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

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This article series explains clay tile roofing types, clay roofing tile inspection, tile roofing diagnosis, & tile roof repair.

Tile-Covered Roof Installation 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.

Article Contents

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] I know these tables are too small, but if you click to enlarge them they're all very readable. Apologies. Editor.

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.

Roofing Felt / Underlayment Requirements for Clay Tiled Roofs

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

[Click to enlarge any tables or images in these articles.]

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.

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

This article includes excerpts or adaptations from Best Practices Guide to Residential Construction, by Steven Bliss, courtesy of Wiley & Sons.

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

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.

See ROOFING TILE SHAPES & PROFILES for the basics of roof tile profiles and what they mean.

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:

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

Reader Question: my roofer says felt underlayment is not necessary

Clay tile roof battens (C) D Friedman2016/03/21 Paul Smyth said:

Two weeks ago I had a large fir tree branch fall and break (13) tiles on my roof. The roof let water fall all of the way to our Hardwood. When we asked the contractor about installing under all the tiles, to meet code.

They said they only had to put tar paper around where the tiles were broken. Is the contractor right? When the hole was open we could see that none of the tiles had no underlayment.

We could see the sky! Please call me @623-249-3549 or send an e-mail. Please refer me if you can not provide the answer Thanks

This question was posted originally at ROOFING FELT UNDERLAYMENT REQUIREMENTS

Reply: "meets code" vs. "meets roofing manufacturer's specifications" vs "good building practices"


I can't quite offer an authoritative citation as I don't know where your property is located, what codes apply nor exactly what sort of tile roof is installed.

"Meets code" is a mis-used and mis-applied claim and approach to good building practices.

Building codes are a minimum standard. At the end of the day, your roof needs to meet the roofing manufacturer's installation specifications.

If you insist on relying on "meets code" as basis for an argument, then you need to find, in your local, state, or provincial building codes, the code section that says (as most codes do) that the product must be installed following the maunfacturer's specifications.

Some tile roofs absolutely rely on the underlayment to prevent leaks, where the tiles themselves offer only sun protection for the underlayment and of course an aesthetic roof topping. Such roofs are common in the South and Southwestern U.S. (for example).

Other tile roof systems rely on the tile design and installation to shed water effectively, using the underlayment as a surface padding, as leak protection during installation. Such roofs are found in Norway, northern Europe, and in the Northern U.S. such as in Minnesota. You'll find photos of all of those tile roof examples here at

If you know the specific roofing tile product, we (or you) can find its manufacturer, then find the manufacturer's roofing tile installation specifications. That will put an end to the arguing and finger-pointing.

Watch out: keep in mind that as your roof is now installed, only if the roof leaks would it make economic sense to remove the whole installation to add the missing felt.

Paul, also see our excerpt from Best Construction Practices (Bliss) in the article above beginning at CLAY TILE ROOF UNDERLAYMENT REQUIREMENTSwhere we will re-post your question, our detailed reply, and any further references we can dig up.

for more roofing felt / underlayment advice from our expert Steve Bliss

Watch out: also, if your roofer did not install roofing felt / underlayment that is required by the manufacturers' specifications, your roof warranty may be voided. See WARRANTIES for ROOF SHINGLES

Clay Tile Roofing Materials, Methods, Standards

Where to Buy Concrete Roof Tiles

Where to Buy Clay Roof Tiles

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


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