A collar tie is meant to tie together the tops of opposite rafters which helps strengthen the roof and resist wind uplift forces. Collar ties are typically placed in the upper portion of the roof, usually the upper 1/3. Collar ties may not be required in certain jurisdicitions, particularly if metal connectors were utilized to attach the rafters to the ridge board. If they are required they are commonly placed at every other rafter if the rafters are on 24″ centers. The typical minimum requirement for collar ties is 1 x 4.