A room addon is simple a room addon.... 4 example u add yr room addon into a normal room and set it where youd like it to be, most ppl set the basement under the room 4 example.. room addons do not hold nodes to load furniture into because it is a furniture its self.. so what u need to do is load the furniture into the room youv added the addon basement into and dragg the furniture into place by useing CTRL move left or right, and SHIFT to move up or down.... DO NOT clik and drag furniture directly into a addon, u need to SLIDE it into it by usen shift or ctrl