I inspected a custom home, pre-drywall, where the beams spanning the basement ceiling, and carrying the dead load of the living room above, were over 24’ in length. The plans allowed for the span, but I thought the span was excessive. We were on the third floor over this span, when people walked in the living room and caused the top floor to “flex” up and down. Further evaluation by a structural engineer (advised in the inspection report) found the I-joists to be too light, causing a diaphragm effect between floors. All floor joists had to be cross braced in an “x” pattern to stop the floor bounce feeling. This topic may seem like a non-issue, since “builders follow the plans”, but even good plans can have flaws. We need to do our due diligence, and keep our eyes open.