CBC · California Building Code
What underlayment and ice-barrier requirements apply to different roof coverings?
The CBC requires underlayment types and installation methods shown in Table 1507.1.1(1) (see § 1507.1.1) and, in areas with a history of eave ice, an ice barrier (two layers cemented together or a self‑adhering ASTM D1970 membrane) extending 24 inches inside the exterior wall line (§ 1507.1.2). Check the specific roof‑covering section along with Table 1507.1.1(1) for slope, wind‑speed fastening, and material options before specifying underlayment .
Last reviewed: July 5, 2026
What the code requires — 2-4 sentences
The California Building Code requires an approved underlayment be installed under roof coverings in the manner and type shown in Table 1507.1.1(1) and described in § 1507.1.1; where there is a history of ice forming on eaves, an ice barrier (two layers of underlayment cemented together or a self‑adhering polymer‑modified bitumen membrane) must be installed and extend at least 24 inches inside the exterior wall line (§ 1507.1.2). Specific roof-covering sections (asphalt, tile, metal, slate, wood, roll roofing, BIPV, etc.) reference § 1507.1.1 for the underlayment method and list additional slope or fastening rules (see Table 1507.1.1(1) and associated sections) .
Requirements in detail
Key rule sources (CBC)
- Underlayment types, layering and fastening methods are specified by § 1507.1.1 and Table 1507.1.1(1) (underlayment application and fastener requirements) .
- Ice-barrier (also called ice-and‑water barrier) trigger, composition and extent are in § 1507.1.2 (two layers cemented together or self‑adhering ASTM D1970 membrane; extend 24 inches inside exterior wall) .
- Individual roof-covering sections (e.g., asphalt § 1507.2, tile § 1507.3, metal § 1507.4/1507.5, roll roofing § 1507.6, slate § 1507.7, wood §§ 1507.8–1507.9, BIPV § 1507.17) refer back to § 1507.1.1 for underlayment and § 1507.1.2 for ice barrier where applicable .
How to read the decision dimensions
The two primary decision dimensions are:
- Roof covering type (asphalt shingles, clay/concrete tile, metal panels/shingles, roll roofing, slate, wood shingles/shakes, BIPV).
- Climate / exposure conditions that affect the underlayment choice: slope range, basic wind speed, and whether the location is an ice‑forming (freeze) area that triggers an ice barrier.
Below is a concise decision table synthesizing the application options shown in Table 1507.1.1(1) and the ice‑barrier rule in § 1507.1.2.
| Roof covering | Typical underlayment options / application (decision‑relevant) | When double underlayment or special application is required | Ice barrier required? | Code Reference |
|---|---|---|---|---|
| Asphalt shingles | Comply with Table 1507.1.1(1): options include (A) two layers of mechanically fastened felt applied per the table; (B) 4" self‑adhering strips over decking joints plus approved underlayment over roof; or (C) single layer of self‑adhering ASTM D1970 membrane installed per manufacturer | Double underlayment specifically required for slopes from 2:12 up to 4:12 for asphalt (§ 1507.2.2) | Yes — where there is a history of ice forming on the eaves (§ 1507.1.2) | § 1507.1.1, Table 1507.1.1(1); § 1507.2; § 1507.1.2 |
| Clay & concrete tile | Table options include: (1) for 2½:12–4:12, two layers applied by the method in the table; (2) for ≥4:12 a single layer shingle‑fashion; or (3) single layer ASTM D1970 self‑adhering membrane | Lower slopes (2½:12–4:12) require two layers per the table; alternative mechanized/self‑adhering methods permitted for joints/transition areas | Yes for tile types listed in § 1507.1.2 (ice‑area trigger applies to slate and similar; code references show ice‑barrier rules apply to tile types where listed in individual sections) | § 1507.3; Table 1507.1.1(1); § 1507.1.2 |
| Metal roof panels / metal roof shingles | Underlayment per § 1507.4 / § 1507.5 and Table 1507.1.1(1); self‑adhering ASTM D1970 allowed as alternative in many cases; follow manufacturer’s instructions for deck and exposure | Some metal coverings require full‑coverage underlayment or specific fastening at higher wind speeds (see table columns for V <130 mph vs V ≥130 mph) | Where listed (metal roof shingles are listed in § 1507.1.2), ice barrier applies in ice history areas | § 1507.4–1507.5; Table 1507.1.1(1); § 1507.1.2 |
| Mineral‑surfaced roll roofing | Underlayment per § 1507.6 and Table 1507.1.1(1) | Minimum slope limitations and method in § 1507.6; follow table for wind speed‑based fastening | Yes where required by § 1507.1.2 (ice areas) | § 1507.6; Table 1507.1.1(1); § 1507.1.2 |
