Quick Qeustion regarding internal wall?

"Top room" means only the roof is above? If the wall is built on the floorboards it surely wasn't a load bearing wall originally. However, subsequent modifications to the roof may be tied to the wall. If you can see above the wall then look for roof braces which rise from the top of the wall. Cut a hole in the ceiling if necessary to inspect above the wall. If the entire top of the wall is free of any bracing then you should be fine. However, if there is roof bracing of any sort resting on the wall or if any of the ceiling joists are joined on top of the wall then you must install a header beam to support it.