Residential Building Inspector B1Floor ConstructionMedium
A floor system utilizes wood I-joists. The building plans include blocking between the I-joists at the ends and at intermediate supports. What is the primary purpose of this blocking?
- ATo prevent the joists from rotating or buckling laterally.
- BTo facilitate the installation of plumbing and electrical lines.
- CTo provide a nailing surface for the finish flooring.
- DTo increase the floor's thermal insulation value.
Show answer & explanationAnswer & explanation
Correct answer: A. To prevent the joists from rotating or buckling laterally.
Blocking between I-joists, especially at supports and where concentrated loads might occur, is critical for preventing lateral rotation or buckling of the joist web and flanges. This maintains the joist's stability and load-carrying capacity.
Why the other options are wrong
- B. Blocking can sometimes interfere with utility runs; it's not its primary purpose to facilitate them.
- C. The subfloor provides the nailing surface for finish flooring; blocking is not primarily for this purpose.
- D. Blocking provides negligible thermal insulation.
I-Joist Blocking Purpose
Blocking between I-joists provides lateral support, preventing the joists from twisting, rotating, or buckling under load.
- Crucial for stability, especially for tall, slender I-joists.
- Required at supports and sometimes at mid-span.
- Helps distribute concentrated loads.
Memory trick: Brace the Beams, Block the Buckle.