According to the CRC, what is the required minimum depth for notches cut in the top or bottom of floor joists?
Correct Answer
B) Maximum 1/6 of the joist depth
CRC Section R502.8.1 limits notches in the top or bottom of floor joists to a maximum of 1/6 of the joist depth. Notches must not be located in the middle third of the span and holes are limited to 1/3 of the joist depth with specific diameter and location restrictions.
Why This Is the Correct Answer
CRC Section R502.8.1 limits notches in the top or bottom of floor joists to a maximum of 1/6 of the joist depth. This restriction preserves the structural integrity of the critical tension and compression zones at the top and bottom of the joist. Notches deeper than 1/6 of the joist depth can significantly reduce the joist's load-carrying capacity.
Why the Other Options Are Wrong
Option A: Maximum 1/3 of the joist depth
1/3 of the joist depth is the limit for holes bored through the joist web (not notches). Notches at the top or bottom are held to the stricter 1/6 limit because they cut into the structural flanges. Confusing the 1/3 (holes) with 1/6 (notches) is the most common error on this topic.
Option C: Maximum 1/4 of the joist depth
1/4 of the joist depth is not a code-specified limit for joist notches. While it is between the hole limit (1/3) and the notch limit (1/6), it is not the correct value found in CRC R502.8.1.
Option D: Notches are not permitted in the top or bottom of joists
Notches are permitted in joists under strict conditions — they are not categorically prohibited. They must be located in the outer thirds of the span (not the middle third) and must not exceed 1/6 of the joist depth.
Memory Technique
Use the rule of sixths and thirds: 'Notches are narrow — 1/6. Holes are bigger — 1/3.' Picture a joist: notches at the edge (top/bottom) are the most damaging to structural integrity, so they get the tighter limit (1/6). Holes through the web are less critical, so they allow 1/3. '6 for notches, 3 for holes.'
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