clay tiles

Roof tiles are designed for use as overlapping, water- shedding roof components that rely on the slope of a roof substrate to effectively shed water.

Clay and concrete roof tile can be categorized by their shapes: flat or profile. Products designated as flat tiles may be plain slab tiles or interlocking tiles. Roof tile profile typically is expressed as the ratio of tile height (sometimes rise) to its width. Profile may be further separated into low, medium and high profiles. A low profile classifica-tion typically is applied to flat tiles or tiles with 1/2-inch or less variation (rise) in top surface features or texture. Medium profile tiles are those with a height to width ratio of 1:5 or less. High profile tiles have a height to width ratio greater than 1:5. The ratio for pan and cover tiles is measured in installed condition. Standard mate-rial specifications for tile provide classifications by type wherein types of tile are differentiated by profiles. The classifications for clay tile are not the same as classifica-tions for concrete tile. See Figure 3-1 on page 126.

Additionally, tile shapes commonly are categorized as follows:

Plaintile

Panandcovertile

Interlockingtile(interlockingtilesmaybehigh-,medium- or low-profile tiles and flat tiles)

S-tile

See Figures 3-2 on page 127 and 3-3 on page 128 for common tile shapes.

Plain Tile: Plain tiles also are referred to as flat-slab or shingle tiles. They are noninterlocking pieces meant to be laid in a double coverage pattern similar to asphalt shin-gles, wood shakes and slate. With plain tile applications, head lap is necessary. The customary head lap dimensions are 2 inches or 3 inches. Plain tile thicknesses range from 1/2 of an inch to 3/4 of an inch. Leading edges usually are square, but some are manufactured with rounded and other profiles. Some plain tiles have a roughened end that

CHAPTER 3CLAY AND CONCRETE TILE

The NRCA Roofing Manual: Steep-slope Roof Systems2013

125The NRCA Roofing Manual: Steep-slope Roof Systems2013Clay and Concrete Tile Roof Systems | Chapter 3Clay and Concrete Tile

has a hand-made appearance. A wide variety of surface treatments are applied during manufacture, including smooth, glazed, scored, grooved, sanded, ash-coated or others, that create textures to achieve traditional ap-pearances. Figure 3-4 on page 129 lists some common plain tile dimensions and corresponding piece counts per square required to obtain a 2-inch head lap. Tile weight per applied square will vary depending on tile thickness and composition, and head lap selected. Manufacturers

published information can be consulted when calculating the dead load for a specific tile roof system.

Pan and Cover Tile: Pan and cover tiles also are referred to as barrel tiles or mission tiles in some regions. Pan and cover tiles are installed with one tile laid concave and the adjacent laid convex. See Figure 3-2 for common shapes. Pan and cover tiles can be straight or tapered and are available in a variety of surface textures.

126 The NRCA Roofing Manual: Steep-slope Roof Systems2013Clay and Concrete Tile Roof Systems | Chapter 3Clay and Concrete Tile

Figure 3-1: Roof tile classification by profile


ROMAN TILE

GREEK TILE

FLAT INTERLOCKING TILE

FLAT OR SHINGLE TILE

FRENCH INTERLOCKING TILETWO-PIECE BARREL OR MISSION TILE

PAN AND COVER TILE

INTERLOCKING TILEPLAIN TILE

S-TILE

S-TILE

Figure 3-2: Common clay tile profiles


S-TILE

INTERLOCKING CHANNELED TILE

SIMULATINGSLATE

SIMULATINGSHAKE

PLAIN TILE

FLAT OR SHINGLE TILETWO-PIECE BARREL OR MISSION TILE

S-TILE

PAN AND COVER TILE

INTERLOCKING TILE

Figure 3-3: Common concrete tile profiles

Pans and covers are laid in a variety of ways. Pans can be laid tight to one another at the sides or spaced apart, pro-viding a reduced side lap by the covers. Straight barrel pans are sometimes used with tapered covers for added applica-tion flexibility and aesthetics. Some covers have clipped top corners that fit against clipped bottom corners of the pans, which provides for a tight fit. Tile weight per ap-plied square will vary depending on tile thickness and composition, and application pattern selected. Manufac-turers published information can be consulted when cal-culating the dead load for a specific tile roof system.

Interlocking Tile:Interlockingtilesarelaidinasinglethickness with only a course-to-course overlap. The sides are channeled or ribbed so that neighboring tiles are lapped. Various interlock styles are used to assist in align-ing tiles and minimize water migration at side laps. The heads and butts also may interlock, or a simple overlap may be used. With some styles of interlocking tiles, the exposed portion is flat and the surface can be smooth or textured. The thickness at the butt of the flat styles ranges from 1/2 of an inch to 2 inches. Some interlocking tiles are profiled, and the contours help direct runoff away from the interlocking sides of the tiles. Some contoured tiles are available that have the appearance of pan and cover tiles. Contours add strength to tile. Reinforcing ribs on the undersides add strength and reduce weight. Typically, the height of interlocking profile tile ranges from 2 inches to 6 inches. Virtually all concrete tiles and some clay tiles are interlocking. Figure 3-5 lists some common interlock-ing tile dimensions and corresponding piece counts per square required for a 3-inch course-to-course overlap. Tile weight per applied square will vary depending on tile thickness and composition, and application pattern selected. Manufacturers published information can be consulted when calculating the dead load for a specific tile roof system.

S-tile: S-tile refers to the tile profile. Sometimes, S-tile also is referred to as one-piece pan and cover. S-tiles are

laid in a single layer with a course-to-course overlap. Thickness varies, but typical tile thickness is about 1/2 of an inch. Surfaces are available in smooth or a variety of textures.Insomestyles,theconvexportionislargerthanthe concave. The concave portions may be rounded or flattened in contour. Figure 3-6 lists some common S-tile dimensions and corresponding piece counts per square re-quired for a 3-inch course-to-course overlap. Tile weight per applied square will vary depending on tile thickness and composition, and application pattern selected. Man-ufacturers published information can be consulted when calculating the dead load for a specific tile roof system.

