Hello! The word ‘thiar’ literally means ‘situated in the west / behind’, so I would rather go for ‘siar’ (‘leading to the west’) and use “An teach ar an mbealach siar” (“The house on the westward road”). But I suppose, you might as well leave out “an teach” (“The house”) and just write “Ar an mbealach siar” (“On the westward road”), as the object referred to (house) is already made clear by the context.