Doing inspections for the last 30 years, with most of my work on wood framed residential structures, I commonly find floor slopes at the second floor of a structure which indicate some sagging of the structure has occurred.  Often such sagging results in floor slopes which are significant and noticeable, but do not indicate an abnormal degree of deflection in the sagging members and do not require structural repair.  The observable slopes occur even with small acceptable deflection ratios because of the configuration of the floor structure and supporting walls.

While reviewing may daily email I ran across this short article in the Journal of Light Construction {Click Here for Article} which covers the most common causes of irregular floor slopes in two story stacked construction and how to avoid them.  The list is inclusive of the most common causes of uneven floors and the subject is well explained making it worth sharing.  I often find the JLC has good topical articles worth the review.

Commonly irregular floor slopes occur at locations along second floor walls due to sagging floor joists occur over a long span of a room below and adjacent to a stacked common wall where the decking spanning the wall and joists must make up the elevation difference between the sagging joists and the stiff wall below, or where this is a significant change in configuration of the floor joists where they change direction or length creating a similar effect.  Such slopes are sometimes found in custom construction due to the longer spans encountered in this price range, but most often occur in production construction due to expediency in completing construction, oversight, or costs savings.  These irregularities can often be prevented through careful planning during the design phase of construction.

This may help you to understand why and where second floor slopes most commonly occur. If you are still unclear on how these configuration issues result in irregular slopes feel free to drop me a note.

Journal of Light Construction – Framing Trouble Spots