Figure 2-20 Roof Underlayment for Clay Tiles (C) J Wiley, S Bliss Clay Tile Roof Slope, Sheathing, &
Clay Tile Roof Underlayment Specifications

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Clay tile roof slope, sheathing, underlayment specifications: this article describes the requirements & specifications for clay tile roof installation: roof slope, roof sheathing,m and clay tile roof underlayment.

This article series discusses best practices in the selection and installation of residential roofing. This article includes excerpts or adaptations from Best Practices Guide to Residential Construction, by Steven Bliss, courtesy of Wiley & Sons.

Also see our clay roof tile home page CLAY TILE ROOFING and see CLAY TILE ROOF STYLES, DESIGNS for detailed descriptions of different clay roof tile styles and characteristics, and see ROOFING TILE SHAPES & PROFILES for the basics of roof tile profiles and what they mean.

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Tile-Covered Roof Slope Specifications

Table 2-5: Clay tile roof slope requirements (C) J Wiley, S BlissAdapted/paraphrased with permission from Best Practices Guide to Residential Construction, chapter on BEST ROOFING PRACTICES:

Roof Slope Requirements for Tiled Roofs

Most manufacturers recommend minimum slope requirements for their tiles as well as special underlayment and fastening techniques for low-slope installations.

[Click to enlarge any image]

Typical minimums are shown in Table 2-5. Some manufacturers allow specific tile types to be installed on roofs as shallow as 2 1/2 :12 if a full waterproofing layer, such as a built-up roof or single-ply membrane, is installed.

Reduced exposure and special fastening techniques may also be required for low slopes.

On slopes less than 3 1/2 :12, roofing tile is considered decorative only. The underlying roof provides all the necessary waterproofing.

In general, there is no maximum slope for tile roofs. However, on extremely steep roofs above 19:12 or on vertical applications, wind currents may cause tiles to rattle. To avoid this, use wind clips on each tile along with a construction grade silicone sealant or other approved sealant.

More information about roof slope & roof slope calculation or measurement is at ROOF SLOPE DEFINITIONS.

Roof Sheathing Requirements for Tiled Roofs

While spaced sheathing is allowed under the codes, most installations today are done on solid wood sheathing with or without battens. The sheathing must be strong enough to support the required loads between rafters. Minimum requirements are nominal 1 inch for board sheathing or 15/32 for plywood and other approved panel products.

Underlayment Requirements for Clay Tiled Roofs

Figure 2-20 Roof Underlayment for Clay Tiles (C) J Wiley, S Bliss

Because of the long service life of tile, a long-lasting underlayment should be used as well. Underlayments play a key role in tile roofing, since most tile roofs are not completely waterproof.

At a minimum, use a Type II No. 30 or No. 43 felt, lapped 2 inches on horizontal joints and 6 inches at end laps. The underlayment should lap over hips and ridges 12 inches in each direction and turn up vertical surfaces a minimum of 4 inches (Figure 2-20).

At tricky areas, such as around roof vents, chimneys, and skylights, self-adhesive bituminous membrane can help achieve a watertight seal.

In windy areas, use tin caps or round cap nails to hold the underlayment securely. The fastening schedule for the underlayment will depend on local wind conditions.

For harsher conditions or shallower slopes, use mineral surface roll roofing, self-adhering bituminous membrane, or other durable waterproofing systems.

For slopes below 3-1/2:12 the underlayment must provide complete weather protection, and the tiles are considered merely decorative. Underlayment recommendations for different types of tiles and climate conditions are shown in Table 2-6, Table 2-7, and Table 2-8 below. [Click to enlarge any tables or images in these articles.]

Table 2-6 Clay Tile Roof Underlayment Recommendations (C) J Wiley S Bliss Table 2-6 Clay Tile Roof Underlayment Recommendations (C) J Wiley S Bliss Table 2-6 Clay Tile Roof Underlayment Recommendations (C) J Wiley S Bliss

Tile Roof Underlayment Options from NRCA

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.

