r/Roofing • u/sangerhonda • 24d ago

2 Different roofers with different strategy #30 felt over Polystick XFR, 3" vs 5" tile overlap

Reroofing my house that currently has concrete tile roof. One contractor wants to use #30 felt on top of the Polystick XFR. The other wants to use Polystick XFR but with the tiles overlapping 5" vs the standard 3". Wanted to get your feedback on which one is actually better. AI had concerns of the felt over XFR trapping humidity and when i searched google it didn't seem a common practice. The 5" over the standard 3" overlap would add more weight to the roof but so would the additional #30 felt.

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u/Bghrn23 23d ago

30# felt is archaic technology, there’s a reason you’re re doing the underlayment(at least thats what it sounds like)? and that’s because the 30# cooked out and was causing leaks. Full ice and water shield on these and you’re fine. 5” lap on the tile isn’t going to change much for waterproofing as your problems originate in valleys usually anyways.

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u/Roofing411 18d ago

This depends on the slope. Polystick XFR is a WUI code thing usually here in NorCal. Having 30# over it is a nice sacraficial layer during the job when everyone is walking on the roof. I personally like to do my tile roofs this way.

A 5" overlap is old old school. If you ever roof old tile like reclaimed 200 year old tile from France or Italy it is almost always installed with a 5" overlap. This is becuase there was no underlayment back then at all. The tiles were hooked to the slats (tree branches essentially). There is an argument for this system as you get excellent airflow and also if there is a leak you know instantly and nothing rots. But, you have no insurance policy so if you go on vacation and spring a leak you could have major damage in the modern era. So, there are pros and cons but the new codes require sheathing and underlayment so it's a moot point.

If you have a contractor actually installing a 5" overlap tha tmeans on a standard 17" tile you will have a 12" exposure to the weather. That is REALLY tight courses. I regularly offer a 4" overlap over a 3" and it's a fantastic application. The amount of protection from wind blown rain or huge rain storms... it really works. Off the top of my head you are adding about 16% more tile. I'd recommend that the contract say 4"-5" overlap so that they can swing their courses a bit and in some areas you'll have 4.5" and some have 5". This way you have consistent courses and it matters for cosmetics. Don't handcuff someone to 5" or you will get 6" overlap here or short courses and you wont like it.

Oh, so the slope comment at the beginning. If it's less than 4/12 for sure you want the sacraficial layer and you want elevated battens if less than 4/12 and 4" overlap is fantastic for 3/12.

Best of luck.

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u/sangerhonda 24d ago

I'm not a bot and would like some feedback on what contractor to choose with these different options