I've designed a traditional timber frame with an English Tie Beam truss for a commercial space. My dilema is that I'm working with an engineer who is adamant that no more than %25 of the crossectional area of the timber is removed at any point in any component.
What was initially intended to be a traditional timber frame is quickly becoming a post and beam.
I'm looking for some references that could lend a different take other than this %25 rule of thumb, so some of the craft could be saved in this frame.

Thanks,

Ian