CSLB General Building (B)Finishes and Building EnvelopeHard
A contractor is installing a curb-mounted skylight on a composition shingle roof. Per code requirements for skylight curb construction, what is the minimum height the curb must extend above the plane of the roofing material?
- A6 inches
- B2 inches
- C8 inches
- D4 inches
Show answer & explanationAnswer & explanation
Correct answer: D. 4 inches
Code requires that skylight curbs extend a minimum of 4 inches above the plane of the roofing surface, matching the general minimum flashing height requirement used for roof penetrations. This height helps ensure that water and debris flowing across the roof surface do not reach the skylight seal or glazing unit.
Why the other options are wrong
- A. 6 inches exceeds the code minimum, though not incorrect practice, it is not the required minimum.
- B. 2 inches is insufficient and does not meet the minimum curb height requirement.
- C. 8 inches is well above the minimum and not the code-specified value.
Skylight Curb Height
Skylight curbs must extend a minimum of 4 inches above the roofing plane to keep water and debris away from the unit's seals and glazing.
- Minimum curb height is 4 inches above roofing surface
- Applies to curb-mounted skylight installations
- Flashing must integrate with roofing underlayment and shingles around the curb
Memory trick: 'Four inches keeps water off the glass' — same 4-inch rule as other roof penetrations.