3.1 Clay and Concrete Tile Materials

Roof Tile Materials: Roof tiles are manufactured from two general types of material: clay and concrete.

Clay Roof Tile: High-quality clay and shale deposits are selected for mining based on their mineral compositions, which are responsible for the hardness, durability and color of the finished product. The raw material is crushed and ground into fine powder. The materials are mixed, and the clay is wetted and worked to become a homog-enous mass of the proper plasticity. The clay is extruded, cut to size, and formed or pressed into the various shapes and styles of clay roof tile.

A wide variety of surface textures and some ceramic matte colors may be applied before drying and firing. The natu-ral red color of clay tile results from the firing process. High-gloss ceramic glazes may be applied to fired tile,


Figure 3-4: Common plain tile dimensions

Overall Length x Width

Exposure Length x Width

Approximate Pieces/Square

12 inch x 7 inch 5 inch x 7 inch 412

15 inch x 7 inch 61/2 inch x 7 inch 317

18 inch x 8 inch 71/2 inch x 8 inch 240Figure 3-5: Common interlocking tile dimensions




11 inch x 83/4 inch 8 inch x 8 inch 225

14 inch x 9 inch 11 inch x 81/4 inch 158

17 inch x 123/4 inch 14 inch x 11 inch 94

Figure 3-6: Common S-tile dimensions




131/4 inch x 93/4 inch 101/4 inch x 81/4 inch 171

131/2 inch x 11 inch 101/2 inch x 91/2 inch 144

181/2 inch x 121/2 inch 151/2 inch x 9 inch 104

19 inch x 14 inch 16 inch x 12 inch 75

which, in turn, is refired to add durable color and gloss to the surface.

Clay tiles are fired in kilns at temperatures ranging from 1800 F to 2000 F. The period of firing ranges from 20 to 24 hours, with the tile being held at maximum tempera-tures for three to six hours. The raw material character-istics, amount of heat and duration of firing affects the resultant strength, moisture-absorption properties and overall quality of the finished product.

Concrete Roof Tile: Concrete tile manufactured in North America is produced in automated extrusion plants. Typically, semidry concrete mixes composed of Portland cement, water, and sand or fine aggregate are mixedandthenextrudedunderhighpressure.Insomeregions, tile is made from standard and lightweight con-crete mixes to produce different weights of concrete tile. Some moist mixes are compacted by vibration and tamp-ing, and then molds are used to form the concrete to the desired shape. Various additives may be included during mixing to improve strength, reduce water-absorption properties or control curing time.

Typically, color is added by mixing mineral oxide pig-ments with the base materials or by spraying the color on the surface after the concrete has been extruded. Cementitious glazes containing pigments also are used where glazed surfaces are desired. Concrete tile is put into a kiln for drying. The surfaces of some tiles also are sprayed with sealers.

Tile should be allowed to cure before shipping so design strengths and physical properties may be achieved. As with other concrete products, the curing process contin-ues over a longer period of time.

Roof Tile Physical Characteristics: The follow-ing physical characteristics are key to clay and concrete roof tiles performance in service.

Water Absorption: Tiles absorption properties are an indicationofitsabilitytoendurefreeze-thawcycling.Ifthe absorption value is low, the less water the material can hold and the less likely the tile will be damaged during freeze-thaw cycles. Water absorption of tile is expressed as a percentage of the dry weight. Dense, well-baked clay tile may have absorption values under 2 percent when fully vitrified. The absorption values of some clay tile

range up to 10 percent. Concrete tile absorption values range from 3 percent to 20 percent. Sealers sometimes are used to reduce porosity. The service lives of the sealers and some surfacings should be considered during the roof design phase as should the possible need to reseal the tiles surface in the future.

Breaking Strength: Tile strength is important to resist breakage during shipment and installation; withstand service traffic over the roof after installation; and resist breakage during wind, seismic activity and hail storms. Strength typically is measured as breaking load. For roof tiles, this ranges from 250 pounds to 1,000 pounds and is predicated on thickness, cross-section profile, raw mate-rial quality, and firing or curing process. Typical breaking loads are about 650 pounds for clay tile and about 400 pounds for concrete tile.

Freeze-thaw Resistance: Weather conditions create dif-ferent demands on roof tiles long-term ability to func-tion successfully. Resistance to freeze-thaw cycles is im-portant where the tile is expected to withstand repetitive freezing and thawing. Cracking and/or spalling ultimately will result in premature roof system failure.

Some types of tile are graded for their resistance to frost action. ASTM Standard C1167, Standard Specification for Clay Roof Tiles, provides grades of clay tile, and each has a different resistance to freeze-thaw cycles. Grade 1 provides resistance to severe frost action, Grade 2 provides resistance to moderate frost action and Grade 3 provides negligibleresistancetoanyfrostaction.ASTMInterna-tional roof tile material specifications provide a defini-tion for a weathering index, which is used to quantify the magnitude of frost action effect on roof tile weathering. A diagram of the weathering index contours superim-posed over a map of the continental U.S. provided in the specifications is reproduced in Figure 3-7. ASTM C1167 associates its tile grade classifications with the weathering index as follows: Grade 1weathering index of 500 and greater; Grade 2weathering index of 50 to 500; and Grade 3weathering index less than 50.

Designers should specify roof tile materials of a grade appropriate for the weathering index.

Tiles resistance to weathering cannot always be predicted with certainty when using the physical tests available. The best indication of tile durability is the service record of


similar tile used in an environment similar to the one under consideration.

Standards:ThefollowingASTMInternationalstan-dards apply to roof tile.

Clay Roof Tile: ASTM C1167, Standard Specification for Clay Roof Tiles, addresses material characteristics and physical properties and establishes sampling pro-cedures for clay tile. ASTM C1167 contains classifica-tions for three grades of tile based on their resistances to frost action: Grade 1resistance to severe frost action;

Grade 2resistance to moderate frost action; and Grade 3negligible resistance to any frost action. The standard provides the following separate set of tile classifications by profile:TypeIhigh-profiletilestileshavingarise-to-widthratiogreaterthan1:5;TypeIIlow-profiletilestiles having a rise-to-width ratio equal to or less than 1:5; andTypeIIIallothertiles,includingflat.Otherphysi-cal properties addressed in this standard are wet and dry strength, efflorescence, permeability, finish and texture.

