam better accommodates the expansion andcontraction of metal than does a flat seam roof.

Copper was put to effective use on the roof of the 1913 HandleyLibrary in Winchester, Virginia. (NPS photo) [click image forlarger view]

metals continued. . .


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IronBoth iron and steel without any plating wereused for roofing. The Philadelphia home ofthe mill owner who rolled the first sheet ironin the United States was roofed in thematerial around 1794. Iron replaced slate onthe White House in 1804. Because it wasavailable in large sheets, rather than thesmall sheets used for plated material, itrequired fewer joints. Some manufacturersproduced factory painted material, butlate19th century accounts indicate that paintwas an inadequate defense against thecorrosive effects of the atmosphere inindustrial regions.

LeadThe earliest use of lead for roofing in thiscountry may have been at Rosewell, an18th-century plantation house atWhitemarsh, Virginia. It was widely usedbefore the American Revolution forflashings, downspouts and gutters on thebest buildings. In the United States, leadnever achieved the popularity it had inEurope. Installed on early Federal buildingsin Washington, D.C., it failed to performwell. Expansion and contraction due totemperature changes produced fatigue, andon steep roofs the effect of gravity causedcreep.In the 20th century lead foundadditional application as a coating for bothsteel and copper.

ZincRolled sheet zinc appeared in the UnitedStates in 1816, as roofing in New York andas downspouts and gutters in Baltimore.Though more than seventy houses in NewYork had zinc roofs by 1837, it was out offavor by 1840. The popularity of thematerial was cyclical in the next decades,never matching iron and steel with theirvarious coatings.

Coated Ferrous MetalsPlating protected the base metal from rust and allowed thematerial to be soldered.

Tin andTerneTin-plated iron appeared as a roof coveringin the United States at the beginning of the19th century. Thomas Jefferson chose it forMonticello in 1800. Tin was often referredto as "bright tin" to distinguish it from thelead-tin mixture, terne (meaning "dull"inFrench). Because the plating processrequired that the base iron be dipped intomolten tin, it could only be produced insmall sheets. The sheets measured 10 by 14inches in the 1830s, but by the 1870s,advances in manufacturing increased the sizeto 20 by 28 inches. Tin's availability andreasonable cost made it a very commonroofing through much of the 19th century. Itcould be quite durable, but only if kept wellpainted.

Painting the verandah roof in stripes following theseams in the metal was a fashionable treatmentbefore the Civil War. Manufacturers and technicalmanuals recommended painting the underside of themetal as well as applying two or three coats to the top.Paints of iron oxide in linseed oil and white lead paintwere variously recommended. Since the iron oxideproduced a red or brown color, the stripes depictedwould have required a tinted white lead paint.(Courtesy of The Athenaeum of Philadelphia) [clickimage for larger view]

Terneplate was first produced in UnitedStates in New York in 1825. Joseph Truman

GalvanizedIron or steel are galvanized by coating themwith zinc. Rather than producing the simplecoating created by tinplating, a rust resistantalloy of the two metals forms on the surface.In 1839, two years after galvanizing waspatented in Europe, the material was used onthe roof of the Merchants Exchange inManhattan. Though the sheet iron was handdipped in the zinc, much as it was in tin,larger sheets were used (24 by 72 inches inthe 1850s). This meant fewer joints, andwhen used as corrugated sheets, lesssupporting framing. Even as the productionof galvanized iron and steel roofing productsincreased, the price remained higher thanthat of other metals. The price differentialdid not shrink sufficiently for galvanizedroofing to exceed tin and terneplate inpopularity until the 20th century.

EnameledEnameled steel as a building componentcame to this country by way of Germany atthe end of the 19th century. Shingles ofenameled steel were exhibited by a Germanindustrialist at the 1893 World's ColumbianExposition. The first American productionwas in 1924 by the Columbian Enamelingand Stamping Company, which roofed ahouse in Terra Haute, Indiana, withenameled shingles. Commercial marketsdeveloped by 1930, and enameled shinglesbecame popular for use on service stationsand chain restaurants. Except for the 2500Lustron houses manufactured in the late1940s, the material was rarely used inresidential applications.


