When installing floor joists in California residential construction, what is the maximum allowable notch depth in a 2x10 floor joist according to the CRC?
Correct Answer
C) 1.5 inches
CRC Section R502.8.1 limits notches in floor joists to 1/6 of the joist depth when located in the outer third of the span. For a 2x10 joist (actual depth 9.25 inches), the maximum notch depth is 1.54 inches, making 1.5 inches the practical maximum allowable notch depth.
Why This Is the Correct Answer
CRC Section R502.8.1 limits notch depth to 1/6 of the joist depth for notches in the outer third of the span. A 2x10 joist has an actual depth of 9.25 inches. Dividing by 6 gives approximately 1.54 inches — making 1.5 inches the practical maximum allowable notch depth under the code. Exceeding this depth structurally compromises the joist's load-carrying capacity.
Why the Other Options Are Wrong
Option A: 2.5 inches
2.5 inches would significantly exceed the 1/6-depth limit for a 2x10 joist (maximum ~1.54 inches). A notch of 2.5 inches would remove more than 1/4 of the joist's depth, severely weakening its structural integrity under floor loads.
Option B: 3 inches
3 inches is also far too deep — it exceeds 1/3 of the joist depth and would create a serious structural deficiency. CRC R502.8.1 would not permit a notch anywhere near this depth in a 2x10 floor joist.
Option D: 1 inch
1 inch is below the calculated maximum of ~1.54 inches and therefore a more conservative (but overly restrictive) choice. While 1-inch notches are acceptable, the question asks for the MAXIMUM allowable depth, which is 1.5 inches (the practical application of the 1/6 rule).
Memory Technique
Remember 'Notches = 1/6, Holes = 1/3.' Holes through joists are allowed up to 1/3 of the depth; notches are more restrictive at 1/6. For a 2x10, think: actual depth is about 9 inches, divide by 6 = 1.5 inches maximum notch. This '1/6 rule for notches' is the key formula to memorize.
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