NRCA recommends designers specify clay roof tile that complies with ASTM C1167 requirements.


Figure 3-7: Weathering Indexes in the U.S.

Concrete Roof Tile: ASTM C1492, Standard Specifica-tion for Concrete Roof Tile, addresses material charac-teristics and physical properties and establishes sampling procedures for concrete tile intended as a roof covering. ASTM C1492 classifies concrete tile based on profile: TypeIhigh-profiletile,definedastilewitharise-to-widthratiogreaterthan1:5;TypeIImedium-profiletile, defined as tile with a rise greater than 1/2 of an inch and a rise-to-width ratio of less than or equal to 1:5; Type IIIlow-profiletile,definedastilewithariseequaltoorlessthan1/2ofaninch;andTypeIVaccessorytilesuch as ridge, rake, hip and valley tile used in conjunc-tionwithTypeI,IIandIIItiles.(Tileclassificationbyprofile provided in ASTM C1492 is different from the tile classification by profile provided in ASTM C1167.) Otherphysicalpropertiesaddressedinthisstandardaredimensional tolerances, freeze-thaw resistance, transverse strength, permeability and water absorption.

NRCA recommends designers specify concrete roof tile that complies with ASTM C1492 requirements.

Securement Methods: Many types and combina-tions of securement methods are used for the various types of roof tile. Developments in fastener and attach-ment technology have affected tile securement methods. The roof deck type, underlayment type and attachment, and tile profile should be considered when choosing an attachment method. To select a method of securement or attachment, many conditions need to be considered: wind, deck type, seismic considerations, slope, building codes, local practices and manufacturer recommenda-tions. Fasteners should be made of a corrosion-resistant metal that will remain serviceable in the intended envi-ronment for the roof systems design life.

Roof tile commonly is secured using the following means and methods:

Nails

Screws

Wiretiesandstraps

Clips

Lug-hungapplication

Adhesive-setapplication

Nail Application: Nailing is the most common method offasteningtile.Inhigh-windandseismicareas,morestringent nailing schedules may be required. Designers should consult local code requirements. There are a wide variety of corrosion-resistant metal nail types that have different mechanical and physical properties depending on the metal, nail shape and size, shank type, head type and point type.

Nails should be round-head, sharp-point, 11-gauge (0.12-inch), hot-dipped galvanized, stainless-steel, copper or bronze roofing nails. Nail heads should be low-profile, smooth and flat. Shanks may be smooth, barbed or other-wise deformed for added pull-out resistance. Nails should comply with ASTM F1667, Specification for Driven Fasteners,Nails,SpikesandStaples,TypeI,Style20.NotallnailsthatcomplywithASTMF1667,TypeI,Style 20 have the head dimensions or shank profiles that NRCA recommends.

Nails used to fasten tiles should be long enough to pen-etrate all layers of roofing materials and achieve secure anchorage into a wood roof deck or battens. Nails should extend a minimum of 1/8 of an inch through the under-side of plywood or other acceptable wood panel decks less than 3/4 of an inch thick. For wood plank, wood boards or wood battens, nails should penetrate at least 3/4 of an inch. Tile nails should be driven so the nail head just touches the surface of a tile and the tile hangs on the nail.

Ifpressure-preservative-treatedwoodisencountered,stainless-steel or hot-dipped galvanized-steel fasteners should be used. Pressure-preservative treatment other than chromated copper arsenate (CCA) necessitates that hot-dipped galvanized nails should meet ASTM A153, Standard Specification for Zinc Coating (Hot-Dip) on IronandSteelHardware,ClassDandstainless-steel fasteners should be Type 304 or Type 316.

Screw Application: Some tile roof systems specifically callforattachmentwithscrews.Itmayalsobeanoptionfor other tile roof systems installed over nailable decks or battens. Tile roof systems that accommodate nail and screw fasteners may have different fastening requirements for each fastener type. Designers should consult specific manufacturers recommendations for tile roof system fastening schedules using screws.


Screw fasteners for tile roof systems should be a mini-mum #8 corrosion-resistant and long enough to extend through the underside of plywood decks a minimum of 1/8 of an inch, as well as penetrate a minimum of 3/4 of an inch into wood board or plank decks or battens. Screw fasteners should be compatible with batten material. For galvanized screws, the corrosion-resistant coating should meet the requirements of ASTM B695, Stan-dard Specification for Coatings of Zinc Mechanically DepositedonIronandSteel,Class55.Additionally,itis recommended that corrosion-resistant screw fasteners be performance-rated according to ASTM B117, Stan-dardPracticeforOperatingSaltSpray(Fog)Apparatus.Designers should consult fastener manufacturers for sup-porting information.

Ifpressure-preservative-treatedwoodsubstrateisused,stainless-steel screw fasteners of Type 306 or Type 316 are recommended.

Wire-tied and Strapping Application: Hanging tile with wire often is used as an attachment method on non-nailable or insulated decks or in areas where fasten-ing through metal flashings needs to be avoided. For non-nailable roof decks, a variety of wire and strapping systems are available. Wire tying tile also is specified where penetrating the underlayment is undesirable, such asonlow-slopeapplications.Insomeseismicregions,wire tying tile can be an effective securement method. Nails, screws and expanding fasteners commonly are used in conjunction with wire-tied systems to affix the wire to certain substrates.

Clip Application: Clips sometimes are used in conjunc-tion with other attachment methods in high-wind and seismic areas. Some tile clips commonly are referred to as wind clips or storm anchors. Clips used with the tile courses near an eave may provide increased wind-uplift resistance and may be required depending on the tile system and design parameters.

