I have been contacted by a friend that is building a log cabin. He has approved and stamped drawings, but the designer has designed timbers 8-3/4 x6 x 15'-4"long span for the floor joists 36" on ctr. He would like to use logs in liew of timber. he has asked me what size logs to use. does anyone know of any sizing charts for logs, or any available formulas so we can try to figure the log diameters. any help would be appreciated, thanks,John..