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Downing describes the chevron patterned roof of hisDesign XXXI, "Villa in the Pointed Style," from TheArchitecture of Country Houses published in 1850:"The roof may be covered with zinc laid on a ribbedsheathing, without soldering so as to allow it toexpand and contract without detriment."(Courtesy ofThe Athenaeum of Philadelphia) [click image forlarger view]

of Philadelphia patented the lead coating oftinplate in 1831. Later production combinedthe lead and tin into a single coating. Calledvariously "leaded plate," "roofing tin", and"roofing plate," terne was cheaper than apure tin coating, but its properties were verysimilar. Domestic production of terne wastwice that of tin when it was chosen to roofthe buildings of the 1893 World's ColumbianExposition. In the next few decades ternereplaced tin completely in Americanproduction as steel replaced iron as the basemetal.

Emphasizing its two trademark components thisenameled shingle was described in the 1929Sweet's Architectural Catalogue: "The baseArmco ingot iron and the two coats of Pemcoglass fused together at 1600 degrees F., producea roofing tile extremely durable and of permanentbeauty." (Sweet's Architectural Catalogue,1929. Courtesy of The Sweet's Group, TheMcGraw-Hill Companies, Inc.) [click image forlarger view]


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SlateSlate is a fine grained crystalline rock metamorphosed from bedded deposits ofclay and silt. It can be worked into shingles readily because it has two lines ofbreakability: cleavage and grain. These occur generally at right angles to eachother and are independent of the original bedding planes. The structure of

Front elevation of a dwelling published in Supplementto Bicknell's Village Builder. A specification for one ofthe designs included this direction for the French roof:"Slate the sides of the roof with slate 5 x 12 inches,cornered as shown on elevation, nailed with galvanizednails; all hips and valleys to be flashed with tin in thebest manner." (Courtesy of The Athenaeum ofPhiladelphia)

the bedding remains in someslate deposits as visiblebands running across thecleavage. Known as ribbons,these bands may be eitherweaker or harder than thesurrounding slate. Slate'sdurability as roofing is due toits high strength, lowporosity and low absorptionrate. Specific mineralcomponents are responsiblefor the various colors: carbon(black), hematite (red andpurple), chlorite and ferrousiron oxide (green). Otherminerals, consideredimpurities (calcite and ironsulfides), are slowlytransformed by weatheringinto gypsum, which expandsand causes the slate todelaminate.

Slate has been used as aroofing material in Europe for hundreds of years, with surviving examplesdating to the 8th century. From the 17th to the 19th centuries, most of theroofing slate used in America was imported from North Wales, where slatequarrying was a major industry. Although the first commercial slate quarry inthe United States

was opened in 1785 in PeachBottom, Pennsylvania, theindustry was limited andlocal until the second half ofthe 19th century. At that timethe industry grew andmatured in response to agrowing population,advancements in quarryingtechnology, an expanding railsystem, and the immigrationof Welsh slate workers toAmerica.

The United States became aslate exporter after the CivilWar, as quarries opened inVermont, New York,Virginia, and Pennsylvania.Architectural styles of thisperiod emphasized prominentroof lines and decorativepatterns, details that werewell suited to the varied

Quarrying

Until the 1870s the quarrying of slate changed little fromwhat is illustrated by Diderot in the PictorialEncyclopedia of Science Art and Technology of 1762.Blocks were separated from the floor of the quarry usingpicks, wedges, prybars and gunpowder, taking maximumadvantage of the natural seams in the rock. Windlassesand simple cranes employed man or horse power to liftblocks of slate from the pit. With the IndustrialRevolution came mechanical drills and steam-poweredstone channeling machines and hoists. Waste associatedwith blasting was reduced and efficiency increased.Subsequent advances were marked by the introduction ofthe wire saw in 1926 and the diamond belt saw in 1988.

Mineralogie, Ardoises D'Anjou. Travail de la Carrierre Ouverte etOutils. Revuell de Planches, sue Les Sciences, Les Arts Liberaux,et Les Arts Mechaniques, Avec Explication, Diderot-D'Alembert.(Courtesy of NewsBank, Inc.) [click image for larger view]


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The Vendor Slate Co. had ten quarries inPennsylvania, Vermont and New York in 1929.(Sweet's Architectural Catalogue, 1929. Courtesy ofThe Sweet's Group, The McGraw-Hill Companies, Inc.)[click image for larger view]

colors and shapes availablein slate. Properties such asnonflammability, durability,minimal maintenance costs,and aesthetic value madeslate all the more desirable.