| Slate, wood shingles, wood shakes | Underlayment must comply with § 1507.1.1; specific application details and slope minimums are in §§ 1507.7–1507.9 | Slate/wood sections impose slope minimums and application detail; consult the roof‑type section together with Table 1507.1.1(1) | Yes — slate and wood shingles/shakes are explicitly listed in § 1507.1.2 as ice‑barrier subjects | §§ 1507.7–1507.9; Table 1507.1.1(1); § 1507.1.2 |
| BIPV roof coverings | Underlayment options mirror Table 1507.1.1(1); for certain slopes two layers are required (see § 1507.17 and table) | Slope‑based two layer requirement for 3:12–4:12 and single for ≥4:12 (see BIPV sub‑section) | Ice barrier required where ice history exists (per § 1507.1.2); exceptions for detached unconditioned accessory structures | § 1507.16/1507.17; Table 1507.1.1(1); § 1507.1.2 |
Notes on wind speed and fastening: Table 1507.1.1(1) and the companion fastener table distinguish application and fastening when the maximum basic wind speed (V) is below certain thresholds (e.g., V < 130 mph) versus higher thresholds (V ≥ 130 mph). At higher wind speeds mechanically fastened underlayment and specific cap‑nail/cap‑staple requirements are mandated (see table and the underlayment fastening details) .
Underlayment application options (summary from Table 1507.1.1(1))
The common, code‑allowed underlayment solutions shown in the table are:
- Two layers of mechanically‑fastened underlayment applied with prescribed overlaps and fastening pattern (typical for lower slopes or specific coverings).
- A strip (4 inches) of self‑adhering polymer‑modified bitumen over decking joints plus the approved underlayment over the roof.
- A single layer of self‑adhering polymer‑modified bitumen underlayment complying with ASTM D1970 installed per manufacturer instructions.
These options are repeated across many roof‑covering entries in Table 1507.1.1(1) and are subject to wind‑speed and slope conditions in the table text .
Exceptions & special cases
- Detached accessory structures that do not contain conditioned floor area are excepted from the ice‑barrier requirement in § 1507.1.2 .
- The code permits the use of ASTM D1970 self‑adhering underlayment as an alternative in many cases (including as a single‑layer solution), but manufacturers’ installation instructions and deck/ventilation/climate exposure provisions must be followed; some coverings (e.g., wood shingles/shakes) have explicit exceptions to self‑adhering usage in the Residential Code — verify the specific roof‑covering section for prohibitions or limitations .
- Reroofing: where an existing adhered ice barrier or self‑adhering underlayment is present and the decking is sound, the code allows limited exceptions for leaving the existing membrane in place and covering with a new layer under certain conditions — see § 1512.2 exceptions (reroofing) for the CBC rerofing rules .
Common mistakes
- Assuming “one size fits all” underlayment: many roof coverings have slope‑specific or covering‑specific underlayment rules; always check the specific § and Table 1507.1.1(1) entry for that covering (§ 1507.1.1 / Table 1507.1.1(1)) .
- Forgetting the ice‑area trigger: ice barriers are not required everywhere — they are required where there is a history of ice forming on eaves; the code sets the requirement and the extent (24 inches inside exterior wall) in § 1507.1.2 .
- Using self‑adhering membranes improperly: ASTM D1970 membranes are permitted alternatives, but they must be installed per the membrane and roof‑covering manufacturers for deck material, ventilation and climate exposure; for some roof coverings (see covering sections) the code or residential provisions restrict their use .
- Overlooking wind‑speed fastening differences: Table 1507.1.1(1) and the underlayment‑fastening tables change fastening patterns in higher basic wind speed regions — failing to adopt the more robust fastening for V ≥ threshold can violate the code .
Worked example — concrete scenario
Scenario: You are reroofing a house in a California mountain town that is in an area with occasional eave icing. The roof is to receive asphalt strip shingles on a 3:12 slope, and the basic wind speed for the site is 100 mph (V < 130 mph).
Code application:
- Slope effect: For asphalt shingles between 2:12 and 4:12, the CBC (§ 1507.2.2) requires double underlayment application; therefore you must apply two layers per the method in § 1507.1.1/Table 1507.1.1(1) (for example, two layers of mechanically fastened felt with the specified overlaps) .