Lug-hung Application: Many types of tile have lugs formed on their undersides near their heads that may be hungoverthebatten.Insomeareas,whentilesareloose-laid on roofs with low slopes, the tiles are simply hung over the battens. Lug hanging tile usually is used in combina-tion with other securement methods, and some building codes and manufacturers require a specific attachment

pattern for perimeter and field tile depending on a roofs slope and the wind region in which a building is located.

Designers can consult tile manufacturers installation in-structions for additional information regarding lug-hung tile systems.

Adhesive-set Application: Laying tile in a bed of mortar, foam adhesive or other code-approved adhesive is com-mon in some areas of North America where freeze-thaw conditions are normally not encountered.

Tile can be set in mortar, foam adhesive specifically for-mulated for tile application or other approved adhesive applied to a weatherproof membrane such as two layers of underlayment adhered together. Tile application should follow system-specific instructions because manufacturers published uplift resistance values for tile mortar or adhe-sive are associated with specific placement and contact area requirements. Additional tile fasteners are typically required for mortar- or adhesive-set tile systems on roof slopes greater than 6:12.

Designers must also consider the compatibility of the underlayment sheet surface when specifying mortar or adhesive fastening systems. The underlayment system must be attached appropriately to carry the load through to the deck and to meet the uplift requirements of the ap-plicable building code. Roof deck slope, substrate thick-ness, base-sheet tear resistance and fastener/cap type are important design considerations. Underlayment fastening schedules for uplift resistance are determined from fasten-er pullout resistance values and pullover resistance values for underlayment over fastener head or cap.

Model building codes currently do not contain prescrip-tive requirements for approval of mortar- or adhesive-set tile. The basis for code acceptance of these systems by the authority having jurisdiction is found in the applicable codes alternative acceptance provisions. Some mortar and adhesive attachment system manufacturers possess evaluationreportsbyICCEvaluationService(ICC-ES)that may be used to substantiate code compliance to the codeauthorityhavingjurisdiction.Evaluationproto-cols that establish guidelines for code acceptance of tile adhesives under the alternative approval provisions are publishedbyICC-ESasAC152,AcceptanceCriteriaforAdhesive Attachment of Concrete or Clay Roofing Tiles.



Tile mortar or tile adhesive is often used in combina-tion with other securement methods. Tile mechanically fastened at hips and ridges, along eaves, rakes and valleys, and at some other flashing locations are sometimes set in mortar or other approved adhesive. Not all tiles are de-signed for application with mortar or tile adhesive.

Designers can consult tile manufacturers for additional information regarding adhesive-set tile systems.

Asphalt Roof Cement: Roof cements commonly are used in the application of tile roof systems. The base material used in the manufacture of roof cement is either an air-blown asphalt or a polymer-modified asphalt. The asphalt is thinned, or cut back, with a petroleum-based solvent to create a soft, workable mixture. Some roof ce-ments contain mineral fibers as stabilizers. Some manu-facturers now are offering polymer-modified bitumen roof cements.

There are two common types of asphalt roof cement: flashing cement and lap cement. Flashing cements com-monly are used on vertical surfaces and have a trowelable consistency. Lap cements are used more specifically for bonding asphaltic materials together, and their consisten-cies are characterized as either trowelable or brushable.

Asphalt roof cements also are available in different grades. The two most common grades are referred to as winter grade and summer grade. The primary difference between winter grade and summer grade is their softening point temperatures; winter grade has a lower softening point temperature than summer grade.

Common uses for asphalt roof cement in tile roof systems are:

Asabeddingcementforsealingthebaseorflange of a metal accessory to a roof system

Toprovideatemporarysealaroundroofpen-etrations or at walls prior to installing flashing components

Tosealsometypesofhip/ridgeunits

ThefollowingASTMInternationalstandardsareappli-cable to asphalt roof cement used as a utility cement or flashing cement:

ASTMD2822,StandardSpecificationfor

Asphalt Roof Cement, addresses composition, pliability, high-heat behavior and adhesion properties, as well as other physical require-ments.TypeIisacementcomposedofalow-softeningpointasphalt,andTypeIIiscom-posed of a high-softening point asphalt. These classifications are categorized further by the intendedapplication:ClassIisfordrysurfacesandClassIIisfordamp,wetsurfaces.

ASTMD4586,StandardSpecificationforAs-phalt Roof Cement, Asbestos Free, addresses composition, pliability and high-heat behavior, as well as other physical requirements. The ma-terial classifications are the same as in ASTM D2822.

ThefollowingASTMInternationalstandardisapplicableto asphalt roof cement used as a lap cement:

ASTMD3019,StandardSpecificationforLap Cement Used with Asphalt Roll Roof-ing, Non-fibered, Asbestos-fibered, and Non-asbestos-fibered, provides a classification for threetypesoflapcement:TypeIbrushingconsistency with no stabilizers, categorized as Grade 1made with an air-blown asphalt or Grade 2made with a vacuum-reduced or steam-refinedasphalt;TypeIIheavybrushingor light troweling consistency with a quantity ofshort-fiberedasbestosstabilizers;TypeIIIheavy brushing or light troweling consistency with non-asbestos stabilizers.

Elastomeric Flashing Sealant: Certain elasto-meric sealant products may be used in the construction of clay and concrete roof systems as a cement for sealing the base or flange of a metal accessory to a roof or to pro-vide a temporary seal around roof penetrations or at walls prior to installing flashing components.

Elastomericsealantformulationsprimarilyarecharacter-ized as single-component and multi-component. A single-component material is a uniform mixture suitable for direct application; it cures in place, typically as a result of reaction with ambient moisture. A multi-component mate-rial is supplied as two or more separate components requir-ing thorough mixing before it is ready for application; it cures as a result of reactions between the components.


Elastomericsealantmaterialsalsoarecharacterizedaspourable or self-leveling and nonsag or gunnable. Self-leveling materials are intended for application to horizon-tal surfaces. Nonsag materials are intended for applica-tionsonslopedandverticalsurfaces.Elastomericsealantmaterials may further be classified on the basis of their ability to withstand cyclic dimensional changes and their end-use application or substrate type.

