CSLB C-39 Roofing Contractor

Building code requires a double layer of underlayment on low-slope asphalt shingle roofs (2:12 to under 4:12) to compensate for slower water runoff.

• Asphalt shingles require minimum 2:12 slope
• 2:12 to <4:12 requires double underlayment application
• 4:12 and above only requires standard single-layer underlayment

Skylight flashing is installed shingle-fashion: apron (bottom) first, step flashing up the sides, and head flashing last at the top under upslope shingles.

• Apron flashing = bottom, installed first
• Step flashing = sides, interwoven with shingles
• Head flashing = top, installed last, under upslope shingles

Pipe flashing boot quantities are calculated by counting penetrations, adding a waste/spare allowance, then dividing by the pack size sold.

• Add a spare percentage before dividing by pack size.
• Always round up both the boot count and the pack count.
• Pack sizes vary by manufacturer, commonly sold in sets of 6.

Built-up roofing requires interply asphalt moppings, typically applied around 20-25 lb per square, and total asphalt needed scales with area and number of moppings.

• 1 square = 100 sq ft
• Total lbs = rate × squares × number of moppings
• Standard interply rate: ~20-25 lb/square

Hip and valley rafters are longer than common rafters for the same run because they travel diagonally in three dimensions; rafter tables provide a per-foot-of-run factor to calculate their true length.

• Hip/valley factor is always greater than the common rafter factor for the same pitch
• Multiply common rafter run by the hip factor to get length in inches
• Divide by 12 to convert the result to feet

Ridge cap material quantities are determined by summing all ridge and hip linear footage, applying a waste factor, then dividing by bundle coverage.

• Add ridge length plus all hip lengths together
• Apply standard waste factor (commonly 10%)
• Divide total adjusted footage by bundle coverage and round up

Underlayment rolls are rated for net coverage after overlap; waste factors must be added to account for laps, valleys, and cutting.

• Coverage is stated per roll after overlap allowance
• Apply 10% waste factor as standard estimating practice
• Always round rolls up to whole units

Labor hours for a roofing job are estimated by dividing the total roofing squares by the crew's installation production rate per hour.

• Labor hours = total squares ÷ squares installed per hour.
• Production rates vary by roof complexity and crew size.
• Estimators often add buffer time for tear-off, cleanup, and complexity.

A valley design where metal flashing is exposed and shingles are trimmed back on both sides to create a clear water channel.

• Metal channel widens toward the eave
• Shingle corners clipped and sealed with cement
• No nails placed within the exposed metal area

When calculating linear roll coverage with end-lap overlaps, subtract the overlap distance from the roll length to find effective coverage, then divide the total run by that effective length.

• Effective coverage = roll length minus overlap
• Always round up partial rolls to full rolls
• Applies to valley membranes, ice barriers, and similar linear runs

Step flashing pieces must rise at least 4 inches up the sidewall and lap the previous piece by at least 2 inches to prevent water bypass.

• Installed with each course of shingles, not as one long strip.
• Minimum 4-inch wall leg per code.
• Minimum 2-inch overlap between successive pieces.

A roofing square is a unit of measure equal to 100 square feet of roof surface, used to standardize material takeoff.

• 1 square = 100 sq ft
• Always divide total area by 100 to find squares
• Round up to the next whole square when ordering

The minimum height (4 inches) that a roof drain strainer dome must extend above the adjacent roof surface per the California Plumbing Code, to prevent debris blockage.

• CPC requires minimum 4-inch strainer height
• Prevents leaves/debris from clogging the drain
• Applies to primary roof drains on low-slope roofs

Tapered insulation boards are manufactured to create a designed slope toward drains by increasing thickness at a fixed rate per foot of horizontal run.

• Rise = slope rate (in/ft) × horizontal distance (ft)
• Final thickness = starting thickness + total rise
• Common taper rates are 1/8, 1/4, and 1/2 inch per foot

PVC membranes contain plasticizers that migrate when in contact with asphalt products, causing membrane embrittlement and failure.

• Requires separator sheet or cover board
• Common issue in re-roofing over BUR/mod bit
• Manufacturers specify compatible barriers

Total gable roof area is found by computing the sloped rafter length from the run and slope factor, then multiplying by building length and doubling for both roof planes.

• Run to ridge equals half the building width.
• Rafter length = run × slope factor from a rafter table.
• Multiply rafter length by building length, then double for two planes.

Fiberglass batt R-values are based on installation at full designed thickness; compressing batts into shallower cavities reduces trapped air and lowers effective R-value.

• R-value depends on trapped air volume
• Compressed batts underperform their rating
• R-19 compressed to 3.5" often performs near R-13

Combining gable vents with a ridge vent system can cause air to bypass the soffit-to-ridge airflow path, reducing overall attic ventilation effectiveness.

• Air takes the path of least resistance
• Nearby gable vent can short-circuit ridge vent draw
• Best practice: use one consistent exhaust/intake system

A multiplier from a standard roof area factor table converts a flat plan (footprint) area into actual sloped roof surface area for a given slope and roof type.

• Multiply footprint area by the slope's area factor.
• Factors are typically found in rafter/area tables by slope ratio.
• Convert final square footage to roofing squares by dividing by 100.

The total weight of loose ballast (typically river rock) required on a ballasted single-ply roof, calculated by multiplying roof area by the code-required ballast rate per square foot.

• Common minimum rate: 10 lb/sq ft in low wind zones
• Higher wind exposure zones require heavier ballast rates
• 1 ton = 2,000 lb

The portion of a shingle left uncovered (visible) after installation, which determines headlap coverage.

• Standard 3-tab shingle: 12in x 36in, 5in exposure
• Exposure + headlap = shingle length minus overlap
• Manufacturer specs always govern actual exposure

Applying closed-cell spray foam directly to roof sheathing creates a sealed, conditioned attic that becomes part of the building envelope, eliminating the need for soffit/ridge ventilation.

• Foam applied directly to underside of roof deck
• Attic becomes part of conditioned space
• Standard 1/150 or 1/300 ventilation not required

A contact adhesive used to bond EPDM seams that must partially dry (flash off) to a tacky, non-stringy state before the two coated surfaces are pressed together.

• Contact adhesives bond best when tacky, not wet or fully dry
• Test by touching with a dry finger — no strings or transfer means ready
• Roll the seam after bonding to ensure full contact

Drip edge quantities are calculated from total eave and rake footage plus a waste allowance, then divided by stock piece length and rounded up.

• Combine eave and rake linear footage
• Apply standard waste percentage (commonly 5%)
• Round the final piece count up to the next whole piece