Its primary drawback was its weight, making shipping costly and requiringsubstantial roof framing.

Between 1897 and 1914 production peaked. Later use of slate often employeddifferent thicknesses and colors, and unevenly cut or aligned butts to producepicturesque effects suitable for English revival styles popular in the early 20thcentury. After 1915 widespread use of slate roofing declined in the UnitedStates, due in part to a lack of skilled labor, but more importantly, due to thedevelopment of modern, mass produced materials such as asphalt shingles,which seemed the more economical alternative.

"Not all that glitters is gold. Not allthat looks like slate is good slate."claims the Bangor Slate Co. ofEaston, Pennsylvania. They issuedthis certificate in 1906 emphasizingthe source of slate as an indicationof quality. [click image for largerview]

A slate is typically attached to woodensheathing with two nails driven throughprepunched holes, though as with tile, it maybe wired or screwed to steel angles on a steelframed roof. At the end of the19th centuryasphalt saturated felt laid over the woodsheathing became a standard part of mostslate roof installations. Slate is installed withan overlap that depends on the slope of theroof and requires a minimum pitch(generally 4 inches of rise per 12 inches ofrun) to effectively shed water. Particularly incoastal areas slate can be found laid inmortar, providing extra protection againstwind driven rain.

Today slate continues to be quarried domestically as well as being importedfrom Europe, China and South America.


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Wood ShinglesWood roofing shingles were commonplace in early America not

"The drawing was taken in a swamp which has beenworked, for its buried logs, for the fifty years past; andthe scattering trees which are seen are only such ashave escaped the workman's axe. The levers, spade,and other tools of the shingler are seen, and he is inthe act of cutting up the floated log. Several bolts, orblocks in form for splitting into shingles, are lying on theground in front of him. In the background, a man isseen shaving the shingles. The workmen go over thesame ground again and again, and find new logs eachtime." (From George H. Cook, Geology of the Countyof Cape May, State of New Jersey [Trenton: Printed atthe Office of the True American, 1857], 78). [clickimage for larger view]

only because of theabundance of timber, butalso because of the relativeease with which they couldbe fabricated and installed.Made from the heartwoodof a variety of locallyavailable trees, earlyshingles were hand splitwith a mallet and froe andthen dressed or smoothedwith a draw knife to ensurethey would lay flat on theroof. The introduction ofwater and, then, steampowered saws in the early19th centuryrevolutionized the shingleindustry by makingpossible the massproduction of uniformlycut and smoothly finishedshingles that required nohand dressing. As early as1802, for example, N.Combes of Lamberton,New Jersey, informed thepublic that he now had ashingle dressing machinethat had been newly invented by 'D[avid] French of Connecticut. Thismachine at one stroke shaves the Shingle complete; at the second stroke itjoints the same, and this done much more complete than it is possible tohave it done by hand, in the usual way (The True American, Trenton,December 6, 1802). The number of inventions for new types of shinglemachines, as well as refinements to existing ones, quickly multiplied as thecentury advanced; at least nineteen patents were issued in 1857 alone forshingle making machines.

Despite such technological advances, hand split shingles never entirelydisappeared. In fact, during most of the 19th century a thriving split shingleindustry existed in southern New Jersey. Interestingly, much of the woodused in these shingles came from white cedar logs that had been buried inswamps and then "mined" or raised by shinglers who probed the area forsuitable logs. Reportedly a good shingler could tell merely by smell whethera log had been blown down or broken off, the former being the moredesirable since it was less likely to be decayed. Once loosened from thepeat, the log floated in the water, where it was sawn into blocks and thensplit into shingles. An expert worker could mine and shave up to 1,000shingles a week. Besides supplying local markets, South Jersey's minedshingles were shipped to cities and towns up and down the Delaware River,including Philadelphia.

