Because floor joists typically support tremendous weight from subflooring, floor coverings, appliances, and furniture, they are subject to great stress. Some of these joists may crack under this stress. Others are weakened during installation. As a result, some joists develop splits or cracks.
Floor Joist Crack Causes
Floor joists can become cracked for various reasons.
The joist may support more weight than other adjacent joists because it is installed slightly higher. A joist slightly bowed may support more than its share of weight at the bowed section of the joist. And joists may split and crack at the end where bolts attach them to the building structure.