We're looking at putting up a tongue and groove ceiling in our kitchen
to match the T&G we just finished in the porch (the kitchen opens into
the porch) and we had a quick question. When we put the T&G up should
we put it directly against the joists, should be use something like
tar roofing paper first to seal the ceiling, or should we put it over
sheetrock?

There is currently a dropped ceiling we are removing so if it's best
to put it over sheetrock then we'd have to patch the ceiling where the
drop is first. Just didn't know if there was something we should put
up first before the T&G to be sure it's all sealed.

When we first did the porch we treated the top of the T&G with
Thompson's Water Sealer to be sure that the roof side is protected.
Didn't know if that was best to do here or if something else should be
attached to the joists first.

Thanks!!!