Hi Tim

I looked up binding beam and binding joist and binder in several dictionaries and the short answer is it is the same thing as a sleeper. It is a beam which long joists cross over for intermediate support. One dictionary even listed a "binding rafter" which was defined as a "longitudinal timber in a roof supporting the rafters between the comb and eave" in other words a major purlin!

A binder can also be called a bridging joist. A floor built using a binding beam and joists is called a double floor.

Lexicon!