Your lightmap resolution is too low. Also, your Uvs are not very good–you used an automatic method which creates too many UV islands which will require a high lightmap resolution to get good results. Also, it looks as though you have some surfaces like caps on your walls which are not necessary and should be deleted.
For interiors you should separate out by parts–so ideally you can do the walls as one object, floor, ceiling, etc. rather than all of it together.