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 underlayment options to improve the life of tile roof systems, including for 4" in 12" or greater (steeper) sloped tile roofs:

  • A single layer of organic smooth-surfaced roll roofing meeting ASTM D 224 Type I or II (II is preferable)
  • Two layers of coated organic base sheet meeting ASTM D 2626 (un perforated)
  • Two layers of organic felt meeting ATM D226 Type II (30 pound felt) over 1 layer of ASTM D226 Type I (15 pound felt)
  • One layer of self-adhering modified bitumen meeting ASTM D 1970, over one layer of ASTM D226 Type I (15 pound felt) to make it easier to later remove self-adhering underlayment and reducing moisture damage to the deck
  • One layer of self-adhering modified bitumen underlayment meeting ASTM D 1970, under one layer of ADTM D 226 Type II 30 pound felt
  • Certain types of SBS modified bitumen, heavyweight sheets may also be good underlayments, but Smith noted that until ASTM standards were developed, specifying those products was difficult.

Special provisions were needed for lower slope roofs (under 4" in 12")

Roofing Materials, Methods, Standards

  • Asphalt Roofing Manufacturers Association (ARMA)
  • Cedar Shake and Shingle Bureau
  • Metal Roofing Alliance
  • The Tile Roofing Institute, 23607 Highway 99, Suite 2C Edmonds WA 98026 P: 425.778.6162 F: 425.771.9588 Email:, Website: supported by the Western States Roofing Contractors Association. The Tile Roofing Institute publishes the "Concrete and Clay Roof Tile Installation Manual for Moderate Climate Regions, Design Criteria", retrived 5/2/2014, original source: TRI_Moderate_Guide_HIGH_RES.pdf

Where to Buy Concrete Roof Tiles

  • Bartile Roofs
  • Eagle Roofing Products
  • Entegra Roof Tile MonierLifetile
  • Vande Hey-Raleigh
  • Westile

Where to Buy Clay Roof Tiles

  • Altusa, Clay Forever LLC
  • Ludowici Roof Tile
  • MCA Clay Tile
  • U.S. Tile Co.

-- Adapted with permission from Best Practices Guide to Residential Construction.

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Frequently Asked Questions (FAQs) about clay tile roof slopes & requirement for underlayment

Question: What is the minimum slope for a tile roof?

(Feb 18, 2013) what is minimum roof degree requ said:

what is minimum roof degree require for clay roof tile

Reply: waterproof membrane required beneath roofs at slope under 3:12

About minimum slope allowed for clay tile roofs or other tile roofs, if you read through standards such as ICC-ES-ESR2015 "Concrete and Clay Roof Tile Installation Manual for Moderate Climates" (copy on file) you'll see that there is no prohibition of clay tiles on low slope roofs. Rather for slopes at 3:12 or less the installer is required to install a BUR or similar waterproof membrane on the roof below the tiles.

The document I cite is available from the Roofing Institute - the Western States Roofing Contractors Association (TRI/WSCRA) and other sources.

I give contact information for the Tile Roofing Institute in the article above,

Question: why do I see daylight through the tile roof? Does that mean it leaks?

(Jan 25, 2013) Anonymous said:

I am in process of Purchasing a home with spanish clay tile without underlayment. We checked for water leaks and surprisingly there are none but on a sunny day, we can see the light poking through the holes...How could that be? Can someone advise if it is safe to purchase it. There are [no] water stains either

5/2/2014 Rob said:

Hi anonymous, hopefully I can catch you. I am curious about what happened in your situation. I just found out that the home I really want to buy has the same problem with no underlayment (concrete tiles,not clay).


Rob and Anon,

On some roof designs, particularly if there is sufficiently steep slope, in the attic one might observe daylight filtering in through the roof covering for a slate or clay tile roof that is installed on spaced nailers. The roof may never leak, given pitch and adequate head lap of the slates or tiles, OR it may leak horribly if there is wind-driven rain blowing water up-slope.

In that circumtance on an older home the observation of leak stains on the nailers or on the floor below would be helpful clues telling us that the roof has or has not leaked.

"Safe to purchase" is too big and vague a question to answer by text with almost no information about a building.


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