Should be full thickness next too rafter.
Collar ties shall be fitted to every second pair of common rafters, or at 1200 mm maximum spacing, whichever is the lesser. Collar ties shall be fixed to rafters with one M10 bolt for ties greater than 4.2 m long or min. 2/75 hand-driven nails or 3/75 × 3.05 mm ∅ machine-driven nails for ties up to 4.2 m long.