Underlayment fastening

I'm soon removing 25 year old composition roof and tarpaper, to replace with titanium underlayment, then metal roofing panels, of the sort where the fasteners for panel 1 are hidden by panel 2, which snaps over the fasteners.

So to fasten the underlayment, I have tin caps. Roof square footage is 3950, I will do in 4 sections. Metal salesman recommended hammer stapler to hold the tin caps down. I would like to know any other recommendations for the tin cap fastening.

Thanks in advance.

40 square is no small task. If you are doing it when it is going to be left open in sections, I would definitely get a plastic cap stapler like a Stinger. Little bit of an expense over just the fasteners, but so much easier.

Thank you. Is there any issue with the caps or their profile beneath the roof metal panels showing though?
Thanks again.

Not usually. If it isn't staying exposed for a while, you can just staple it down.

I have a very similar situation (large 4K+ s.f. with snap standing seam) and also want to staple underlayment with caps due to an unavoidable long exposure time. Both metal options we are considering (ABC's SL16 and Ideal's HF Jr) are 29 gauge - so thin. Worried about the plastic caps interfering with the metal install or printing through. Is there a reason you recommended plastic caps over the original tin cap suggestion? Just speed?

I've completed 3 of 6 roof surfaces by removing old shingles and tarpaper, replacing some of the decking, then stapling Titanium 30, using tin caps, DuoFast 5020 pneumatic stapler and and 1/2" wide 1/2" long staples, then installing the CFS panels. Exposure time was 2 weeks, including a few heavy rains, no leaks.

The main problem I had was the stapler would at times punch the staple all the way through the tin cap, which is easily resolved by lowering the air pressure. When these staples are seated, they seem to grip really well.

For the large roof surface (23' by 70') I bought an additional (cheapie) stapler, which seems to work fine, just may not last as long as the 5020. I think I will need to order another box of 5000 staples.

For the remaining sections, I plan on replacing all of the decking, the original decking was installed in the year following Hurricane Andrew, and is sub standard, sags terribly, and some pieces are completely spongy.

Best luck with your project.