- Ice barrier effect: Because the location has a history of ice forming along the eaves, an ice barrier is required. Per § 1507.1.2, install either (A) not fewer than two layers of underlayment cemented together running from the lowest edge of all roof surfaces to at least 24 inches inside the exterior wall line, or (B) a self‑adhering polymer‑modified bitumen sheet in lieu of normal underlayment, extending 24 inches inside the exterior wall line. Detached accessory exceptions do not apply here if the house is conditioned living space .
- Wind speed: With V = 100 mph (<130 mph), use the Table 1507.1.1(1) application requirements for V < 130 mph (mechanical fastening sufficient to hold in place, as described for the lower wind category). If the site had V ≥ 130 mph, stricter mechanical‑fastening details (grid pattern, cap nails, annular ring nails, etc.) in the underlayment fastening table would apply .
Practical outcome: Install the required two layers of underlayment per the table, and either make those two layers cemented together for the ice barrier area (from eave to 24" inside wall) or install an ASTM D1970 self‑adhering membrane over the same zone and follow manufacturer instructions for the rest of the roof underlayment per Table 1507.1.1(1) .
Related provisions
- § 1507.1.1 — Underlayment requirements and Table 1507.1.1 series (underlayment application and fastening) .
- § 1507.1.2 — Ice barriers: when required, composition and required extent (24 inches) .
- § 1507.2 — Asphalt shingles (slope and double‑underlayment trigger) .
- § 1507.3 — Clay and concrete tiles (underlayment options and slope rules) .
- § 1507.4 / § 1507.5 — Metal roof panels and metal roof shingles (underlayment and ice barrier cross‑references) .
- § 1507.6 — Mineral‑surfaced roll roofing (underlayment/ice barrier references) .
- § 1512.2 — Reroofing exceptions regarding existing ice barriers and self‑adhered underlayment conditions (leave‑in‑place rules) .
Code references
Grounded in the retrieved California Building Code — click a citation to read the verbatim passage:
CBC § 1507.4.5 High relevance — show source text
1507.4.5 Underlayment and high wind. Underlayment shall comply with Section 1507.1.1.
1507.5 Metal roof shingles. The installation of metal roof shingles shall comply with the provisions of this section.
1507.5.1 Deck requirements. Metal roof shingles shall be applied to a solid or closely fitted deck, except where the roof covering is specifically designed to be applied to spaced sheathing.
1507.5.2 Deck slope. Metal roof shingles shall not be installed on roof slopes below 3 units vertical in 12 units horizontal (25percent slope).
1507.5.3 Underlayment. Underlayment shall comply with Section 1507.1.1.
1507.5.4 Ice barrier. Where required, ice barriers shall comply with Section 1507.1.2.
1507.5.5 Material standards. Metal roof shingle roof coverings shall comply with Table 1507.4.3.
1507.5.6 Attachment. Metal roof shingles shall be secured to the roof in accordance with the approved manufacturer’s installation instructions.
1507.5.7 Flashing. Roof valley flashing shall be of corrosion-resistant metal of the same material as the roof covering or shall comply with the standards in Table 1507.4.3. The valley flashing shall extend not less than 8 inches (203 mm) from the centerline each way and shall have a splash diverter rib not less than [3] / 4 inch (19.1 mm) high at the flow line formed as part of the flashing. Sections of flashing shall have an end lap of not less than 4 inches (102 mm). In areas where the average daily temperature in January is 25°F (-4°C) or less or where there is a possibility of ice forming along the eaves causing a backup of water, the metal valley flashing shall have a 36-inch-wide (914 mm) underlayment directly under it consisting of either one layer of underlayment running the full length of the valley or a self-adhering polymer-modified bitumen sheet bearing a label indicating compliance with ASTM D1970, in addition to underlayment required for metal roof shingles. The metal valley flashing underlayment shall be solidly cemented to the roofing underlayment for roof slopes under seven units vertical in 12 units horizontal (58-percent slope) or selfadhering polymer-modified bitumen sheet shall be installed.
1507.6 Mineral-surfaced roll roofing. The installation of mineral-surfaced roll roofing shall comply with this section.
1507.6.1 Deck requirements. Mineral-surfaced roll roofing shall be fastened to solidly sheathed roofs.
1507.6.2 Deck slope. Mineral-surfaced roll roofing shall not be applied on roof slopes below 1 unit vertical in 12 units horizontal (8-percent slope).
