Click seam/sheet metal

[Kjell Borgström]

I was thinking of putting this on a cottage roof, just straight pieces without penetrations. I can't figure out if they should be placed on battens or directly on the underlay fabric. When reading what some manufacturers write, the metal can be affected by the butyl in the underlay fabric and also by pressure-treated wood, intended to have it in fascia boards and the roof edge board.
But my roofer says they should be screwed directly onto the underlay. I think it would get hot and also question the lack of ventilation/air gap under the metal.
Does anyone have the definitive answer or tips on what's right and wrong?

 

[RoBo]

Directly on the "pappen" works best. But it should be a "papp" for metal roofing, for example isola isosteel, there are more brands available.

 

[Alexn72]

Both are equally fine.
I laid it directly on papp. Just check that the papp is approved for it.

 

[useless]

If battens are applied, the sheet metal risks becoming striped over time.