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Building Code Reference

Got a CRC R806.1 correction?

Attic vent opening protection

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 R806.1 is the California Residential Code section that governs how attic ventilation openings must be covered and protected. Every opening in the attic ventilation system — whether soffit, gable, or ridge — must be covered with corrosion-resistant material. The mesh or covering must have openings sized to block rain, snow, and pests from getting into the attic. The code also controls the minimum and maximum mesh opening size. Most plan checkers flag R806.1 when the plans don’t call out the vent cover material, don’t specify mesh opening dimensions, or use a generic “vent per manufacturer” note without backing it up with compliant specs.

How to fix it

  1. Add a vent cover material callout to the exterior elevations

    On your exterior elevation sheets (typically A3 or A4), add a note calling out the attic vent cover type and material. State that covers are corrosion-resistant — anodized aluminum, stainless steel, or fiberglass mesh are the common choices. If you’re spec’ing a manufactured vent product, list the model number and confirm it meets R806.1 requirements. Don’t rely on a generic “attic vents per manufacturer” note; you need the actual product or material called out.

  2. Specify the mesh opening size on plans

    Your plans must show the mesh opening dimension for the vent covers. CRC R806.1 restricts mesh openings to prevent entry of rain, snow, and pests. The acceptable range in the current adopted code runs from 1/16 inch minimum up to 1/4 inch maximum for the typical pest-blocking screen. Some vent types (like corrosion-resistant wire cloth) are explicitly listed. Add a note or detail on the plans stating the mesh opening size in fractions of an inch, not just “fine mesh.” The plan-checker needs to be able to verify the opening dimension from the drawings alone.

  3. Confirm covers are corrosion-resistant for your climate zone

    The code word is “corrosion-resistant” — which cuts out plain steel, uncoated iron, and low-grade painted mesh. Galvanized steel is generally acceptable but check the gauge spec. Coastal projects (within about 1,000 feet of salt water) should use anodized aluminum or stainless steel since galvanized coatings deteriorate faster near the ocean. Call out the material explicitly on plans, not just by brand name, so the plan-checker can make the determination.

  4. Cross-reference R806.2 to confirm ventilation ratio

    R806.1 governs the cover material and mesh protection; R806.2 governs how much net free ventilation area is required. They’re linked: the mesh opening size you specify under R806.1 affects the net free area calculation. Once you fix the R806.1 callout, run the ventilation ratio under R806.2 using the actual net free area factor for your vent product. Manufacturers publish net free area ratings (in square inches per linear foot for continuous soffit vents, or total NFA for individual vents) — use those, not the gross vent opening, in your R806.2 calc.

  5. Include a vent detail for non-standard installations

    If your attic ventilation uses non-standard vent placement — like site-built pop-up ridge vents, built-up blocking with drilled holes, or vents cut into fascia boards — add a detail at 1/2 inch scale or larger showing the opening protection. Drilled holes in wood blocking, for example, need to be shown with a mesh insert or corrosion-resistant insect screen fitted over them. The detail doesn’t need to be elaborate, but it has to demonstrate that the vent opening is protected per R806.1.

  6. For existing vents on permit scope, document compliance in the plans

    If your project is a re-roof, attic insulation job, or attic conversion and you’re not changing the vents, you still need to address R806.1 if the plan-checker flagged it. Add a general note stating: “Existing attic ventilation openings to be verified in field to comply with CRC R806.1. Non-compliant covers to be replaced with corrosion-resistant covers with maximum 1/4-inch mesh openings prior to final inspection.” This shifts the verification to the field inspection and closes the plan-check comment without requiring a full vent redesign at the drawing stage.

  7. Resubmit with a response letter calling out each R806.1 change

    When you resubmit, include a written response to the plan-checker’s comment that points to the exact sheet and detail where you addressed R806.1. Something like: “R806.1 — Attic vent cover material and mesh opening size added to Elevation Sheet A3, Note 5. Corrosion-resistant anodized aluminum covers with 1/8-inch mesh openings per manufacturer model XYZ.” Plan-checkers review dozens of resubmittals at once; making it easy to find your fix speeds up the review cycle.

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Why you got flagged

Here’s why plan-checkers flag R806.1 in corrections letters.

The most common trigger is a missing callout. Plans show soffit or gable vents on the elevations but never specify the cover material or mesh opening size. A plan-checker scanning for R806.1 compliance will circle that callout and send it back. The drawings have to say the covers are corrosion-resistant and show the mesh dimension. Noting “attic vents per manufacturer” doesn’t cut it unless the manufacturer’s spec sheet is on the plan set and the plan-checker can verify it meets the mesh size requirement.

