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

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

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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 (Steve Bliss, J Wiley & Sons) , 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] 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 (Steve Bliss, J Wiley & Sons) , 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")

Where to Buy Concrete Roof Tiles

Where to Buy Clay Roof Tiles

- - Adapted with permission from Best Practices Guide to Residential Construction (Steve Bliss, J Wiley & Sons) .

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Reader Comments, Questions & Answers About The Article Above

Below you will find questions and answers previously posted on this page at its page bottom reader comment box.

Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

On 2021-03-18 by (mod) - Underlayment thickness requirements below clay tile roofs in high wind zones

@Carmen Gintoli, If we're talking about the same thing, "sheathing" refers to the (usually) plywood roof deck nailed to the roof structure or rafters; for most buildings, regardless of wind zone, that's nominal 1/2" CDX plywood.


If you are actually asking about underlayment, or felt or other membranes, that's given in the article above on this page.

For high wind zones you'll want to see the Underlayment Specifications (there 1-ply and 2-ply methods)

given in FRSA/TRI FLORIDA HIGH WIND CONCRETE & CLAY TILE INSTALLATION MANUAL [PDF] https://inspectapedia.com/roof/Florida-High-Wind-Roof-Tile-Installation-Manual-TRI.pdf

You will see on p. 1 that the thickness of underlayment depends on what underlayment product you're using, e.g. felt vs. self-adhered . So, sorry, but there is no 1 right answer to your question.

For example: (EXCERPT - NOT THE FULL DATA)

Asphalt Saturated Roofing - Organic, Type II, commonly called No. 30 or 30#, conforming to ASTM Standard D 226, Type II organic saturated.

Mineral Surface Roll Roofing - Shall be a minimum of seventy four pounds per roll commonly called 90#, conforming to ASTM D 6380.

Modified Bitumen Membrane - Shall conform to ASTM D6162, D 6163 or D 6164.

Self Adhered Membrane - Self Adhered products shall meet ASTM D 1970, underlayment thickness, minimum thickness 40 mils. Self Adhered products shall meet the following testing standards: ...

The clay tile roof underlayment table below is again an incomplete excerpt - and is from p. 3

On 2021-03-18 by Carmen Gintoli

What is recommended thickness of sheathing under a clay tile roof in high velocity wind zones; e.g. 160mph? Live load of 20psf.

On 2021-01-22 - by (mod) -

Mike:

Yes you can but you'll need to mechanically secure certain courses.

Please see your question repeated and my detailed reply at

CLAY TILE ROOF CONNECTIONS https://inspectapedia.com/roof/Clay_Roofing_Tile_Connections.php

where we discuss foam-adhered clay and concrete tile roofing

On 2021-01-22 by mike

can i foam tile on a 7 on 12?

Reader Question: my roofer says felt underlayment is not necessary

Clay tile roof battens © D Friedman at InspectApedia.com 2016/03/21 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"

Paul,

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 InspectApedia.com

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.

Also see CLAY TILE ROOF SPECIFICATIONS and for more roofing felt / underlayment advice from our expert Steve Bliss

see ROOFING UNDERLAYMENT BEST PRACTICES

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

On 2021-01-22 by (mod) - additional fastening when using foam adhesive on clay tile roofs of 7/12 & steeper slopes

Using Foam to Install Clay or Concrete Roofing Tiles

Example of tile roof underlayment specification for Florica - adapted from FRSA's roofing guide, cited & discussed at InspectApedia.comBottom line: yes, you can use foam on a 7/12 clay tile roof but you'll need to mechanially-bond every tile in the first course and every third tile of the fifth course in addition to the tile adhesive.

Please see your question repeated and a detailed reply including reference and source citations, documents, and clay tile adhesion (using foam) guideline documents found

at CLAY TILE ROOF CONNECTIONS

On 2021-01-22 by mike - can i foam tile on a 7 on 12?

can i foam tile on a 7 on 12?

On 2020-09-25 - by (mod) - OK to use spray foam adhesive on tile roofs in Florida

OK to use spray foam adhesive to install clay tiles in Florida?

Anon

Yes. Please see details at CLAY TILE ROOF CONNECTIONS

Tile shall be attached to resist the aerodynamic moment as determined when using the design pressures for the building and the attachment calculations set forth in the local building code.

Starting at the eave, make certain the tile overhangs the drip edge uniformly along the first course. The tile shall over-hang the eave line by at least 3/4" but not more than 2”.

Secure tiles with Nails, Screws, Foam/Adhesive or Mortar. See Attachment Resistance Values per Tables 1 & 2 in Appendix A.

Cut/break tile for proper staggering of tile courses when using staggered/cross bond method of installation.