ASTMC920,StandardSpecificationforElastomericJoint Sealants, applies to elastomeric flashing sealant. The standard provides a material classification by type, grade, class and use. Single-component materials are clas-sified as Type S. Multi-component materials are classified as Type M. Grade P classification applies to materials that are pourable or self-leveling at 40 F. Grade NS classifica-tion applies to materials that are nonsagging when applied to joints on vertical surfaces between 40 F and 122 F. The classification by class is based on a materials capability to maintain adhesive and cohesive strength when subjected to cyclic dimensional changes. The classification by use is based on satisfactory performance in specific end-use ap-plications and/or on designated substrates.

NRCA recommends elastomeric flashing sealant materials used in clay and concrete roof systems meet the require-ments of ASTM C920, Type S, Grade NS.

Weatherproof Flashing Membrane: Mem-brane materials may be used to weatherproof joints in hip and ridge details in clay and concrete tile roof systems. Membrane materials commonly used in these applica-tions are polymer-modified bitumen sheets, self-adhering polymer-modified bitumen sheets and ethylene-propyl-ene-dieneterpolymer(EPDM)sheets.

Section 2.1Underlayment Materials provides detailed information about polymer-modified bitumen sheets and self-adhering polymer-modified bitumen sheets.

Section 4.4Single-ply Roof Membranes of The NRCA Roofing Manual: Membrane Roof Systems provides de-tailedinformationaboutEPDMsheets.

3.2 Clay and Concrete Tile Roof System Design and Installation

Exposure and Appearance: Clay and concrete roof tile system course spacing (exposure) is determined

by roof tile product design. Generally, a minimum 3-inch course-to-course overlap is recommended, except for plain (flat-slab or shingle) tile, which is installed shingle-fashion and requires a minimum 3-inch head lap. The course-to-course minimum overlap requirement may be reduced to a minimum of 2 inches for clay and concrete tile applied on very steep slopes. Manufacturers should be consulted for product-specific requirements.

Course-to-course joint spacing also is determined by roof tileproductdesign.InterlockingtileandS-tilemaybedesigned with channels or lugs that fix the joint spacing when tiles are set in place or a manufacturer may provide a specific or minimum joint spacing requirement. Pan and cover tile roof systems may provide for fixed-size side laps between covers and pans or a range of side-lap spacings, depending on design and/or desired finished ap-pearance. With plain noninterlocking tile, joint spacing between courses typically equals approximately half the tile width to achieve the desired symmetrical field pattern. Where a plain noninterlocking roof tile system intention-ally is installed to achieve an asymmetrical field pattern, the minimum joint spacing between adjacent courses should not be less than 3 inches.

Starter Course: Plain (shingle) tile systems are start-ed similarly to slate and wood shakes. A starter course is laid; a first course is laid with appropriate side joint offset; and succeeding courses are laid with designated exposure to achieve the necessary head lap. Single-layer tile systems are laid with aligned or offset side joints as recommended by the manufacturer. The recommended overlap is des-ignated by the manufacturer to achieve the selected field pattern.

Eave Cants: With most interlocking and plain tile roof systems, an eave cant or other elevation method is secured to a roof deck along the eave to establish a uni-formslopeangleforalltilecourses.Insomeapplications,fascia boards are raised to elevate the first tile course and establish the slope for the remaining courses in lieu of an eave cant. A tapered or sloped elevation strip should be used to support the underlayment along the downslope perimeter. See Figure 3-8 on page 136. Where eave cants or raised fascia boards, or both, are used as means to es-tablish the slope for tiles, they should be designed and installed to provide positive drainage to eave edges.


Eave Closures: Eaveclosuresareusedwithsometile types and profiles and help close off the open space at roof perimeter edge between tile and underlying con-struction and raise the first tile course to a slope angle matching that of upslope tile courses. Clay, cement, mortar, pressure-sensitive adhesive membrane, foam and specialty metal closures are often used with tile. Closures help keep birds from nesting in the open ends of the first tilecourse.Eaveclosuresshouldbedesignedandinstalledto allow unobstructed drainage of water that may collect on the underlayment. Accessory closures may have weep holes to allow water drainage and eliminate damming at eaves. See Figure 3-9.

Hips and Ridges: To weatherproof a roof at hips and ridges, special hip and ridge trim tiles are used as hip and ridge coverings. Also, accessory closures similar to eave closures may be installed at ridges and hips.

When installing hip and ridge tiles, underlayment should be wrapped and nailed over the hip and ridge nailer ex-cept at venting ridges where underlayment would close ventilation space. A wood nailer or hip and ridge stringer commonly is installed to a roof deck at hips and ridges to provide a substrate for secure anchorage of hip and ridge tiles.Incombinationwithmechanicalfastening,hipandridge tile can be set in mortar, foam or other approved material. See Figure 3-10.

Rakes: To weatherproof a tile roof system along rake edges, specific details used depend on the tile type and profile, climate, and regional or area practices. Most tile roof systems use specialty tile at the rakes though rake

edge metal flashing also may be used. With plain tile, rake tile or perimeter metal flashings usually arent used. A plain tile roofs rake edge may be detailed similar to the rake edge of a slate roof where the perimeter tiles are ex-tended beyond the rake edge to provide a water-shedding drip edge for runoff and help provide some weather pro- tectionfortheunderlyingbuildingcomponents.Exam-ples of rake edge treatments are depicted in Figures 3-11 and 3-12.

Drip Edge Metal: Depending on the severity of the climate, anticipated rainfall, freeze-thaw cycling, edge framing construction and the use of preformed perimeter edge tile, the use of drip edge metal should be considered. The installation of drip edge metal at eaves and rakes of a tile roof system is an option for a clean termination of underlayment.Italsoprovidesforeffectivewater-shedding.

