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Building Code Reference

Got a CRC R905.2 correction?

Asphalt shingle installation

For builders in California, Greater Seattle, the Las Vegas area, the Denver area and Kansas City · CrossBeam Permits

What this code requires, how to fix it, and how cities and counties review it

What this code requires

CRC R905.2 is the California Residential Code section that governs asphalt shingle installation on residential roofs. It sets the minimum slope at 2:12, specifies underlayment type and application method based on slope and wind zone, and requires fasteners that meet both the manufacturer's instructions and local wind uplift demands. Reroof and new-construction permits for single-family homes and ADUs are the most common permit types that trigger R905.2 corrections from plan-checkers.

How to fix it

  1. Confirm roof slope meets the 2:12 minimum for asphalt shingles

    Find the roof pitch callout on the site plan or roof framing plan and verify it is at least 2 units vertical in 12 units horizontal. If the design calls for anything under 2:12, asphalt shingles are not allowed and the spec must change to a code-compliant low-slope system. If the slope is borderline or the framing plan shows 2:12 but the drawing title says low-slope roof, add a note confirming which slope governs so the plan-checker does not have to resolve the conflict themselves. A clear slope dimension on the plan prevents a correction that could add weeks to the review cycle.

  2. Specify underlayment type and application method for your slope band

    R905.2 divides underlayment requirements by slope. For slopes 4:12 and steeper, one layer of ASTM D226 or D4869 felt or ASTM D8257 synthetic underlayment, lapped 2 inches, is the minimum. For slopes between 2:12 and 4:12, the code requires double underlayment: a half-width starter strip at the eave, then full-width sheets each lapped half a sheet plus 2 inches. Write the slope band and the application method explicitly on a roofing detail or spec note. Do not rely on a manufacturer reference alone without stating the number of layers and the overlap dimension for your slope.

  3. Add a fastening schedule showing nail gauge, head size, and sheathing penetration

    R905.2 requires fasteners that comply with both the manufacturer's code-listed installation instructions and the wind speed requirements from the structural drawings. At minimum, specify a 12-gauge roofing nail with a 3/8-inch-diameter head, long enough to penetrate the sheathing at least 3/4 inch. If the sheathing is thinner than 3/4 inch, the nail must pass all the way through. On the drawings, call out the nail size, head diameter, sheathing penetration, and number of nails per shingle. Projects in Wind Exposure Category C or D zones often require six fasteners per shingle instead of the standard four. Confirm this against the shingle product's evaluation report and call it out on the drawings.

  4. Check whether ice-and-water barrier is required for your climate zone

    California projects in areas subject to freeze-thaw cycles need a self-adhering polymer-modified bitumen sheet at the eave extending at least 24 inches inside the exterior wall line. It applies where the jurisdiction's CRC Table R301.2 designates a history of ice forming along the eaves. Coastal and inland-valley Southern California jobs typically do not trigger this requirement, but mountain-area ADUs and high-elevation reroofs frequently miss it. Check the jurisdiction's Table R301.2 design criteria before resubmitting. If the site is borderline, add the barrier. The material cost is small compared to the delay from a second correction.

  5. Tie the shingle product to its code-listed manufacturer installation instructions

    R905.2 defers many specifics to the manufacturer's installation instructions. On the drawings, list the shingle product name and manufacturer, and add a note: Install per manufacturer's code-listed installation instructions. Without this reference, the plan-checker cannot confirm that the product's performance assumptions match the code's minimum standards. Some jurisdictions also require the ICC ES evaluation report number on the plans. Ask the building department whether they want it, especially on reroof permits in cities with strict over-the-counter review.

  6. Show valley flashing type, material, and width on a roof plan detail

    R905.2.8.2 requires open metal valley linings at least 24 inches wide of a listed metal (for example 0.024-inch aluminum or 26-gauge G90 steel); closed valleys may use 36-inch smooth roll roofing or 36-inch ASTM D1970 membrane. Both open-valley and closed-cut valley methods are acceptable, but the method must be stated. A plan note reading flash as required does not pass. Add a valley detail or a note on the roof plan specifying the material, gauge, width, and installation method. If the roof plan does not clearly show valley locations, add them before resubmitting.

  7. Call out drip edge at eaves below underlayment and at rakes above underlayment

    R905.2 requires metal drip edge at both eaves and rakes, and the installation order differs by location. At the eave, the drip edge goes down first and the underlayment laps over it. At the rake, the underlayment goes down first and the drip edge laps over it. Getting the order wrong is a field rejection. On the drawings, add a note or detail that explicitly states metal drip edge at eave below underlayment and metal drip edge at rake above underlayment. Many correction letters for R905.2 cite the drip edge requirement solely because the callout is missing from the plans.

