Double Ceiling?

[Pettttter]

I have sloped ceilings made of drywall and want to switch to some form of plank ceiling. Is there any reason to tear down the drywall instead of just nailing planks directly onto the drywall?

Behind it is battens/vapor barrier/insulation/air gap/sheathing/felt if that makes any difference.

 

[Oldboy]

If you know where the glesen is, I see no reason to tear down the plasterboard. You can possibly lay lumppapp in between to reduce the risk of gnirp and creaking.