Reroof (Roof sheathing) | Building Code Requirements

”Reroof” It’s the process of recovering or replacing an existing roof covering according to California residential code.

Does reroof (roof sheathing) require a building permit?

The answer is yes, Local jurisdictions (cities & counties) are requiring a building permit to install a new roof or/and adding a second layer on top of an existing layer.

How many inspections are needed to finalize the roofing permit?

The local jurisdictions will require two or three inspections to finalize the reroofing permit. They are pre-inspection, plywood & nailing, and Final inspection after all work has been completed. (R109.1.5).

Ladder/access and fall protection equipment meeting minimum safety standards must be provided. The contractor or the homeowner are responsible for securing and setting up the ladder prior inspection. (R109.3).

Who can apply for a Reroof permit?

Per CSLB a C-39 – roofing Contractor or a B – General Building Contractor. However, if the homeowner is doing the work himself/herself, the local jurisdictions will allow him/her to obtain the roofing permit.

Reroof over an existing roofing material

The California residential building code allow adding only a second layer over an existing single roof layer, It is not permitted if one or more of the following conditions exist (R908.3.1.1),

  • The existing roofing is water damaged or has deteriorated to the point that the existing roof or roof covering is not strong enough to support an additional roofing.
  • Where the existing roof covering is wood shake, slate, clay, or cement tile. see exceptions below.
  • Where the existing roof has 2 or more roof layers.


Where the application of a new roof covering over wood shingle or shake roofs creates a combustible concealed space, the entire existing surface shall be covered with gypsum board, mineral fiber, glass fiber or other approved materials securely fastened in place. (R908.4).

If any of the previous conditions existed, the existing roof covering (materials) shall be removed completely and install new application (roofing materials).

Existing roof materials

Existing slate, clay or cement tile shall be permitted for reinstallation, except if it is damaged, cracked or broken slate or tile shall not be reinstalled. (R908.5).

Roof Covering slope Code Requirements

The California residential code specify a minimum roof slope for all roof covering materials, so before deciding on the roof material please see below,

  • Minimum 2 in 12 for asphalt shingles(R905.2).. Roof slopes between 2 in 12 and up to 4 in 12 require double roof underlayment. Table R905.1.1(1)(2)(3).
  • Minimum 2 ½ in 12 for clay and concrete tiles. Roof slopes between 2 ½ and 12 and up to 4 in 12 require double underlayment.(R905.3).
  • Minimum 3 in 12 for metal roof shingles (R905.4).
  • Minimum 1 in 12 for mineral surfaced rolled roofing. (R905.5).
  • Minimum 4 in 12 for slate and slate-type shingles. (R905.6).
  • Minimum 3 in 12 for wood shingles. (R905.7).
  • Minimum 3 in 12 for wood shakes.(R905.8).
  • Minimum ¼ in 12 for built up roofing.(R905.9).
  • Minimum 3 in 12 for lapped non soldered non sealed metal roof panels (R905.10).
  • Minimum ¼ in 12 for standing-seam roof systems.(R905.10).
  • Minimum ¼ in 12 for modified bitumen roofing. (R905.11).

Roof and attic ventilation

The minimum ventilating area shall be 1/150 of the area of the vented space (1 square foot for each 150 square feet of the roof area)(R806.2.).
Exception: The minimum ventilation area shall be reduced to 1/300 of the vented space provided if the following condition exists,

When 40% and not more than 50% of openings are in the upper portion no more than 3 ft. below the ridge or highest point of the space.

Low profile roof dormer ''O'hagin''

Plywood or Oriented Strand Board Sheathing (OSB)

For existing deck (roof sheathing) make sure to replace any damaged, broken, and deteriorated wood.

Sheathing exposed to weather (underside of eaves) must have exterior grade glue (marked as “Exterior” or “Exposure 1”). (R803.2.1.1). If not make sure the exposed plywood are primed.

Roof sheathing inspection
Replacing damaged existing wood before roof sheathing inspection

Roof Sheathing Thickness

7/16” OSB with a span rating of 24/16 is used as the minimum plywood thickness for the roof sheathing and will not require clips. (Table R503.2.1.1(1)).

Minimum nailing is 8d common nails at 6” on center at supported edges and 12” on center in the field. 6” on center for boundaries nails. (Table R602.3 (1)).

Boundaries nails goes on top of the blocking of the exterior walls.

Reference Code – International Residential Code – California Residential code