  8. Resubmit with revision clouds on every changed sheet

    When you send back the corrected plans, cloud every change and add a revision triangle with the revision number. If the plan-checker flagged a missing underlayment spec and you added it, cloud it so the reviewer finds it in under a minute. Resubmitting without revision clouds forces the reviewer to diff the entire set manually, which pushes your resubmit to the back of the queue. On a standard reroof permit, a complete and clearly marked R905.2 correction response typically turns around in one to three weeks, assuming no other open items on the same set.

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Why you got flagged

Plan-checkers flag R905.2 when the roofing specification on the permit drawings is incomplete or conflicts with what the code and the shingle manufacturer require for the roof slope and wind exposure on this project.

The single most common correction is a missing or vague underlayment callout. Many reroofing sets show the shingle product by name but never specify the underlayment beneath it. R905.2 requires at least one layer of underlayment on slopes 4:12 and above. On slopes between 2:12 and 4:12, the code requires double underlayment applied in a specific overlapping pattern, and drawings that simply say underlayment per manufacturer without calling out the double application method will get flagged. The inspector in the field cannot verify intent without it written down.

A second frequent citation is an incomplete fastening schedule. The plans might reference roofing nails but omit the shank gauge, head diameter, and required sheathing penetration depth. R905.2 ties fastener specs to both the manufacturer's installation instructions and the wind speed design values from the structural drawings. When those two pieces are not connected on the roofing sheet, the plan-checker marks it incomplete.

Low-slope shingle projects also trip this code when the specified slope barely clears 2:12 but the underlayment spec on the drawings is written for a steeper roof. The inspector checks the actual slope callout and compares it to the underlayment detail. A mismatch between slope and underlayment application method is a fast correction.

The official code

California Residential Code R905.2 - Asphalt Shingles, Building Standards Commission

Read the source →

Common questions

Does CRC R905.2 allow asphalt shingles on a 1.5:12 slope?
No. R905.2 sets a hard minimum of 2:12 for asphalt shingles. Anything below 2:12 requires a low-slope roofing system such as modified bitumen, built-up roofing, or a single-ply membrane. If you are pulling a reroof permit on an existing low-slope roof that currently has shingles, the jurisdiction will require you to change to a code-compliant low-slope system before they approve the permit.
What is the underlayment difference between a 3:12 slope and a 5:12 slope?
The dividing line is 4:12. For a 3:12 slope, you are in the low-slope zone under R905.2, which requires double underlayment: a half-width starter strip at the eave, then full-width sheets each lapped half a sheet plus 2 inches. At 5:12, a single layer is the minimum. The double-layer requirement adds material and labor, so it matters to get the slope callout right before you spec the underlayment. When the slope could land on either side of 4:12, spec for the low-slope condition to avoid a correction.
My reroof permit was flagged for fastening. What does the plan-checker actually need to see?
They want to see nail shank gauge, head diameter, and sheathing penetration depth written on the drawings. The R905.2 minimum is 12-gauge, 3/8-inch head, penetrating at least 3/4 inch into the sheathing. You also need to state the nail pattern per the shingle manufacturer's instructions. For most standard shingles that is four nails per shingle in the nailing zone, but products rated for high-wind zones often require six. If the structural drawings show Wind Exposure Category C or D, your fastening note must be consistent with it.
Do I need ice-and-water shield in Southern California under R905.2?
Most Southern California coastal and valley projects do not require it, because they are in climate zones that do not experience meaningful freeze-thaw cycles. The exception is where the jurisdiction's CRC Table R301.2 designates a history of ice forming along the eaves, typically mountain areas. There, R905.1.2 requires a self-adhering polymer-modified bitumen sheet at the eave extending at least 24 inches inside the exterior wall line. Check the jurisdiction's Table R301.2 design criteria. If the site is near a zone boundary or at elevation, add the barrier.
Can the plans just say install per manufacturer instructions for the shingles?
That note works as a supplement but not as the complete spec. You still need to identify the product by name and manufacturer, and you need to state the underlayment application method explicitly for your slope. The manufacturer reference alone does not tell the plan-checker or inspector what slope band governs or how many layers of underlayment to expect. A complete spec lists the product, references the manufacturer's code-listed installation instructions, and calls out the underlayment, fastening, and flashing details specific to the project.
Does R905.2 apply if I am adding a new layer over existing shingles?
Yes. R905.2 applies to overlay installations as well as full tear-offs. California allows one new layer over one existing layer when the existing layer is in acceptable condition and the total assembly does not create a weight or structural issue. The new layer must still meet all R905.2 requirements for underlayment, fastening, and flashing. If there are already two layers on the roof, both must come off before new shingles can go down. The permit drawings must clearly state whether this is a tear-off or overlay so the inspector knows what to look for.

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