Although wood shingles received strong competition from other roofingmaterials in the 19th century, they enjoyed renewed popularity in the late19th and early 20th centuries with the introduction of the various revivalstyles of architecture. Wooden shingles were steamed and bent to resemblethatched roofs on Tudor Revival homes, laid in evenly spaced overlapping

Coatings

To enhance their durability, wood roofing shingles weresometimes given a protective coating. Pine tar, boiledlinseed oil, and boiled fish oil (probably whale oil) were allused, often in combination with various pigments for color.The roofs of many famous buildings, including MountVernon,the Governor's Palace in Williamsburg, andIndependence Hall, Congress Hall, and Carpenters' Hall inPhiladelphia were all painted historically. Red and thered-brown shade known as "Spanish brown" wereespecially popular colors in the 18th and early 19th century.During the Victorian period,

A view of Mount Vernon, c.1792; oil on canvas.Courtesy of the National Gallery of Art, Washington,DC; Gift of Edgar William and Bernice ChryslerGarbish. [click image for larger view]

many painting manuals recommended painting or stainingroofs in dark colors. Sherwin Williams, for example, in its1885 book House Painting commented that a roof shouldnot be painted a light color, but some dark color that willstrongly contrast with the paint on the main part of thebuilding." In the early 20th century, many manufacturersbegan coating their shingles with creosote oil, tinted inshades of brown, green, red, and gray. Shingles of one colorcould be laid on a roof to produce a uniform appearance or,


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horizontal rows on Colonial Revival houses, and used with abandon on theroofs and sides of Shingle Style buildings. Today, although wood shinglesrepresent a relatively small percentage of the roofing market, they remain afashionable material for custom houses as well as restoration projects.

The wood shingles on the roof ofthis Tudor Revival house (left)

were steamed and bent toresemble thatching. To aid

architects and contractors to laysuch special effects shingles

properly, manufacturers like theCreo-Dipt Company, Inc. of NorthTonawanda, New York, publishedroof details, like those in the 1923

Sweet's ArchitecturalCatalogue (below). (Photograph

courtesy of NPS; "CountryCottage Roof".) [click image for

larger view]

for a variegated effect, two or more shades could becombined. Of course, wood shingles could be, and oftenwere, left uncoated. In such instances they would graduallyassume what Calvert Vaux described in his 1857publication Villas and Cottages as "a soft, pleasant, neutraltint that harmonizes with any color that may be used in thebuilding."



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Gutters andDownspoutsGutters and downspouts are the principal means by which water is conveyedoff a roof and away from a building. There is little evidence that they wereemployed at first in the Colonies but by the early 18th century their use

An early wooden gutter with brackets is illustrated inFrancis William Edmonds' painting, The ThirstyDrover,1856. Rain barrels or cisterns were commonrepositories for rain water and were ubiquitouselements in the colonial landscape. (Image courtesy ofthe Nelson-Atkens Museum of Art, Kansas City,Missouri. Purchase: Nelson Trust). [click image forlarger view]

had become an acceptedpractice on finer buildings.

Simple styles of woodengutter from the 18th centuryinclude the V-shaped gutter,formed by fastening thelong sides of two boardstogether or the rectilinearshaped gutter formed byhollowing out a hewn log.Wooden pins or wroughtiron brackets were used tofasten the gutter to the eaveor side of the building."Drop gutters" ordownspouts were woodenand were formed byfastening four boardstogether or by hollowingout a hewn block of woodor log. Improvements weremade to wooden gutters over time and they became not only practicaldrainage components but aesthetically pleasing architectural details withclassical profiles.

An 1871 photograph of the corner of 3rdStreet, south of Walnut in Philadelphiashows a number of rain water conductorsystems. In the lower left corner is ametal roof with a built-in gutter lined withmetal; on the far right is a building with awood shingle roof and a built-in gutterwith exposed downspout; and in thecenter is a four story brick building withbuilt-in gutters and internal downspouts.(Print & Picture Collection, The FreeLibrary of Philadelphia) [click image forlarger view]

They remained popular in the NewEngland area until World War II.Wooden downspouts however werefound to leak and were eventuallyreplaced by metal ones.

Lead was another material used duringcolonial times for making gutters anddownspouts. The half-round was theearliest form of hanging metal gutterand was made from sheets of hammeredlead formed around wooden poles into aU-shape shaped trough. When hung, thegutter was loosely suspended from theroof eaves by straps. Early metaldownspouts were typically cylindricalin shape and made of lead. Somedownspouts ran only partially down thesides of buildings while others droppedto just above grade and onto splashstones, into cisterns, or intounderground drainage systems. With theadvent of the Revolutionary War, themilitary need for lead for the Coloniesencouraged the use of other metals likecopper, tinplate, and terneplate.

