Older buildings floor joists were not designed by mathematical means. Joists were sized empirically based on experience. Joists are often small by modern standards. Some deflection or springiness is common.Local overloading under the weight of partitions or load concentrations is also common.
When a change of use occurs, floors may become more heavily loaded than they were designed for. Whether this defect is serious or not, it's a matter of degree on facts in each case. Cracks between wall and ceiling greatest at mid span. Cracks between external walls and partitions become grater with height. this is often not visible as filled during previous redecoration.Door openings in partitions distorted. Often a small crack above door to ceiling. Floor sag. Ceiling crack beneath.
How to find out if my floor is overloaded?
- Deflected, sagging floors. May be localized if uneven load
- Springy floors
- Door openings out of square, doors may bind or have been cut out of square to fit
- Separation of internal walls from external walls, widest at top
- Ceilings crack beneath
- Crack sometimes between door head and ceiling