Set tile in stepped course fashion or in a horizontal and/or vertical fashion when utilizing straight bond method.

Lay succeeding courses of field tile in same manner. Cut/break field tile to form straight edge at center of hip/ridge. - original source: Eagle Roofing, eagleroofing.com/installation_guides/Florida.pdf

On 2020-09-25 by Anonymous

Hi, I live in south florida and I have a 4:12 flat tile roof.My roof was leaking and I called a licensed contractor to repair it. His crew removed the tiles which were nailed to find the area and fix it. When they were reinstalling the tiles after installing underlayment they did not nail even a single tile except the tiles in last row at the roof edge.

The used some foam spray to lay tiles for may be 10 rows of tiles continuously. I want to know is it safe to install tiles like this. They said nails cause roof to leak so we dont use nails. However they did use nails on the underlayment.

On 2020-07-16 by steve

what underlayment should go under clay tile

On 2019-08-23 - by (mod) -

Neil

In the roof design you describe in which we're really relying on the underlayment, the usual materials are modified bitumen or occasionally EPDM.

What would make sense when replacing the valleys on the tile roof would be to remove enough tiles to lay down ice and water shield under the valley, out to sufficient width (36" may not be enough if the roof includes low slope sections)

or as some roofers do, install over that metal valley flashing whose edges are folded up to create a water seam to keep water from running out past the flashing edges.

An "open" valley means that the roof tiles do not cover the actual valley: an area of exposed valley flashing is left to drain - typically several inches wide.

A "closed" valley means that the roof tiles completely cover the valley - it's underlayment or flashing is still needed and must be present, but it's not visible.

The advantage of closed valley is that the roof tiles protect the valley flashing from sun and weather exposure, greatly extending its life - provided no fool drove nails through the valley flashing while installing the roof tiles.

ROOF FLASHING, ASPHALT SHINGLE VALLEYS

illustrates these details

On 2019-08-22 by Neil

The tile style and installation on this 100+ year old building, as you suspect, is using the tile to shed the majority of the water but the real "water tight" performance comes from the underlayment. The underlayment around these valleys is currently watertight but when the valley's are replaced he will have to try to weave new underlayment with adjoining 50+ year old felt. I am not clear on open or closed valley but will find out.

The reason the insurance co is wanting to use this method is that the tile style is no longer available and there is barely enough tile available to repair the hail damaged tile.

To repair the valley correctly (vertical tile removal from the peak to the eave) would end up needing more tile. But in the future if leaks develop around the weave our insurance could be voided since this shortcut method likely wouldn't be done if sufficient tile was available. We feel any disturbance of that older felt is creating a problem we don't currently have.

On 2019-08-09 - by (mod) -

Neil I'll be glad to help but first have to understand the situation. I'm unclear on exactly what's meant by "a process that only runs parallel to the valley"

Underlayment beneath a tile roof might run parallel to the eaves and repairs to a valley might certainly require just removal of roof tiles in the vicinity of the valley sufficiently wide to permit installation of a new valley underlayment (possibly also valley flashing) and then replacement of valley tiles.

Is it a "closed" or "open" valley - photos would help alot here.

I SUSPECT *(as your roof construction is not actually given here) that the roofer is concerned that just laying felt under the valley area would not prevent other water that penetrates the tiles from running under the valley underlayment and thus leak through the roof.

That is a very significant concern in particular if your style of clay tile roofing is not actually relying on the tiles themselves to shed water off of the roof. That design is common in some countries and cities such as parts of Florida in the U.S. in which the clay tiles are cosmetic and the actual waterproof roof is provided by an underlayment.

Other clay tile roofs such as ours here on the other side of your wall - in Mexico - depend on the clay tiles themselves to collect and shed water off of the roof; in that case the underlayment is principally cushioning the underside of the tiles and giving a bit of extra leak insurance.

Those are two different clay tile roof approaches.

In any event, If the roofer uses a high-tack adhering ice and water shield I'd expect the valley underlayment to bond with the existing underlayment so as not to allow water to pass under the valley underlayment. Ask your roofer what kind of roof you have and whether or not she can use an adhered valley underlayment.

On 2019-08-09 by Neil McNeill

In repairing the hail damaged tile roof on our Church our Insurance Co wants us to repair the valley damage using a process that only runs parallel to the valley.

Our Roofer, who both they and we agree is very competent, does not want to warrantee that method since he'd have to try to blend new underlayment (running parallel with the valley) with the current underlayment that runs parallel to the eaves. He has recommended removing tile vertically from the peak of the valley so that he can install the underlayment parallel with the eaves -

I can only find IBC codes that support his approach. Does anyone have any advice on how to force the insurance Co to agree to the method our roofer recommends and the IBC codes require?


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