When installing composition shingles on a roof with a 3:12 slope in California, what is the minimum required underlayment configuration per CRC Section 1507.2?
Correct Answer
C) Double layer of 15# felt with 19-inch overlap
CRC Section 1507.2.8 requires that for slopes between 2:12 and 4:12, composition shingles must have double underlayment consisting of two layers of underlayment cemented together or a base sheet with 19-inch side laps. This provides enhanced water protection for lower slope applications.
Why This Is the Correct Answer
CRC Section 1507.2.8 requires double underlayment for composition shingles installed on slopes between 2:12 and 4:12. The standard method is two layers of 15# felt with the first layer lapped 19 inches over the eave and each subsequent course overlapping by 19 inches (leaving a 17-inch exposure). This enhanced underlayment compensates for the slower drainage inherent in low-slope shingle applications.
Why the Other Options Are Wrong
Option A: Self-adhering polymer modified bitumen sheet
Self-adhering polymer modified bitumen (ice-and-water shield) is required at eaves in areas subject to ice damming, not as the general underlayment for a 3:12 slope throughout California. Using it for the entire roof would exceed the minimum requirement and significantly increase cost unnecessarily.
Option B: Single layer of 15# felt
A single layer of 15# felt meets the requirement only for slopes of 4:12 and above. A 3:12 slope falls in the low-slope range where a double layer is required. A single layer provides insufficient protection at this lower slope.
Option D: Ice barrier membrane covering entire roof
An ice barrier membrane covering the entire roof is required in specific cold-climate areas prone to ice damming, not universally in California for a 3:12 slope. California's climate generally does not require full-roof ice barrier membrane, and such a requirement would be excessive for most California locations.
Memory Technique
Below 4:12, double up. Think of a low slope as a slow lane — water moves lazily, so you need twice the protection. When the roof slope drops below 4:12, the underlayment count doubles.
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 calculating concrete volume for a rectangular footing that measures 8 feet by 12 feet by 2 feet deep, how many cubic yards of concrete are required?
Next Question
For wood structural panel shear walls in California Seismic Design Category D, what is the minimum nail penetration requirement into framing members when using 8d common nails?