Page B2.2 . 13 November 2002                     
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    Basics - Clay Tile Roofing

    continued

    According to ASTM Standard C 1167, there are three grades of resistance to frost: Grade I "Provides resistance to severe frost action"; Grade 2 "Provides resistance to moderate frost action"; and Grade 3 "Provides negligible resistance to any frost action."

    The selection of a tile should reflect an appropriate grade. Some fiber-cement tiles have delaminated in climates with severe freeze-thaw cycles, and most manufacturers will not warrant their products in these areas. The best indication of a roof tile's durability is a service record of similar tile used in a comparable climate.

    The roof installation method should be based on roof slope, type of roof deck or substrate, climate, seismic considerations, local building codes, and manufacturer's recommendations. Methods include lug-hung, bedding in mortar, nails, screws, wire, clips, and adhesives. Nails are the least expensive and most widely used installation system.

    Adhesives outperform mortar bedding in hurricane-force winds and are used extensively in southern Florida. They cost the same as two nails and a hurricane clip, but installation is faster. Adhesives are new on the market so little field knowledge of their durability exists.

    Techniques and Tools for Replacing Tiles

    A preliminary assessment of the condition of a tile roof can be done from the ground with binoculars. Critical areas to assess for missing, cracked, or slipped tiles and missing mortar include the ridge, each horizontal row, valleys, and where the roof changes direction.

    Fasteners and flashings should also be surveyed. Check flashings at valleys, chimneys, dormers, vent pipes, and other roofing protrusions. Check also for the condition of gutters and leaders (on a rainy day for best results). Faulty gutters and leaders will direct water onto roof and wall surfaces that were not designed for high water flows. These areas should be inspected carefully for damage and deterioration.

    Inspect the attic for water stains, rot, or other indications of problems. If there are only a few damaged tiles, and if the roof is less than 100 years old, it is likely that replacement tiles are available and individual tiles can be replaced. This is usually a project for an experienced roofer, especially if the damaged tiles are in the roof's field, because tiles can be easily broken from roof traffic, and the surface is dangerous to walk on.

    The isolated replacement of a few tiles is relatively easy, but for more extensive work, a contractor experienced in the installation and maintenance of tile should be engaged (suppliers of roofing tile can frequently be a good referral source).

    Inexperienced contractors may recommend the removal of a tile roof when, in fact, it is still serviceable. In some instances, even when substantial areas have suffered from neglect, tiles can be removed, flashings and underlayment repaired, and the tiles reinstalled with new tiles placed in areas where they are less visible.

    The advantage of repair over replacement is that although repairs require more skill than other roof materials, they are cost-effective over small areas. In some instances tiles can be removed and reused.

    There are disadvantages in that experienced contractors are required, and costs are difficult to estimate in advance. Repairs over large areas can be very expensive, and existing tile may be difficult to match.

    Installing New Clay Roof Tile

    Because of the long service life of clay tile, it is recommended that a high-performance underlayment be installed. Clay roof tiles come in a variety of colors in both earth tones and glazed primary colors. Unlike some other roofing products, clay roof tiles maintain their color over time.

    Celadon Ceramic Slate produces a clay tile that looks like state and weighs 580 pounds per square (5.8 pounds per square foot, or 28 kilograms per square meter). Costs are a function of tile size and the manufacturer's production volume and processes. Smaller tiles cost more per area to purchase and install than larger tiles.

    There are several advantages of installing new clay tiles. Clay tiles are a traditional roofing material. They come in a variety of types and styles. They are perceived as a high-end, quality construction material; are long lasting and virtually maintenance free; are fireproof and impervious to insects and rot; will withstand hurricane winds better than other roofing products; and many resist the effects of freeze-thaw cycles.

    The disadvantages are that clay roof tiles are more difficult to install than other roofing products. They are not recommended for roofs with less than a 4-in-12 pitch (18-degree angle). They are heavy and can weigh anywhere from 520 to 1,250 pounds per square (25 to 60 kilograms per square meter).

    Additional roof supports may be needed for existing roofs before clay roof tile is installed. Clay roofing tile has a relatively high first cost. Because of the limited number of clay roofing tile manufacturers, the material may have to be shipped long distances, increasing costs dramatically.

    Steven Winter Associates, Inc. is a research and consulting firm with specialized expertise in technologies and procedures that improve the performance and cost effectiveness of buildings. Editor Michael J. Crosbie is editor-in-chief of Faith & Form, an associate with Steven Winter Associates, and a contributing editor to ArchitectureWeek.

    This article is excerpted from Home Rehab Handbook, copyright 2002, available from McGraw-Hill Professional and at Amazon.com.

    Note: the photographs do not appear in the book.

     

    AW

    ArchWeek Image

    The Pantheon in Rome has a clay tile roof.
    Great Buildings Photo Donald Corner and Jenny Young

    ArchWeek Image

    Examples of clay tiles.
    Image: Steven Winter Associates

    ArchWeek Image

    New tiles imported from France for use in Dubrovnik, Croatia.
    Photo: Steven Allan

    ArchWeek Image

    Examples of concrete tiles.
    Image: Steven Winter Associates

    ArchWeek Image

    The Horyu-Ji Temple, at Nara, Japan, built in the year 607.
    Great Buildings Photo Lawrence A. Martin

    ArchWeek Image

    The Home Rehab Handbook.
    Image: McGraw-Hill Professional

     

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