When installing floor joists in California residential construction, what is the maximum allowable deflection under live load according to the CRC?
Correct Answer
D) L/360
CRC Section R301.7 and Table R301.7 specify that floor joists must not deflect more than L/360 under live load, where L is the span length. This stringent requirement ensures adequate stiffness for floor systems and prevents excessive deflection that could cause cracking in finishes or structural issues.
Why This Is the Correct Answer
CRC Section R301.7 and Table R301.7 establish L/360 as the maximum allowable live load deflection for floor joists. The L/360 limit ensures floors are stiff enough to avoid bounce, cracking of finishes, and occupant discomfort. For a 15-foot span, this allows just 1/2 inch of deflection under live load.
Why the Other Options Are Wrong
Option A: L/300
L/300 is less stringent than the code requirement for floors. It is sometimes used for roof members but does not meet the stricter floor standard of L/360. Applying L/300 to floors would allow too much deflection.
Option B: L/180
L/180 is the least restrictive value and applies to roof rafters supporting no finished ceiling. It is far too lenient for floor systems and would result in an unacceptably bouncy floor.
Option C: L/240
L/240 applies to roof rafters with finished ceiling or some wall assemblies. It is more restrictive than L/180 but still not as strict as the L/360 required for floor joists under live load.
Memory Technique
Use the mnemonic 'Floors need more, so 360.' The higher the denominator, the smaller the allowed deflection — floors require the greatest stiffness, so they get the highest denominator (360). Think: 'Floors = 360 degrees = full circle of stiffness.'
More trade-general-building Questions
When installing engineered lumber joists (I-joists) in California residential construction, what is the primary code requirement for web stiffeners?
What is the required attic ventilation ratio when a vapor retarder is installed on the warm-in-winter side of the ceiling according to the California Residential Code?
In California's Wildland-Urban Interface (WUI) areas, which underlayment requirement applies to Class A fire-rated roof assemblies?
In California, when installing a tankless water heater in a seismic zone, what additional requirement must be met beyond standard installation practices?
According to the California Building Code (CBC), what is the minimum lap splice length for #4 rebar in a concrete foundation wall in normal weight concrete with f'c = 3000 psi?
According to CBC requirements for retaining walls in California, what additional design consideration must be addressed for retaining walls over 4 feet in height located in seismic design categories D, E, and F?
When constructing retaining walls in California that exceed 4 feet in height, which CBC requirement must be met regarding drainage?
Under California regulations, when is a reduced pressure principle (RPP) backflow prevention assembly required for a residential water service connection?
Under California Title 24, what is the minimum electrical service size required for new single-family residential construction?
According to the California Building Code, buildings located in Seismic Design Category D must comply with which specific seismic design requirements?
People Also Study
Business & Financial Management
120 questions · 70% to pass
Contract Administration
60 questions · 70% to pass
Project Management
60 questions · 70% to pass
Related Study Resources
Previous Question
When placing concrete in hot weather conditions per CBC Section 1906.12, what is the maximum concrete temperature allowed at the time of placement in California?
Next Question
According to the California Residential Code, what is the maximum horizontal distance allowed between a fixture trap and its vent connection for a 1.5-inch drain pipe?