This page answers frequent questions about clay tile roofing underlayment requirements.

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

Tile-Covered Roof Installation Q&A

These questions and answers about clay tile roofing were posted originally

at CLAY TILE ROOF SLOPE, DECK & UNDERLAY - be sure to review that article.

On 2019-08-23 by (mod) - valley flashing & underlayment options on a clay tile roof

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) - types of tile roofs: how is water actually shed?

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 - best repair for hail damaged tile roof valleys

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?

On 2018-12-10 by (mod) -

Generally it's the Raptors not the sheathing that's carrying the weight of the roof. Half inch exterior rated Plies pretty coming. You might want to take a look at this document for some nice durable roof specifications

TILE ROOF LIFE (NRCA) [PDF]

On 2018-12-10 by Oscar

What type and thickness sheathing would be required for flat roof tiles? It's for a shed, but I don't think 1/2 inch OSB is good enough.

Please advise.

 

On 2018-09-20 by (mod) -

Peter

I couldn't make out the sheathing under your clay roof tiles but if it's delaminating plywood then there are leaks and the sheathing will need replacement and of course the leaks fixed.

On 2018-09-19 by Peter Kohut

Living in Florida, I’m concerned that the clay tile is laying on sheathing w/o any plywood. Additionally this sheathing is pealing on the underside. Uplift resistance is not provided. Shouldn’t this decking be replaced?

On 2017-02-11 by (mod) - In reroofing a tile roof necessary to use two layers of felt?

HH Take a look at Clay Tile Roof Underlayment requirements at

CLAY TILE ROOF SLOPE, DECK & UNDERLAY

Also click to enlarge the tables and you'll see where two-layers of felt are discussed.

Factors include the pitch or slope of the roof.

Certainly one would not rely on the old felt when replacing a clay tile roof.

On 2017-02-10 by H Hansen

We received two bids to fix a roof leak. One bidder will use two layers of 30# felt and the other one layer of 30# felt. In reroofing a tile roof necessary to use two layers of felt?

On 2016-09-13 by (mod) -

Bob,

A lot of the roof leak or failure risk element for concrete tile roofing installed without underlayment depends on where the building is located - something you didn't note.

But a review of a typical industry standard for concrete roofing tile systems will show that there is no approved, concrete roof tile recommended roof application method that omits underlayment completely. Here's an example from the Tile Roofing Instutite as provided courtesy of Eagle Roofing: http://www.eagleroofing.com/installation_guides/FRSAInstallationManual.pdf

I wouldn't place much stock in a roofer's "warranty" as protection for you either. Warranties are mostly marketing tools and won't cover the largest possible costs if a roof leaks and damages a building or its contents.

Find out exactly what concrete roofing tile product is being installed: get me the manufacturer's name and the specific roof tile product, and we can obtain a more authoritative answer.

On 2016-09-13 by Bob Culp

While replacing tiles, I observed the builder just put the concrete tiles right on the plywood roof. Is this a major problem?

On 2015-12-01 by (mod) -

There are two risks,

1. Depending on just how bad the roof is, a worker may fall through rotted sheathing and be injured or killed - this is an immediate possibility against which you should protect yourself (and other workers) regardless of other worries.

2. Nailing shingles onto soft rotted plywood means the shingles are likely to blow-off later, leading to a roof failure, water damage, litigation, and a mess.

Take a look in the attic where the roof decking is visible - look at the leak history, look for sagging, delaminating, damaged plywood. That's where your guy should be looking too.

These are some of the risks of a roof-over job when we don't do a tear-off. A builder who didin't inspect, properly size the job, is in a bind. Better to take the discovery to the client and amend the price than to do a roof job that is designed to fail.

On 2015-12-01 by Craig

I am working for a guy who is just starting a roofing business and this job we're on is an older roof that had comp shingles he is outing s tiles on 3\8" plywood that is weak and spongy. My concern is the roof collapsing yet no one wants to listen. Am I wrong?

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).

Reply:

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.

Question: OK to see light through the clay tile roof?

(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 water stains either

Reply:

(May 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).

Moderator said:

Rob, I've posted a reply and explanation about this "I see the light through the tile roof" query in the FAQs found at the bottom of the article above - that gives a bit more space. Let me know if questions remain, or if you can, use our CONTACT link to send along some sharp photos of what you see and I can comment further.

Question: which roofing felt is more durable as underlayment

(Aug 20, 2014) Jason said:
Hello, I am pulling my old 'S' tiles an replacing the felt paper. I am just finishing the back half, which I used 40 lb. saturated organic

. Is this a good product to use? the roofer i hired for the front side indicated that 30 lb. has more 'oil' and will last longer. Seems odd given they both seem to be asphalt and 40 lb. would simply have more of the asphalt. the said it was too heavy and would crack under the concrete tiles sooner. what do you think?

Reply:

Jason

I cannot find any indication in any expert resource suggesting that 30# felt is more durable than 40# roofing felt nor can I figure out where your roofer's data might come from.

The "lb" rating on felt is about how much it weighs - which is a function of the paper thickness AND the amount of asphalt in the material. (It's asphalt not oil).

So 40# felt would certainly be more durable thanm 30# roofing felt.

I do not agree with your roofer. A the risk of making him annoyed, I'd ask where his data comes from. (I suspect we already know the answer.)

...

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