RAISED FASCIA BOARD

BEVELED WOOD CANT OR ELEVATING MATERIAL

Figure 3-8: Cant or elevation strip that may be used with raised fascia

CLAY CLOSUREWITH WEEP HOLES

FIELD TILE

SLOP

E

Figure 3-9: Downslope clay closure

MORTAR BED ORAPPROVED ADHESIVE

FASTENERS

PAN AND COVER FIELD TILE

RIDGE FASTENERS

NAILER

Figure 3-10: Tile ridge covering


Where climate or roof edge construction dictates the need for drip edge metal, the type and minimum thickness of the metal should be commensurate with the expected service life of the tile roof system. NRCA recommends corrosion-resistant metal be specified for drip edge metal material.

NRCA suggests fastening drip edge metal at about 12 inches on center, slightly staggered. Spacing may need to be closer in high-wind regions.

NRCA recommends drip edge metal for tile roof systems be fabricated from one of the following metal types and minimum thicknesses:

24-gaugeprefinishedgalvanizedsteel

26-gaugestainlesssteel

0.0216-inch-thickcopper-coatedstainlesssteel

0.032-inch-thickprefinishedaluminum

16-ouncecopper

16-ouncelead-coatedcopper

Valleys: A valley is created at the downslope intersec-tion of two sloping roof planes. Water runoff from the portions of roof areas sloping into a valley flows toward and along the valley. Because of the volume of water and the lower slope along a valley line, such an area is espe-cially vulnerable to leakage. A clear, unobstructed drain-age path is desired in valleys so the valley can carry water away quickly and perform successfully for the service life of the roof system.

Where roofs of two equal slopes join to form a valley, the slope of the valley is less than that of the two adjacent fields of the roof. For example, where two sloped roofs with slopes of 4:12 intersect at a valley, the actual valley slope is only about 3:12.

With tile roof systems, there are two basic types of valleys:

Openvalleys

Closedvalleys

These two general types of valleys are constructed only after the necessary layer(s) of underlayment and any valley-lining material specified have been applied to a deck.

Valley underlayment construction consists of an additional full-width sheet of a polymer-modified bitumen under-layment, base sheet, or self-adhering polymer-modified bitumen sheet. This valley underlayment is centered in a valley. Mechanically attached valley underlayment sheets are secured with only enough fasteners to hold them in place until the balance of valley materials is applied. The courses of underlayment from the fields of two adjoining

Figure 3-11: Interlocking tile rake detail with rake tile

APPROX. 1 OVERHANG AT RAKE END

OVERHANG AT DOWNSLOPE EDGE

APPROX. 1

Figure 3-12: Plain tile rake detail with tile extended beyond roof perimeters to create a drip edge


roof areas are extended so each course overlaps the val-ley underlayment by at least 12 inches. A valley is then lined with the balance of the valley flashing. Another recognized installation method is weaving intersecting underlayment courses through a valley in addition to the sheet centered in the valley on top of the underlayment. All layers of underlayment in and through a valley should be tight with no bridging.

To prevent leakage, it is important with all types of valley construction to avoid placing fasteners and penetrations near the center of a valley. Generally, fasteners should be kept back from the center of a valley a minimum of 8 inches. However, with very shallow valleys or in climates where freeze-thaw cycling or intense rainfall may be regu-larly anticipated, holding nails back farther from the cen-ter of the valley is not uncommon.

Open Valleys: An open valley is constructed by installing typically 8-foot or 10-foot lengths of corrosion-resistant metal from the low point to high point in the valley. The tiles and, in some regions, underlayment are lapped on both sides of the valley metal, leaving a clear space be-tween the roofing material to channel runoff water down the valley. See Figure 3-13.

The type and minimum thickness of the metal used in an open valley should be commensurate with the expected service life of the tile roof system. NRCA suggests valley metal for tile roof systems be fabricated from one of the following metal types and minimum thicknesses:




0.040-inchprefinishedaluminum

20-ouncecopper


4-poundlead

Insomeregions,particularlythosewithmildclimates,other types of metal and/or metals of lesser thicknesses than listed above may be used successfully.

NRCA also suggests valley metal be formed into a W shape with a splash divider or rib in the center. A center rib can be especially beneficial in valleys where adjoining roof areas have unequal slope because the rib helps pre-vent wash over of runoff. A center rib should not be less than 1 inch high. For easier installation and for control-ling thermal expansion and contraction, NRCA suggests valley metal pieces used with tile roofing be no longer than 10 feet.

NRCA recognizes that V-shaped valley metal performs satisfactorily in certain environments but not when a valley is formed by two different roof slopes.

For numerous types and profiles of tile, optional valley metalprofileshaveevolved.Oneoptionalvalleymetalprofile is the open-throat or double-crown valley that is formed with two major ribs. Another optional valley metal profile is the triple-crown valley, formed with three ribsa minor rib on each side of the major center rib; see Figure 3-14. These profiles can be beneficial in help-ing hold the nose lug or butt end of tile that has been trimmed to fit along a valley.

NRCA recommends valley metal for use with clay and concrete tile be a minimum of 24 inches wide. This means the flanges on each side of a metal valley centerline are about 11 inches wide.

With plain tiles, the irregularities of the metal valley clips and hemmed valley flange edges may not allow the roof covering at the valley to lie smoothly. This unevenness of the tile lying over the clips and hemmed edges can impede drainage. Therefore, in some regions of North America, metal valleys are secured by simply nailing along

Figure 3-13: Open valley using metal valley flashing


bothoutervalleymetalflanges.Inregionswheresnowand ice typically occur, the outer flanges may then be stripped in with self-adhering polymer-modified bitumen sheet.

Openvalleyspermitclear,unobstructeddrainageandareadvantageous in locations where foliage shed from sur-rounding trees settles on a roof surface and tends to accu-mulate in the valleys where slopes are relatively shallow.

Inclimatespronetoaccumulationsofsnowandiceorwith regular freeze-thaw cycling, open valley construction can be enhanced by the following procedures:

Liningthevalleywithaself-adheringpolymer-modified bitumen underlayment material before application of the metal valley

Strippinginflangesoneachsideofthemetalvalley with a 9-inch to 12-inch strip of self-adhering polymer-modified bitumen underlay-ment material. The self-adhering material is adhered onto the valley metal flange and the underlying width of similar self-adhering underlayment material.