1507.6.3 Underlayment. Underlayment shall comply with Section 1507.1.1.
1507.6.4 Ice barrier. Where required, ice barriers shall comply with Section 1507.1.2.
1507.6.5 Material standards. Mineral-surfaced roll roofing shall conform to ASTM D3909 or ASTM D6380.
1507.7 Slate shingles. The installation of slate shingles shall comply with the provisions of this section.
1507.7.1 Deck requirements. Slate shingles shall be fastened to solidly sheathed roofs.
CBC § 1507.1.1 High relevance — show source text
Fasteners shall be applied along the overlap at not more than 36 inches (914 mm) on center. Underlayment installed where V asd is not less than 120 mph (54 m/s) shall comply with ASTM D226, Type III, ASTM D4869, Type IV or ASTM D6757. The underlayment shall be attached in a grid pattern of 12 inches (305 mm) between side laps with a 6-inch (152 mm) spacing at the side laps. The underlayment shall be applied in accordance with Section 1507.1.1 except all laps shall be not less than 4 inches (102 mm). Underlayment shall be attached using cap nails or cap staples. Caps shall be metal or plastic with a nominal head diameter of not less than 1 inch (25.4 mm). Metal caps shall have a thickness of not less than 0.010 inch (0.25 mm). Power-driven metal caps shall have a thickness of not less than 0.010 inch (0.25 mm). Thickness of the outside edge of plastic caps shall be not less than 0.035 inch (0.89 mm). The cap nail shank shall be not less than 0.083 inch (2.11 mm) for ring shank cap nails and 0.091 inch (2.31 mm) for smooth shank cap nails. Staple gage shall be not less than 21 gage [0.0.2 inch (0.81 mm)]. Cap nail shank and cap staple legs shall have a length sufficient to penetrate through-the-roof sheathing or not less than [3] / 4 inch (19.1 mm) into the roof sheathing.
Exception: As an alternative, adhered underlayment complying with ASTM D1970 shall be permitted.
1507.17.4.2 Ice barrier. In areas where there has been a history of ice forming along the eaves causing a back-up of water, an ice barrier consisting of not fewer than two layers of underlayment cemented together or of a self-adhering polymer modified bitumen sheet shall be used instead of normal underlayment and extend from the lowest edges of all roof surfaces to a point not less than 24 inches (610 mm) inside the exterior wall line of the building.
Exception: Detached accessory structures that do not contain conditioned floor area.
1507.17.5 Material standards. BIPV roof panels shall be listed and labeled in accordance with UL 7103.
1507.17.6 Attachment. BIPV roof panels shall be attached in accordance with the manufacturer’s installation instructions.
1507.17.7 Flashing. Flashing for BIPV roof panels shall be installed in accordance with the roof covering manufacturer’s installation instructions to prevent water from entering the wall and roof through joints in copings, through moisture-permeable materials and at intersections with parapet walls and other penetrations through the roof plane.
SECTION 1508—ROOF INSULATION
[BF] 1508.1 General. The use of above-deck thermal insulation shall be permitted provided that such insulation is covered with an approved roof covering and passes the tests of NFPA 276 or UL 1256 when tested as an assembly.
Exceptions:
- Foam plastic roof insulation shall conform to the material and installation requirements of Chapter 26.
- Where a concrete or composite metal and concrete roof deck is used and the above-deck thermal insulation is covered with an approved roof covering.
CBC § 1511.10.1 High relevance — show source text
1511.10.1 Design. [BSC, DSA-SS, DSA-SS/CC, HCD 1 & HCD 2, OSHPD 1, 1R, 2, 4 & 5] Supports and attachments of photovoltaic panels to the roof structure, the panels, modules and components shall be designed in accordance with this code. 1. Seismic design shall be in accordance with ASCE 7 Section 13.6.12. 2. Wind design pressures shall be determined from ASCE 7 Section 29.4.3 or 29.4.4 using effective wind area in accordance with ASCE 7 Section 26.2.
Construction documents for the supports and attachments shall be submitted to the enforcement agency for approval.
SECTION 1512—REROOFING
1512.1 General. Materials and methods of application used for recovering or replacing an existing roof covering shall comply with the requirements of Chapter 15.
Exceptions:
- Roof replacement or roof recover of existing low-slope roof coverings shall not be required to meet the minimum design slope requirement of [1] / 4 unit vertical in 12 units horizontal (2-percent slope) in Section 1507 for roofs that provide positive roof drainage and meet the requirements of Sections 1608.3 and 1611.2.
