There is no statutory duty to effect improvements, but you must not cause the building to fall into any worse state than it was in when you became its owner.
Nid oes dyletswydd statudol i wneud gwelliannau, ond mae'n rhaid i chi beidio â pheri i gyflwr yr adeilad fod yn waeth nag ydoedd pan ddaeth yn eiddo i chi.