Attachingvalleyflashingmetalwithclipsratherthan through-fastening

AddingaclosureattheeaveoftheW-shapedvalley metal to minimize water and ice infiltration

Taperingthevalleysoitiswideratitslowpointthan its high point

Tapering the valley has the following advantages:

Itallowsforincreaseinwaterrunoffvolumetobe received at the downslope end.

Itallowsanyicethatmayformwithinthevalleyto free itself when melting and slide down and exit the valley rather than lodging somewhere along the length of the valley.

A valleys width, or the amount of space between valley tiles from the adjacent roof areas, should increase uni-formly so the valley widens as it continues downslope. The difference in the width of the upper end of a valley andlowerendisreferredtoasthetaper.Inmostclimates,the amount of valley taper is suggested to be about 1/8 of an inch per foot of valley length. For example, in a valley

Figure 3-14: Valley metal profiles


that is 16 feet long, the distance between tiles should be 2 inches greater at the bottom of the valley than at the top. The length of a valley may necessitate a wider metal pro-file to allow for taper from top to eave.

Closed Valleys:Inaclosedvalley,tilesonbothsidesarecut at an angle parallel to the centerline of the valley and butted together to form a mitered joint. Valley metal similar to the metal valley lining used with open valleys also is used in closed valley construction since water flows through tile joints in the valley. See Figure 3-15. Closed valley construction with mitered joints is appropriate for plain and flat interlocking tile. The roof areas intersecting at a closed valley should be of the same slope so that cor-responding tile courses from either side of the valley align at the mitered joint in the center.

Inareaswhereheavyaccumulationsoffoliageshedfromsurrounding trees are expected or if moss can be expected to grow in tile roofing joints, a closed valley can hamper water runoff. Therefore, specifying a closed valley should be carefully considered to be sure it is appropriate for a particular project.

Itisimportantinallvalleyconstructiontypestoavoidplacing fasteners near the center of a valley to prevent leak-age. Generally, fasteners should be kept back from the cen-ter of a valley by a minimum of 8 inches. Where double- or triple-crown valley metal is used, fasteners must not be placed inside valley metal diverter ribs. To avoid fasten-ing too close to the center of a valley, tile may be secured with adhesives or wire-tied attachments. Wire-tied attach-ment methods may be used with closed and open valleys.

Flat and plain interlocking tile closed valleys also may be formed by laying tile tight against the valley line with mi-tered joints and placing individual pieces of metal flash-ing under each tile course along the valley centerline simi-lar to step flashing treatment. Step valley flashing metal length should match the tile length and may be hemmed and fastened with cleats or fasteners placed along the edges.

Flashings: Because roof systems are frequently inter-rupted by the intersection of adjoining roof sections, ad-jacent walls, or penetrations such as chimneys, curbs and vent pipe stacksall of which create opportunities for leakagespecial provisions for weather protection must be made at these locations. Careful attention to flashing details is essential to successful long-term roof system

performance, regardless of the type of roof construction. NRCA suggests the use of self-adhering underlayment material at various flashing and termination details such as chimneys, walls, rakes, eaves, valleys, pipes, vents, curbs and kick-outs.

Flashings are divided into the following categories:

Penetrationflashings

Verticalsurfaceflashings

Skylightflashings

Steep-tolow-slopetransitions

The type and minimum thickness of the metal used for metal flashings should be commensurate with the expected service life of the clay tile or concrete tile roof system. NRCA suggests metal flashings used in clay tile or concrete tile roof systems be fabricated from one of the following metal types and minimum thicknesses:




0.040-inch-thickprefinishedaluminum

20-ouncecopper

VALLEY METAL

WIRE TIE

STRIPPING PLY

Figure 3-15: Closed valley using valley metal



4-poundlead

Insomeregions,particularlythosewithmildclimates,other types of metal and/or metals of lesser thicknesses than are listed may be used successfully.

Penetration Flashings: There are many small penetra-tions that need to be flashed into tile roof systems, such as vent pipe penetrations, exhaust vents, exhaust fans, furnace or water heater flue pipes, electrical standpipes and others. This is typically accomplished with the use of some type of flat flange that extends around a penetration and is installed under the tile and underlayment on the upslope side of the penetration and extends down on top of the tile at the downslope side. Attached and sealed to the flange is a cylinder or a rectangular box used to seal around a penetration. The flange can be set into asphalt roof cement of elastomeric flashing sealant for additional protection. The flange of a flashing used for tile with a curved surface is fabricated from a soft metal that can be formed to follow the surface contours. These flashing components are often supplied by other trades but may be installed by a roofing contractor. See Figure 3-16.

Another method is to install a primary metal flashing under the underlayment at the upslope side of a penetra-tion and over the underlayment on the downslope side. A secondary flashing is installed at the tile level where the upslope side of the flashing is under the tile and the downslope side of the flashing extends over the tile.

Vertical Surface Flashings: Flashings at a vertical surface-to-roof plane intersection should have a relatively smooth substrate on the roof plane and vertical plane, up to a sufficient height, to receive the metal flashing. Rough or contoured vertical surfaces, such as cut stone and rough timber, should be provided with a flush substrate above the roof line configured to accept the vertical flashing and/or counterflashing or it may be possible to use soft-metal flashings formed to follow the substrates contours.

Four types of metal flashings are commonly used at loca-tions where a tile roof system intersects a vertical surface: apron flashing, channel flashing or step flashing, cricket or backer flashing, and counterflashing. See Figure 3-17.

Generally, before flashings are applied, a layer of self-adhering polymer-modified bitumen sheet or other

appropriate underlayment should be applied to a roof deck around roof penetrations. Self-adhering membrane underlayment may be installed to a roof deck at the base of walls and around chimneys or curbs. A self-adhering water and ice-dam protection membrane can assist in keeping water from migrating into a roof system at these roof-to-wall intersections during times of severe winter freeze-thaw cycling.