- Recovering or replacing an existing roof covering shall not be required to meet the requirement for secondary (emergency overflow) drains or scuppers in Section 1502.2 for roofs that provide for positive roof drainage and meet the requirements of Sections 1608.3 and 1611.2. For the purposes of this exception, existing secondary drainage or scupper systems required in accordance with this code shall not be removed unless they are replaced by secondary drains or scuppers designed and installed in accordance with Section 1502.2.
1512.2 Roof replacement. Roof replacement shall include the removal of all existing layers of roof assembly materials down to the roof deck.
Exceptions:
- Where the existing roof assembly includes an ice barrier membrane that is adhered to the roof deck and the existing sheathing is not water-soaked or deteriorated to the point that it is not adequate as a base for additional roofing, the existing ice barrier membrane shall be permitted to remain in place and covered with an additional layer of ice barrier membrane in accordance with Section 1507 where permitted by the roof covering manufacturer and new ice barrier underlayment manufacturer.
- Where the existing roof includes a self-adhered underlayment and the existing sheathing is not water-soaked or deteriorated to the point that it is not adequate as a base for additional roofing, the existing self-adhered underlayment shall be permitted to remain in place and covered with an underlayment complying with Tables 1507.1.1(1), 1507.1.1(2) and 1507.1.1(3).
- Where the existing roof includes one layer of self-adhered underlayment and the existing layer cannot be removed without damaging the roof deck, a second layer of self-adhered underlayment is permitted to be installed over the existing self-adhered underlayment provided that the following conditions are met: 3.1. It is permitted by the roof covering manufacturer and self-adhered underlayment manufacturer. 3.2. The existing sheathing is not water-soaked or deteriorated to the point that it is not adequate as a base for additional roofing.
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CBC § 0.010 High relevance — show source text
Metal caps shall have a
thickness of not less than 32-gage sheet metal. Power-
driven metal caps shall have a minimum thickness of
0.010 inch. Minimum thickness of the outside edge of
plastic caps shall be 0.035 inch. The cap nail shank shall
be not less than 0.083 inch. The cap nail shank shall have a
length sufficient to penetrate through the roof sheathing
or not less than3/4 inch into the roof sheathing.
Self-adhering polymer modified bitumen underlayment
shall be installed in accordance with the underlayment
and roof covering manufacturers’ installation instruc-
tions for the deck material, roof ventilation configuration
and climate exposure of the roof covering.| |Metal roof shingles|1507.5|1507.5|1507.5| |Mineral-surfaced roll
roofing|1507.6|1507.6|1507.6| |Slate shingles|1507.7|1507.7|1507.7| |Wood shingles|1507.8|1507.8|1507.8| |Wood shakes|1507.9|1507.9|1507.9| |For SI: 1 inch = 25.4 mm, 1 mile per hour = 0.447 m/s.|For SI: 1 inch = 25.4 mm, 1 mile per hour = 0.447 m/s.|For SI: 1 inch = 25.4 mm, 1 mile per hour = 0.447 m/s.|For SI: 1 inch = 25.4 mm, 1 mile per hour = 0.447 m/s.|1507.1.2 Ice barriers. In areas where there has been a history of ice forming along the eaves causing a backup of water, an ice barrier shall be installed for asphalt shingles, metal roof shingles, mineral-surfaced roll roofing, slate and slate-type shingles, wood shingles, and wood shakes. The ice barrier shall consist of not less than two layers of underlayment cemented together, or a self-adhering polymer modified bitumen sheet shall be used in place of normal underlayment and extend from the lowest edges of all roof surfaces to a point not less than 24 inches (610 mm) inside the exterior wall line of the building.
Exception: Detached accessory structures that do not contain conditioned floor area.
1507.2 Asphalt shingles. The installation of asphalt shingles shall comply with the provisions of this section.
1507.2.1 Deck requirements. Asphalt shingles shall be fastened to solidly sheathed decks.
1507.2.2 Slope. Asphalt shingles shall only be used on roof slopes of 2 units vertical in 12 units horizontal (17-percent slope) or greater. For roof slopes from 2 units vertical in 12 units horizontal (17-percent slope) up to 4 units vertical in 12 units horizontal (33-percent slope), double underlayment application is required in accordance with Section 1507.1.1.
