Final answer:
The question involves construction framing, discussing the proper sequence for nailing bridging in a floor system. Top bridging is nailed before, and bottom bridging after, the subfloor is installed.
Step-by-step explanation:
The question appears to be related to construction framing techniques, specifically the process of installing bridging in a floor system.
Bridging refers to the installation of small pieces of wood or metal between joists to stabilize the structure and distribute loads more evenly. In typical construction practices, the top portion of the bridging is secured to the joists before the subfloor — the structural surface lying underneath the final flooring material — is nailed down. After the subfloor is securely attached, the bottom portion of the bridging is nailed.
This sequence helps in maintaining the structural integrity of the floor system, preventing joists from twisting or moving out of place during construction and over the life of the building.