Figure 3-16: Various types of penetration flashings

CRICKET OR BACKER FLASHING

COUNTERFLASHING

APRON FLASHING

CHANNEL FLASHING

Figure 3-17: Sheet-metal flashing components used at a chimney


Apron Flashing: Apron flashings provide a weatherproof-ing transition material where a roof area intersects a head wall. Common locations for apron flashings are the front or downslope side of a dormer, chimney or curbed roof penetration, and other horizontal-to-vertical transitions. Figures 3-18 and 3-19 show an apron flashing used at the front side of a chimney.

Channel Flashing or Step Flashing: For tile roof systems where a roof area intersects a vertical side wall, a channel flashing or step flashing is installed. Channel flashings also are referred to as pan flashings. Unlike a step flash-ing, a channel flashing is installed so it extends under tile along the length of a wall rather than being interwoven between tile courses. A channel flashing should direct water away from the wall and past the eave or on top of a downslope flashing or tile.

Stepflashingmethodisappropriateforplaintile.Indi-vidual metal step flashing units are installed at the end

of each course of flat or plain tile. Channel flashings are appropriate for medium- and high-profile tile.

Common locations for channel flashings or step flash-ings are the sides of chimneys, dormers and curbed roof penetrations. Figure 3-20 shows step flashings used with plain tile at a chimney.

Figure 3-21 shows channel flashing used with pan and cover tile at a chimney.

Figure 3-22 shows channel flashing at a vertical wall.

When using plain tile, a step flashings length generally is the length of the tile. Step flashing should be made from a durable material and heavy enough gauge to last as long as the tiles expected service life. For most climatic regions, NRCA suggests using metal step flashing pieces sized such that they match the tile in length so a mini-mum step flashing head lap is achieved. The step flashing width should be sufficient to obtain a 4-inch extension

Figure 3-18: Apron flashing at masonry chimney for pan and cover tile

Figure 3-19: Apron flashing at masonry chimney for interlocking or plain tile

STEP FLASHING EXTENDING 4" MIN. UP WALL

STEP FLASHING

NOTE:COUNTERFLASHING NOT SHOWN FOR CLARITY

Figure 3-20: Step flashing at a masonry chimney for plain tile

CHANNEL FLASHING EXTENDING4 MIN. UP WALL

NOTE:COUNTERFLASHING NOT SHOWN FOR CLARITY

EXTENDCHANNELFLASHING TO BOTTOMCORNER OFWALL

NAILER

Figure 3-21: Channel flashing at a masonry chimney with pan and cover tile


onto each underlying tile and about a 4-inch vertical height over the exposed face of each overlying tile.

Special attention needs to be paid to the bottommost step flashing and the downslope end of a channel flashing where an eave intersects a continuous wall to ensure water is diverted to the outside of the wall covering. NRCA rec-ommends a kick-out at this intersection. See Figure 3-23 for examples of kick-out flashings.

Cricket or Backer Flashing: When a roof area intersects an upslope side of a chimney or curbed roof penetration, either a cricket or backer flashing is installed. A cricket diverts water around a penetration, and a backer flashing provides a weatherproofing transition material where a roof intersects the back side of a penetration.

Backer flashing is generally limited to penetrations that are 24 inches wide or less. See Figure 3-24.

NRCA recommends designers specify crickets at the upslope side of chimneys or curbed roof penetrations when the chimney or curb is more than 24 inches wide.

Figure 3-22: Channel flashing at a vertical wall

Figure 3-24: Sheet-metal backer flashing at a chimney

Figure 3-23: Examples of kick-out flashings


A backer flashing or deck flange of a cricket flashing should have hemmed edges and should extend upslope under tile a minimum distance equal to three times the tile exposure. Underlayment should overlap the upslope edge of the flashing.

For all metal crickets, NRCA suggests wood framing and decking be installed beneath crickets to support them. Figures 3-25 and 3-26 illustrate examples of crickets used behind chimneys.

Counterflashing: Apron, step or channel flashings and cricket or backer flashings require some form of coun-terflashing to cover and protect their top edges from waterintrusion.Inmanyinstances,thewallcoveringorcladding material performs the counterflashing function. When this does not occur, a metal counterflashing that is mounted to a vertical wall should be installed along the top edge of the flashing metal. See Figure 3-27.

The counterflashing material should be compatible with

the cladding and substrate (e.g., aluminum and masonry should not be in direct contact).

Where wall cladding counterflashes wall flashing metal (e.g., step flashing), NRCA recommends cladding material and the water-resistive barrier extend past and cover the top edge of the flashing metal a minimum of 2 inches.

For additional information regarding counterflashing, refer to the Architectural Metal Flashing section of The NRCA Manual: Architectural Metal Flashing, Condensa-tion Control and Reroofing.

Skylight Flashings: Skylights, in terms of roof flashing, are much the same as other vertical surface flashings, particularly chimney flashings. Skylight flashings gener-ally consist of an apron flashing, channel or step flashing, andcricketorbackerflashing.Inmostinstances,theskylight unit itself functions as the counterflashing. Refer to AppendixRoof Accessories for detailed information regarding skylights.

Steep- to Low-slope Transitions: Sometimes, tile roof systems terminate and drain onto adjacent membrane roofsystems.Inthesesituations,atileroofsystemalsoserves as the counterflashing for the membrane roof system.

For steep- to low-slope transitions, NRCA recommends the tile be held back a minimum of 10 inches above the transition. See Figure 3-28.

APPROX. 1"

SEALANT

INSERT COUNTERFLASHING WITH UNDERBROKEN TOP HEM FOR

FRICTION FIT

OPTIONAL: SOFT METAL WEDGE

Figure 3-27: Metal counterflashing inset in masonry mortar joint

Figure 3-25: Wood cricket built on upslope side of chimney

Figure 3-26: Cricket flashing for upslope side of masonry chimney


Specific guidance regarding properly terminating a membrane roof system is provided in Chapter 10 Construction Details of The NRCA Roofing Manual: Membrane Roof Systems.

Figure 3-28: Steep- to low-slope transition

clay tiles

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