Roofing Felt Under Tin Roof?

[SansPlans]

Hi,
So I'm done framing my roof mostly and put some roofing felt on it to protect everything until I can buy the tin roofing.  I overheard at a building class this weekend some old crusty guy say "Well you can't put felt under a tin roof." Is that true? I thought, since I had read you could just put the tin roof right over old shingles in some cases, that it would be ok if I put roofing felt up temporarily and then just put the metal roof on top of that.

Can anyone clarify which is true (felt is ok under tin or it is not ok) and why that is the case?
Thanks!

[Kevin]

for my metal roof the instructions said to use 30lb felt.
Kevin

[JRR]

Not a trusty crusty!

[glenn kangiser]

I don't see anything it will hurt.  I put felt under my old corrugated tin roof because the tin was used and had lots of nail and bullet holes.

[Okie_Bob]

Glenn, you need to get Sassy to take that target off your back! Gonna get you hurt someday.
Crusty old nut if you ask me, I wouldn't put up a metal roof without 30# felt!
Okie Bob
PS: and I did put 30# felt under my metal roof, both of them

[Redoverfarm]

I put a roof underlayment under the tin I installed.  Never relly gace it a though but I put the metal over sheeting.  If it relly doesn't make a difference I think the majority of people do as it is a weather proofing for their house until they can get a permanent cover on. And it would be silly to take it off at tin installation stage.  I guess an exception would be when installing the roof over perlins.

[glenn kangiser]

Tin could get hot over the tar but that is the only problem I can think of.

I measured ground temp in full sun here at 134 degrees f.