Hi TMC,

Any kerf, in this method, is better than none. Box heart beams that are mostly still log, or log flattened on two opposite sides is the most common, yet I have seen it in all fashion of timber, free of heart and otherwise. This is a skill that is learn through mentorship, time, and experience (experiment,) but I will say that I have read and heard more positive of it, than negative, from those that embrace the method.

Regards,

j