Weed membrane for decking, under or over

[A_Novice]

Hi,

Have seen a couple of responses about this.

Having some decking put down.

Should the membrane go under the deck (the norm) or can it go across the joists on top?

I've read some people recommend the latter

What are people's opinions on this?

Thanks

 

[sxturbo]

Underlaying on top the joists reduces the air flow and will cause issues later down the line