# Clay Roof Underlayment



## Mike Lamb (Nov 12, 2008)

Looks like clay on top of an old 3 tab asphalt. There is an apparent roofing underlayment under the clay and on top of the old roof. I know the clay roof is only as good as the underlayment. What are your thoughts on this installation?


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## Ed the Roofer (Sep 15, 2008)

Is that a 2nd asphalt shingle roof on top of the visible 3-tab, or a 90# granulated roll roofing material in place?

It would seem, due to the severity of the moss build-up along the tile enclosures, that there is not sufficient slope to allow the water to drain properly, or that the overhanging edge of those 3-tabs are curling up, preventing the drainage into the gutter.

Otherwise, there may be moisture getting under the tile roof on a continuoing basis, creating that effect.

That is not how I would install such an expensive roof material on an inferior substrate and uneven moisture barrier underlayment.

Ed


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## English Roofer (Dec 26, 2008)

Hi MIke, some interesting photos!, as Ed says it looks like theres not enough overhang in to the gutter of either the asphalt or the tiles, the minimum overhang of the tiles should be at least 50mm(2") what is happening is the water is dripping off the end of the tiles and running back on its self(*Capillary Action).*
If you can get on the roof try removing some tiles further up the roof and see if there is any water penitration there, if not your only problem is extention the botton few courses of tiles down further in to the gutter and maybe use some torch on felt made in to drips in to the gutter, hope this makes sence.
Cheers
Dave

P.S. Its a shame because the tiles look good!


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## Mike Lamb (Nov 12, 2008)

I was looking through the NRCA and could not find a spec on tile overhang. This roof had about a 1" overhang. Does it matter if there is a gutter?

English, do you have a reference for the 2"? I also realized after reading the NRCA that this is a cosmetic roof since the pitch is less than 4:12.


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## Grumpy (Oct 29, 2008)

It does look like shingles. In the old days clay roof underlayment was actually smooth bur. Perhaps they used a granulated cap sheet with the smooth bur?

Naaa... chances are some hack installed the tile over shingles LOL. Look at the old gutter straps, those are always a problem for ice damning. 

I'm an advocate of always tearing off before installing new when ever possible. However if they wanted a warranty I wouldn't install the tile over shingles. 

I did install solar roofing tile once over a fire rated self adhering modified. We used FR because the solar tiles are pretty much constantly at 200* F. 

You can go to Ludowici's website or US tile or any other tile manufacturer to get a spec. I might have the Nation Tile Institute's manual which at one point 2 or 3 years ago was available for download but now you have to buy it. I'll have to look for it.


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## Grumpy (Oct 29, 2008)

BTW when you repalce that roof, install a new "high back" gutter.


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## English Roofer (Dec 26, 2008)

Hi Mike, the following is from www.monier.co.uk, which is a large clay tile producer in the U.K.

*How much should an eaves tile overhang into a gutter?* 
With most interlocking tiles it is possible to set out the spacing of the battens to ensure a whole number of tile courses in any rafter length except for very short distances between fixed points. Tiles should not overhang gutters by more than 50 mm measured horizontally from the fascia board. Overhangs greater than this will result in rainwater running off the tiles overshooting the gutter. In addition, cleaning the gutter becomes extremely difficult. If the overhang is less than 50 mm the rain is likely to be blown onto the underlay and accelerate its decay. In addition, the eaves course is likely to sprocket as the weather bars at the tail of the tile will lift the tile off the fascia board. 

Hope this helps
Dave


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## tinner666 (Oct 28, 2008)

1-1/2" is the minimum I've used for years. In the states, it's become normal to see the decking stop behind the fascia. It used to uverhang the fascia like it's supposed to, to alleviate capillary actions. I usually pull the bottom plank and set it out 1/2".


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## carlsguide (Feb 27, 2009)

I agree with English Roofer.


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## tinner666 (Oct 28, 2008)

Wow. I jusr read my earlier answer. I must have gotten confused by reading 2-3 forums at once. 
I have been setting tiles between 1-1/2 and 2". Some real life situations have dictated slight changes to go with the flow.

Thanks for the correct answer Dave.


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## Jasonthompson (Jan 25, 2010)

U need 11/2 to 2in over hang plus clay tile only displaces 80% of the water and the rest is upto ur underlaminet


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