Licensed professionals qualified to conduct inspections and do evaluations concerned with strength and stability of structures, including buildings and retaining walls.
When there are any concerns regarding the strength of a building, or when contemplating a roof replacement with heavier material or addition or change in the structure where original structure is removed, it is best to hire a licensed structural engineer to evaluate the situation.
Sometimes, as an example, an owner will have replaced a portion of exterior walls with glass doors to enhance their enjoyment of a view. Unknowingly the owner removed an element (the wall) that was needed for sheer support in case of an earthquake where twisting forces could compromise the support.
Such situations are avoidable when proper Building Department reviews, permits and inspections are done. Thus when looking at remodeled properties, it is recommended that all building permits be examined.