Built-in gutters were introduced into the

Snow Guards

Snow guards or snow brakes, as they are sometimes called,began appearing on slate and metal roofs of New Englandin the late 1800s. The tremendous quantities of snow andice that accumulated on these roofs made the wood ormetal diverter, typically attached above the front entry, anineffective tool in preventing the snow from sliding downthe roof. With snow guards in place, the snow wouldeventually blow away or remain until it melted. Not onlywas the risk of damage to objects and persons belowavoided, but the banking of snow and ice at the eaves wasprevented, thus eliminating the chances of backwater andconsequent leaks, as well as a straining of the gutterstructure. (Sweet's Architectural Catalogue, 1906. Courtesyof the Sweets Group, the McGraw-Hill Companies, Inc.)

Folsom Snow Guard Company of Boston, Massachusetts advertisedthree models of snow guards in the 1906 Sweet's Indexed Catalogueof Building Construction. [click image for larger view]


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American vocabulary with high-style 18th century buildings. Characterizedby its integration with a cornice (either open or closed), built-in gutterspreserved the architectural detail of the cornice while providing a practicalsolution to storm water drainage.

The pole gutters on the roof at 757 SwansonStreet, Philadelphia in 1868 divert rainwater toa short cylindrical downspout. Moisture damageis evident on the wall of the building below theend of the pipe where there is no downspoutextension. (Print & Picture Collection, The FreeLibrary of Philadelphia) [click image for largerview]

Historically these were boxesmade of wood, the bottom ofwhich was sloped, and, wherepossible, lined with metal, usuallylead. As buildings grew in heightand complexity in the 19thcentury, cast iron or tile internaldownspouts or leaders wereintroduced to invisibly movewater away from the roof and intosubterranean drainage systems.

Another type of metal gutter seenon early high style buildings ofthe 18th century was the pole orstop gutter. In its simplest form, apole gutter was made by foldingup one edge of the metal sheetuntil the upright edge wasperpendicular when placed uponthe roof. It was fastened near theeaves to channel water directly offthe roof or to a downspout.Wooden boards were oftensecured just below the metalgutter to keep it from flattening out. Pole gutters were popular until the early20th century.

During the Industrial Revolution hanging metal gutters became very popular.Supplier's catalogues offered seven different styles, custom and stock,imitating classical moulding profiles in eight-foot lengths. By the 20thcentury these were available in terne, copper, galvanized iron, galvanizedsteel, monel, aluminum, and even vinyl. The "K-style" gutter trough, easilyidentified by its ogee profile, became a standard in the 1940s.


Parknet

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RoofingTodayThe manufacturing of roofing materials and installation practices today draw upon theexperience of the past 300 years. While this is particularly true with restoration workon historic buildings, it is also evident with new construction work. The strong markettoday for

The first ply of hot applied, built-up roofing is installedover perlite insulation board. The system is carefullyinstalled to accommodate locations of roofpenetrations and rooftop mechanical equipment.(Photograph courtesy of Wiss, Janney Elstner andAssociates)

"substitute" materials that conveysome of the same visual qualities oftraditional roofing reflects oursociety's appreciation of historicarchitecture.

Building code changes, performancerequirements, code constraints, newtechnologies, and modern buildingpractices are just a few of the factorsthat have contributed to an everevolving roofing industry. For historicbuildings, the greatest opportunity totake advantage of these changes iswith low slope roofing. Because ofthe low slope design, these areas areoften not visible from grade and thusthere is less concern with matchingthe appearance of the original roofingthan with more visible steep sloped roofing. Some of the materials and systemsoriginally used on historic low slope roofs (such as canvas) are not necessarilywatertight or durable, and therefore are not appropriate choices for reroofing. The fourmain types of low slope roofing systems today are fully adhered, mechanicallyfastened, loose laid and ballasted, and protected membrane. Each of these systems hascertain advantages and disadvantages with respect to wind, fire, resistance tomechanical damage, ease of installation, thermal value, resistance to ponded water, andcompatibility with existing roof deck and structural components. Some systemsstrongly reflect traditional roofing practices while others are very contemporaryapproaches.