1507.2.3 Underlayment. Underlayment shall comply with Section 1507.1.1.
1507.2.4 Asphalt shingles. Asphalt shingles shall comply with ASTM D3462.
CBC § 25.4 High relevance — show source text
447 m/s.|For SI: 1 inch = 25.4 mm, 1 mile per hour = 0.447 m/s.|
1507.1.2 Ice barriers. In areas where there has been a history of ice forming along the eaves causing a backup of water, an ice barrier shall be installed for asphalt shingles, metal roof shingles, mineral-surfaced roll roofing, slate and slate-type shingles, wood shingles, and wood shakes. The ice barrier shall consist of not less than two layers of underlayment cemented together, or a self-adhering polymer modified bitumen sheet shall be used in place of normal underlayment and extend from the lowest edges of all roof surfaces to a point not less than 24 inches (610 mm) inside the exterior wall line of the building.
Exception: Detached accessory structures that do not contain conditioned floor area.
1507.2 Asphalt shingles. The installation of asphalt shingles shall comply with the provisions of this section.
1507.2.1 Deck requirements. Asphalt shingles shall be fastened to solidly sheathed decks.
1507.2.2 Slope. Asphalt shingles shall only be used on roof slopes of 2 units vertical in 12 units horizontal (17-percent slope) or greater. For roof slopes from 2 units vertical in 12 units horizontal (17-percent slope) up to 4 units vertical in 12 units horizontal (33-percent slope), double underlayment application is required in accordance with Section 1507.1.1.
1507.2.3 Underlayment. Underlayment shall comply with Section 1507.1.1.
1507.2.4 Asphalt shingles. Asphalt shingles shall comply with ASTM D3462.
1507.2.5 Fasteners. Fasteners for asphalt shingles shall be galvanized, stainless steel, aluminum or copper roofing nails, minimum 12-gage [0.105 inch (2.67 mm)] shank with a minimum [3] / 8 -inch-diameter (9.5 mm) head, of a length to penetrate through the roofing materials and not less than [3] / 4 inch (19.1 mm) into the roof sheathing. Where the roof sheathing is less than [3] / 4 inch (19.1 mm) thick, the nails shall penetrate through the sheathing. Fasteners shall comply with ASTM F1667.
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1507.2.6 Attachment. Asphalt shingles shall have the minimum number of fasteners required by the manufacturer, but not less than four fasteners per strip shingle or two fasteners per individual shingle. Where the roof slope exceeds 21 units vertical in 12 units horizontal (21:12), shingles shall be installed as required by the manufacturer.
1507.2.7 Ice barrier. Where required, ice barriers shall comply with Section 1507.1.2.
1507.2.8 Flashings. Flashing for asphalt shingles shall comply with this section. Flashing shall be applied in accordance with this section and the asphalt shingle manufacturer’s instructions.
CBC § 2.9 High relevance — show source text
Fire district D102.2.9 Height modifications 503.1.4, 504.3 Impact resistance 1504.7 Insulation 1508 Lightning protection systems 1511.7.6 Materials 1506 Mechanical equipment screen 1511.6 Parapet walls 1503.2, 1503.3 Penthouses 713.12.1, 1511.2 Photovoltaic panels and modules 1511.10, 1511.10.1 Radiant barrier 1510
Tanks 1511.3 Towers, spires, domes and cupolas 1511.5, 3108 Weather protection 1503 Wind resistance 1504.1, 1504.3, 1504.4, 1609.6 Roof Construction Construction walkways 3306.7 Coverings (see Roof Coverings) 1609.6.2 Draftstopping 718.4 Fire resistance Table 601 Fireblocking 718.2 Live loads 1607.14, Table 1607.1,
3111.1.2
Materials Chapter 6 Penetration of fire-resistant assemblies
714 Protection from adjacent construction 3307.1
Rain loads 1611
Roof deck 1609.6.1 Signs, roof mounted H110 Slope, minimum Chapter 15
Snow load 1608 Solar systems, rooftop-mounted 3111.1, 3111.3.2 Trusses 2206.1.3, 2303.4, 2308.11.12 Ventilation 1202.2
Wood (see Roof Construction, Wood) Roof Construction, Wood 602.4, 602.5 Anchorage to walls 1604.8.2 Attic access 1209.2 Ceiling joists 2308.11.1 Diaphragms 2305.1, 2306.2 Fastening requirements 2304.10 Fire-retardant-treated Table 601,
603.1
Framing 2304.11.4, 2308.11 Rafters 2306.1.1, 2308.11.2 Sheathing 2304.8.2, 2308.11.9 Trusses 2303.4, 2308.11.12 Ventilation, attic 1202.2 Wind uplift 2308.11.4 Roof Coverings 1507 Asphalt shingles 1507.2, 1609.2.1 Built up 1507.10 Clay tile 1507.3, 1513 Concrete tile 1507.3, 1513 Fire district D102.2.4
CBC § 1507.6 High relevance — show source text
The metal valley flashing underlayment shall be solidly cemented to the roofing underlayment for roof slopes under seven units vertical in 12 units horizontal (58-percent slope) or selfadhering polymer-modified bitumen sheet shall be installed.
