When framing a header over a 6-foot wide opening in a load-bearing wall using Douglas Fir-Larch lumber in a single-story residence, what is the minimum header size required by the CRC span tables?
Correct Answer
B) 2x8 double header
Per CRC Table R602.7(1), a double 2x8 Douglas Fir-Larch header can span up to 6 feet in a single-story building with a 32-foot building width. The table accounts for typical residential loads and provides prescriptive sizing for common lumber species used in California construction.
Why This Is the Correct Answer
CRC Table R602.7(1) provides prescriptive header sizes for load-bearing walls in single-story buildings. For Douglas Fir-Larch (a high-strength species group), a double 2x8 is sufficient to span 6 feet when the building width does not exceed 32 feet. The 2x8 provides adequate depth-to-span ratio for the typical residential roof and floor loads in a single-story application, making it the minimum (most economical) compliant size.
Why the Other Options Are Wrong
Option A: 2x12 double header
A double 2x12 is significantly over-built for a 6-foot opening in a single-story building with Douglas Fir-Larch. While structurally sound, it exceeds the minimum required size per the CRC span tables, increases cost and weight unnecessarily, and would be the answer for a much wider span or multi-story condition.
Option C: 4x8 solid header
A 4x8 solid header provides roughly equivalent structural capacity to a double 2x8 (two 1.5-inch members = 3 inches vs. one 3.5-inch member), but the CRC span tables are based on double-member headers, not solid timbers, for this application. Additionally, solid headers have different shrinkage characteristics and are not the prescriptive solution referenced in CRC Table R602.7(1).
Option D: 2x10 double header
A double 2x10 exceeds the minimum requirement for a 6-foot opening with Douglas Fir-Larch in a single-story building. While it would work structurally, the CRC tables allow the smaller 2x8, making 2x10 a correct-but-oversized answer. The question asks for the minimum required size.
Memory Technique
For single-story Douglas Fir-Larch headers, remember the '6-foot = 2x8' rule as a baseline. Span increases by 2 feet roughly correlate to stepping up one lumber size: 6' = 2x8, 8' = 2x10, 10' = 2x12. This is a rough heuristic for single-story DF-L per CRC tables.
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