Built-Up RoofsToday's built-up roofing systems incorporate traditional as well as contemporarymaterials, and contemporary improvements for installation techniques. Modernbuilt-up roofs are fully adhered assemblies of multiple reinforcing plies (organic,fiberglass, or nonwoven polyester mats) that are directly embedded in layers of

hot asphalt or coal tar. The finishedassemblies are often covered with gravel.Asphalt roofs can be left smooth surfacedbut must be coated to protect them fromdirect sunlight and also to provide a firerating. Coal tar bitumen, used on manyhistoric buildings, offers superiorresistance to ponded water.

Single PliesSingle ply roofs today involvecontemporary materials and installationtechniques. Single ply roofs consist of asingle layer of synthetic materials, 30 to80 mils (.030 to .080 inches) thick, thatcan incorporate a reinforcement layer ofpolyester or fiberglass. Single ply roofs

Tools andEquipment forInvestigationand Installation

Many traditional tools are still used in roofing,but equipment for investigation and installationhas changed. Modern techniques forinvestigation include nuclear moisture meters,infrared thermal imaging, capacitance meters,moisture monitoring systems, and specialmeasuring devices.

New tools and equipment for installation includeelectrical lifting equipment such as cranes andsmall mechanized hoists, as well as special safetyequipment such as special ladders and fallprotection, and mechanical fasteners such as nailguns. These new tools have significantlyfacilitated roofing work.

The first ply of hot applied, built-up roofing isinstalled over perlite insulation board. Thesystem is carefully installed to accommodatelocations of roof penetrations and rooftopmechanical equipment. This single plymembrane with an isolation felt material (visibleat left) is covered by concrete masonry unitpavers, in this example of a ballasted system. Thepavers are interlocked with plastic tabs. Alongthe wall at the right is a PVC clad metal baseflashing.

This investigatoris using anuclear moisturemeter to identifyareas ofmoisture in theroof system. Thenuclear moisturemeter is mostappropriate foruse with gravel


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This single ply membrane with an isolation feltmaterial (visible above) is covered by concretemasonry unit pavers, in this example of aballasted system. The pavers are interlocked withplastic tabs. Along the wall at the right is a PVCclad metal base flashing.(Photograph courtesy ofWiss, Janney Elstner and Associates)

can be ethylene propylene diene monomer(EPDM), polyvinyl chloride (PVC),thermoplastic polyolefin (TPO), orhypalon, which begins as a weldablethermoplastic and becomes rubber-like asit cures. Single ply roofs are categorizedas thermosets, thermoplastics, andplasticizers. They can be fully adhered,

mechanically fastened, loose laid and ballasted, or placed under an extrudedpolystyrene insulation board as a protected membrane roof.

Modified BitumenModified bitumen roofs involve some traditional materials, but use modern fabricationmethods, and traditional or more contemporary installation techniques. Modifiedbitumen roofs are made from prefabricated rolls of modified asphalt (or coal tar)reinforced with a fiberglass or polyester reinforced mat. Rubber-modified asphalts,such as styrene-butadiene-styrene (SBS) materials, are granular surfaced and arenormally installed in two or more plies using mopping asphalt, cold adhesives, or torchwelding. Plastic-modified asphalts such as atactic polypropylene (APP) systems aresmooth or granular surfaced and can be heat welded or laid in cold adhesive.

Metal RoofsMetal roofs have a long history of use, although improvements have occurred in shopfabrication methods and new sealant materials. Metal roofs are available in a widevariety of rib configurations, colors, and slope configurations. Architectural systemsuse an underlying deck to provide structural support, while structural standing seammetal roofs provides an integral supporting frame. Structural systems can be used toretrofit an existing flat roof deck to provide improved drainage. Sealant is required atvalleys, gutters, and drains, to ensure watertightness.

Sprayed Polyurethane FoamSprayed polyurethane foam is a contemporary system that is sometimes appropriate foruse on historic structures. Sprayed polyurethane foam (SPF) accepts a variety ofsubstrates and is readily adapted to recovering existing flat or low sloped roofs. Thisroofing can be designed to incorporate increased slope for better drainage. The foamalso serves as insulation. A smooth or granular coating is usually applied to provideprotection from sunlight.

surfacedbuilt-up, EPDM, and modified bitumen roofing systems. Thesystem is most accurate when the rigid insulation beneaththese systems is uniform in thickness. (Photographcourtesy of Wiss, Janney Elstner and Associates)


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