Dgold
Avoid DIYer
I vote for no chair rail under the archway...
I think that just lowering the ceiling a bit w/ the arch going to the existing walls may provide enough seperation....especially with crown moulding and different paint colors.
Agreed. A lowered cieling (via an arch or straight), combined with crown molding for each room would be enough.
As for the chair rail, it can continue from one room to the next, but is typically reserved for dining rooms and kitchens, where people are more likely to be sitting on chairs near the wall (hence the name). Of course these days, people put chair rail all over the place, but by keeping it exclusive to the dining room creates another element contrasting the two rooms.