Sometimes in older buildings, walls bow inwards or bulge outwards, depending on the type of structure and the age / condition of the building. Sighting down the exterior of a building from a distance may reveal these issues, followed by a formal building survey to discover the root cause of the deformation.
Water stains on walls may point to infiltration from horizontal elements such as doors, windows and roof junctions.
Operation of doors and windows may be affected by structural elements in walls that are deteriorating or failing.