1507.6 Mineral-surfaced roll roofing. The installation of mineral-surfaced roll roofing shall comply with this section.
1507.6.1 Deck requirements. Mineral-surfaced roll roofing shall be fastened to solidly sheathed roofs.
1507.6.2 Deck slope. Mineral-surfaced roll roofing shall not be applied on roof slopes below 1 unit vertical in 12 units horizontal (8-percent slope).
1507.6.3 Underlayment. Underlayment shall comply with Section 1507.1.1.
1507.6.4 Ice barrier. Where required, ice barriers shall comply with Section 1507.1.2.
1507.6.5 Material standards. Mineral-surfaced roll roofing shall conform to ASTM D3909 or ASTM D6380.
1507.7 Slate shingles. The installation of slate shingles shall comply with the provisions of this section.
1507.7.1 Deck requirements. Slate shingles shall be fastened to solidly sheathed roofs.
1507.7.2 Deck slope. Slate shingles shall only be used on slopes of 4 units vertical in 12 units horizontal (4:12) or greater.
1507.7.3 Underlayment. Underlayment shall comply with Section 1507.1.1.
1507.7.4 Ice barrier. Where required, ice barriers shall comply with Section 1507.1.2.
1507.7.5 Material standards. Slate shingles shall comply with ASTM C406.
1507.7.6 Application. Minimum headlap for slate shingles shall be in accordance with Table 1507.7.6. Slate shingles shall be secured to the roof with two fasteners per slate.
TABLE 1507.7.6—SLATE SHINGLE HEADLAP Col2 SLOPE HEADLAP (inches) 4:12 < slope < 8:12 4 8:12 < slope < 20:12 3 slope ≥ 20:12 2 For SI: 1 inch = 25.4 mm. For SI: 1 inch = 25.4 mm. 1507.7.7 Flashing. Flashing and counterflashing shall be made with sheet metal. Valley flashing shall be not less than 15 inches (381 mm) wide. Valley and flashing metal shall be a minimum uncoated thickness of 0.0179-inch (0.455 mm) zinc-coated G90. Chimneys, stucco or brick walls shall have not fewer than two plies of felt for a cap flashing consisting of a 4-inch-wide (102 mm)
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strip of felt set in plastic cement and extending 1 inch (25 mm) above the first felt and a top coating of plastic cement. The felt shall extend over the base flashing 2 inches (51 mm).
CBC § 14-3 High relevance — show source text
1402 Performance Requirements . . . . . . . . . . . . . . . . . . . . 14-3
1403 Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-4
1404 Installation of Wall Coverings. . . . . . . . . . . . . . . . . . . 14-5
1405 Combustible Materials on the Exterior Side of
Exterior Walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-16
1406 Metal Composite Material (MCM). . . . . . . . . . . . . . . 14-17
1407 Exterior Insulation and Finish Systems (EIFS). . . . 14-18
1408 High-Pressure Decorative Exterior-Grade Compact Laminates (HPL). . . . . . . . . . . . . . . . . . . 14-18
1409 Insulated Metal Panel (IMP) . . . . . . . . . . . . . . . . . . . 14-19
1410 Plastic Composite Decking . . . . . . . . . . . . . . . . . . . . 14-21 1411 Building-Integrated Photovoltaic (BIPV) Systems for Exterior Wall Coverings and Fenestration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-21
1412 Soffits and Fascias at Roof Overhangs . . . . . . . . . . 14-21
1413 [DSA-SS & DSA-SS/CC, OSHPD 1, 1R, 2, 4 & 5] Additional Requirements for Anchored and Adhered Veneer. . . . . . . . . . . . . . 14-23
CHAPTER 15 ROOF ASSEMBLIES AND ROOFTOP
STRUCTURES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-1
1501 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-3
1502 Roof Drainage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-3
1503 Weather Protection. . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-3
1504 Performance Requirements . . . . . . . . . . . . . . . . . . . . 15-3
1505 Fire Classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-5
1506 Materials. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-6
1507 Requirements for Roof Coverings . . . . . . . . . . . . . . . 15-7
CBC § 1507.1.1 High relevance — show source text
An approved
underlayment complying with Table 1507.1.1(1) for
the applicable roof covering and basic wind speed
shall be applied over the entire roof over the 4-inch-
wide membrane strips. Underlayment shall be
applied in accordance with this table using the
application requirements for where the maximum
basic wind speed is less than 130 mph.
