Our page top photo shows clay roofing tiles installed in the Northeastern United States, on a combination steep and low slope roof. The metal tabs exposed at the lower edge of many of these tiles indicates that the roof has had extensive repair work.
Carson Dunlop's sketch (left) illustrates typical methods of securing clay tiles to the roof deck.
Fasteners for clay tile roofs: clay tiles are secured to the roof deck using wire, special clips, concrete, ballast stones, or metal clips. Tiles are secured loosely - overly-tight wires or nails are likely to break the tile.
Also used to secure clay tiles on some roofs are aluminum nails, hot dipped galvanized steel nails, or stainless steel nails.
Clay tiles at roof gable edges are often nailed through multiple pre-cast holes in special roof edge tiles in areas where wind blow-off is a common risk.
The fastener schedule for clay roofing tiles varies by geographic area, as we discuss below.
Where nails are used, one or two nails per clay tile is usual. In some jurisdictions (areas of low storm and wind damage risk) only every third or fourth course of tiles is nailed, and in the roof shown in our photo (below right) none of the tiles was secured except those at the roof edges where mortar was applied.
The clay tile roof battens shown in the sketch ( left) are discussed at CLAY TILE ROOF BATTENS & STACKING. Our photo (above right) illustrates a clay tile roof undergoing repair in San Miguel de Allende, Mexico.
This tile roof is in a sheltered location and as is local custom, the clay roofing tiles are barely secured, perhaps only at the roof edges where tiles are set in cement.
At above right Carson Dunlop's sketch illustrates how the eaves are closed at the lower roof edges where a clay tile roof is installed.
The preferred method of attachment depends on the type
of tile, climate conditions, and slope of the roof.
Loose Laid Clay Tile Roofs
For standard concrete tiles with lugs set on
battens, building codes still allow tiles to be laid loose at
slopes less than 5:12 (except for one nail per tile within
36 inches of hips, ridges, eaves, or rakes). Loose-laid tiles
are not allowed, however, in snow regions, areas subject
to high winds, or with tiles weighing less than 9 pounds
per square foot installed.
Selection of Nails Used on Clay Tile Roofs
Nails are the least expensive and most common
method for attaching concrete and clay tiles. Tiles can be
nailed either directly into the roof sheathing or tiles with
lugs can be nailed to battens. Corrosion-resistant nails must
be minimum 11 gauge, with 5/16 -inch heads, and long enough
to penetrate the sheathing by
3/4 inch—typically 8d nails.
Photo at left: a clay tile "gravity" roof sheltering a grave marker in Rodriguez, Guanajuato, Mexico. Gravity-alone clay tile roof installations are common and are somewhat successful only in inland areas not subject to high winds or other severe weather conditions.
Ring-shank nails or hot-dipped galvanized nails hold better
than smooth-shank nails in areas subject to heavy winds.
Whether driven by hand or pneumatic nailers, nails should
be driven so heads lightly touch the tile but not so tight as
to risk cracking tiles.
Because of the longevity of a tile roof,
some contractors use copper or stainless-steel roofing nails.
No. 8 or 9 stainless-steel or brass screws also work well
and are sometimes used in high-wind regions.
Most tiles have two prepunched nail holes. On curved
tiles, use the hole closest to the deck surface unless a nail
there would penetrate a critical flashing.
The other hole is
also used for cut tiles or applications requiring two nails.
For example, all flat, non interlocking tiles require two
nails. And in snow regions, codes require two nails per tile
for all types and slopes.
Otherwise follow the guidelines
in Table 2-9 above or the manufacturer’s guidelines if they are
In the 1990's NRCA's Thomas Smith noted that a paper published in the Proceedings of the 10th Conference on Roofing Technology expressed concern for the lack of conservative roofing industry guidelines for the components of tile roofing systems in the U.S.
Photo at left: steep clay tile roof on a Boston MA cathedral.
The recommendations in the then-current NRCA Steep Roofing and Waterproofing Manual indeed included recommendations for tile roof underlayment, fasteners, and metal flashings, but Smith noted that these were "non-conservative" for many areas in the United States (and other locations of challenging weather).
Smith posed some interim fastener options to improve the life of tile roof systems, including
Copper, grass, or stainless-steel nails, clips, or tie-wire fasteners are recommended
In areas that are typically hot and dry, corrosion protection need not be as conservative, and galvanized steel (less costly) was found acceptable
When using galvanized materials, the thickness of the zinc coating was deemed important
When using galvanized nails they should meet ASTM A 6641
When fastening tiles directly to plywood or to OSB roof sheathing use ring or screw shank nails
Note: Bliss's fastener suggestions above incorporate and update this historical data. - Ed.
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Green Roof Construction and Maintenance, Kelley Luckett, McGraw-Hill Professional, 2009, ISBN-10: 007160880X, ISBN-13: 978-0071608800, quoting: Key questions to ask at each stage of the green building process Tested tips and techniques for successful structural design
Construction methods for new and existing buildings
Information on insulation, drainage, detailing, irrigation, and plant selection
Details on optimal soil formulation
Illustrations featuring various stages of construction
Best practices for green roof maintenance
A survey of environmental benefits, including evapo-transpiration, storm-water management, habitat restoration, and improvement of air quality
Tips on the LEED design and certification process
Considerations for assessing return on investment
Color photographs of successfully installed green roofs
Useful checklists, tables, and charts
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Slate Roofs, National Slate Association, 1926, reprinted 1977
by Vermont Structural Slate Co., Inc., Fair Haven, VT 05743, 802-265-4933/34. (We recommend this book if you can find it. It
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The Slate Roof Bible, Joseph Jenkins, www.jenkinsslate.com,
143 Forest Lane, PO Box 607, Grove City, PA 16127 - 866-641-7141 (We recommend this book).