We received a call recently from a
homeowner who had a problem
he wanted us to solve. He had just built a
garage with living space above, and the
upstairs floor was too bouncy. The odd
thing was that the homeowner had
specifically asked the building designer to
ensure that the floor was very stiff, so the
designer had specified floor joists (wood
I-joists, in this case) with an L/720 liveload
deflection limit. So why was the
floor so springy?
The problem, as it turned out, was
the midspan girder that the joists
crossed. Although the girder had been
sized correctly by "code" for strength
and stiffness, its deflection limit was
much greater than that of the