I have a question on building a gable roof, I installed rafters (2x6) on a 2x8 ridge beam 14'-4" length, width 13'-1" of wall. Do I have to put cross ties and how many. I have 11 rafters on each side 16" on ctr. Pitch is 4-12. The lenght of rafters is about 8'. I took the design from family handyman mag. They didn't show cross ties.