Q. This week: My house is about 70 years old and the floors on the first story shake when someone walks on them. The problem, I think, is that the floor joists are too narrow. They're only 7.5 ...

Let’s first discuss the span tables that Stewart mentioned. A span table is a chart that shows how far a certain floor joist can span and not bend too much, depending on several factors.

Let's first discuss the span tables. A span table is a chart that shows how far a certain floor joist can span and not bend too much depending on several factors.