The second scenario is mesh that’s too coarse. R806.1 sets a maximum opening size to prevent pest entry. Birds, bats, and rodents can squeeze through openings that look small on a product sheet. If your vent spec has a mesh opening larger than the maximum allowed (typically 1/4 inch for the fine pest screen), the plan-checker will flag it. Mesh that’s too fine causes a different problem: undersized openings restrict airflow and can prevent the vent from meeting the required ventilation ratio under R806.2.

A third situation comes up on re-roofs and attic conversions. Existing vents are in place, but the permit scope touches the roof assembly and the plan-checker now has to confirm the existing vents comply with current code. If the existing hardware isn’t documented and shown to meet R806.1’s material and opening requirements, it comes back as a correction even on work that wasn’t changing the vents at all.

Finally, corrosion resistance is its own failure mode. Plans sometimes spec painted steel mesh near coastal areas, which rusts out quickly, or aluminum screen that’s too thin and prone to tearing. The code requires corrosion-resistant material, and coastal jurisdictions sometimes read that requirement stricter than inland cities.

The official code

California Residential Code R806.1 — Attic Ventilation Opening Protection (CA Building Standards Commission)

Read the source →

Common questions

Does CRC R806.1 apply to re-roofs or only new construction?
R806.1 can get flagged on re-roofs. When a re-roof permit covers the full roof assembly or changes the roof deck, the plan-checker has the authority to require confirmation that existing attic ventilation openings comply with current code. If your plans don’t address the existing vents, expect a correction. The cleanest fix is a note on the plans stating that existing vents will be field-verified and any non-compliant covers replaced before final inspection.
What mesh size does CRC R806.1 require for attic vent covers?
The current adopted California Residential Code specifies a range for mesh opening size. The maximum opening is 1/4 inch — anything larger lets rodents and birds through. The minimum opening (typically 1/16 inch) prevents the mesh from becoming so fine that it restricts airflow. Wire cloth, hardware cloth, and corrosion-resistant insect screen are all listed as acceptable cover types in R806.1. The specific product you spec needs to fall within that opening range, and the plan must state the mesh dimension, not just the brand name.
Can I use galvanized steel mesh for attic vent covers in California?
Yes, galvanized steel is generally listed as a corrosion-resistant material under CRC R806.1. The catch is location. Coastal areas, particularly within 1,000 feet of salt water, see galvanized coatings fail faster than inland. Some coastal jurisdictions interpret the corrosion-resistance requirement stricter and ask for stainless or anodized aluminum near the ocean. Confirm with your local building department if the project is in a coastal zone. For inland residential work, galvanized mesh at the right opening size is a standard, code-compliant choice.
What's the difference between CRC R806.1 and R806.2?
R806.1 covers the physical protection of the vent openings: what the covers are made of (corrosion-resistant material) and how the openings are sized (mesh dimension to keep out pests and water). R806.2 covers the quantity of ventilation: the net free area ratio relative to the floor area of the space being ventilated. Both sections need to be addressed when attic ventilation is on the plan-check scope. Fixing R806.1 without checking R806.2 is a common way to get a second corrections letter.
Do I need a detail drawing to satisfy R806.1 or is a note enough?
A well-written note is usually sufficient for standard manufactured vents. The note needs to state the vent cover material (corrosion-resistant), mesh opening size, and product model or spec. If you’re using a non-standard installation like field-built openings in wood blocking or a site-built ridge cap with cut slots, add a detail at 1/2 inch scale or larger showing how the opening is protected. Plan-checkers flag R806.1 when they can’t confirm mesh compliance from the drawings, so the test is: can the plan-checker verify the opening protection without calling you? If yes, you’re good. If not, add a detail.
My plans already show attic vents — why did I still get an R806.1 correction?
Showing vents on the elevation is not the same as specifying R806.1-compliant covers. The elevation might show a vent symbol at the gable or a continuous soffit vent at the eave, but unless the callout specifically addresses corrosion-resistant covers and mesh opening size, the plan-checker can’t verify compliance. The fix is to add a specific note or detail, not just the vent symbol. Check if your plans say anything about vent cover material or mesh dimension. If the only note is “attic vents per manufacturer” or there’s no note at all, that’s why you got flagged.

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