3 ply under concrete tile ?

I have a customer in southern cal. who wants me to use a 3ply mod. 40# under monier Barcelona tiles on a5/12 roof close to the ocean and I think 2ply is a good system

Right on wywoody....I continue to untangle the common/accepted misinformation regarding the proper installation of a tile roof....(That being the underlayment is the primary roof)....Many years ago while doing some research, I remember speaking with a chap in the UK, (a tile manuf. rep. of some sort), whereas he made the comment, in so many words, that...."you yanks tend to cheap'n everything-up over there"....IOW's; The predominant tile roof installations/specification are more of a temporary fixture, rather than permenant/long-term....The last home I biult for my family has a tile roof....7,500' elev., fairly heavy yearly snowfall....Guess what?....No I&W....one #30 felt....I would've put the tile right on spaced sheathing w/o any plywood/underlayment at all. if the truss co. would have been more accommodating....Just to prove a point.

If you're using battens and not elevating them for drainage, money spent for a third ply would be far better spent on a counterbatten system. Of course being in SoCal, your customer might like the thought of an extra blanket of felt cushioning the tile crushing him when the big one hits.

OK thanks for the input guys, I really appreciated Old Schools advice. I have 34 years experience myself and a 3ply tile liner is uncommon to me. A sensible reply and affordable to customers wishes.

I bet none of these products even have a 3-ply line on the rolls. You can't find a proper double two-ply line on the synthetics either. As a matter of fact, some of them have a center line that isn't even truly on the center. Better bring a tape measure and a chalk box.

If he is willing to pay for a 3 ply, give him a 3 ply.

well he has had granulated cap sheet for underlayment and the roofs orientation is facing directly towards wind driven rain off the ocean with the runoff from the second story eave and the valley from above also combining into the same water path. so all three combined with the 2" lap on the underlayment proved inadequate with other factors, poor deck preparation.bad sheathing job. improperly driven fasteners & more. That is why I am going with a 2 Ply. I've run into this before (only during the El Nino years) Thanks Brother

If the customer thinks he needs 7-10 years before he learns that water is getting under the tile, then that's the way to go. Unless it's a severe weather site, the felt will be exposed for months, or below 5/12, I never have any problems with one layer of 30 lb. My underlayment upgrade is Certainteed Winterguard HT with 30 lb over it. Piling on layers of underlayment means no faith in the tilers' ability to install a watertight roof.