sistering a cracked roof rafter

Sistering a cracked rafter usually involves fixing a new timber rafter alongside the damaged one so the load is shared safely. The roof may need temporary support first, then a matching or suitably sized structural timber is positioned beside the cracked rafter and securely fixed with structural screws, bolts or nails, sometimes with approved adhesive as well. The new timber should extend well beyond the damaged area and bear properly at each end. Because rafters are structural, a roofer, carpenter or structural engineer should assess the crack and specify the repair if there’s any doubt.