Breather membrane under bitumen sheets?

[PeterOR]

I'm putting corrugated bitumen sheets on the roof of a garden building. The roof is a pent design, with a pitch of 10 degrees, and is boarded with 18mm osb.
Is it recommended to put a breather membrane on the osb before laying the bitumen sheets?
Thanks

 

[catlad]

No

 

[PeterOR]

Thanks, catlad. Is there a reason for that, or is it just not necessary?

 

[freddiemercurystwin]

How will breathable membrane breathe with a non-breathable layer directly above it?

 

[PeterOR]

Through the eaves? Also, bitumen roofing sheets are (hopefully) waterproof, but they can still let air through at the overlaps.