3.
A single layer of self-adhering polymer modified
bitumen underlayment complying with ASTM
D1970, installed in accordance with the
underlayment and roof covering manufacurers’
installation instructions for the deck material, roof
ventilation configuration and climate exposure of
the roof covering.| |Clay and
concrete
tile|1507.3|Underlayment shall be one of the following:
1.
For roof slopes from 21/2 units vertical in 12 units
horizontal (21/2:12) to 4 units vertical in 12 units
horizontal (4:12), underlayment shall be not fewer
than two layers applied in the following manner:
Apply a strip of underlayment that is half the width
of a full sheet parallel to and starting at the eaves.
Starting at the eaves, a full-width strip of
underlayment felt shall be applied, overlapping
successive sheets half the width of a full sheet plus 2
inches. End laps shall be 4 inches and shall be offset
by 6 feet.
2.
For roof slopes of 4 units vertical in 12 units
horizontal (4:12) or greater, underlayment shall be
one layer applied as follows: Underlayment shall be
applied shingle fashion, parallel to and starting from
the eaves and lapped 2 inches. End laps shall be 4
inches and shall be offset by 6 feet.
3.
A single layer of self-adhering polymer modified
bitumen underlayment complying with ASTM
D1970, installed in accordance with the
underlayment and roof covering manufacturers’
installation instructions for the deck material, roof
ventilation configuration, and climate exposure of
the roof covering.|Underlayment shall be one of the following:
1.
Two layers of mechanically fastened underlayment
applied in the following manner: Apply a strip of
underlayment that is half the width of a full sheet
parallel to and starting at the eaves, fastened
sufficiently to hold in place. Starting at the eaves,
apply full-width sheets of underlayment,
overlapping successive sheets half the width of a full
sheet plus 2 inches. Distortions in the underlayment
shall not interfere with the ability of the shingles to
seal. End laps shall be 4 inches and shall be offset by
6 feet.
2.
A strip not less than 4 inches in width of self-
adhering polymer modified bitumen underlayment
complying with ASTM D1970, installed in
accordance with the manufacturer’s installation
instructions for the deck material, shall be applied
over all joints in the roof decking. An approved
underlayment complying with Table 1507.1.1(1) for
the applicable roof covering and basic wind speed
shall be applied over the entire roof over the 4-inch-
wide membrane strips.CBC § 4.1 High relevance — show source text
For roof slopes of 3 units vertical in 12 units horizontal (25-percent slope) and greater, valley flashing shall have a 36-inch-wide (914 mm) underlayment of one layer of Type I underlayment running the full length of the valley, in addition to other required underlayment. In areas where the average daily temperature in January is 25°F (-4°C) or less, metal valley flashing underlayment shall be solid-cemented to the roofing underlayment for slopes less than 7 units vertical in 12 units horizontal (58-percent slope) or be of self-adhering polymer-modified bitumen sheet.
R905.4 Metal roof shingles. The installation of metal roof shingles shall comply with the provisions of this section.
R905.4.1 Sheathing requirements. Metal roof shingles shall be fastened to wood structural panels, solid lumber sheathing or closely fitted lumber sheathing, except where the roof covering is specifically designed to be applied to spaced lumber sheathing.
R905.4.2 Slope. Metal roof shingles shall not be installed on roof slopes below 3 units vertical in 12 units horizontal (25-percent slope).
R905.4.3 Underlayment. Underlayment shall comply with Section R905.1.1.
R905.4.3.1 Ice barrier. Where required, ice barriers shall comply with Section R905.1.2.
R905.4.4 Material standards. Metal roof shingle roof coverings shall comply with Table R905.10.3(1). The materials used for metal roof shingle roof coverings shall be naturally corrosion resistant or be made corrosion resistant in accordance with the standards and minimum thicknesses listed in Table R905.10.3(2).
R905.4.4.1 Wind resistance of metal roof shingles. Metal roof shingles fastened to wood structural panels, solid lumber sheathing or closely fitted lumber sheathing shall be tested in accordance with ASTM D3161, FM 4474, UL 580 or UL 1897. Metal roof shingles tested in accordance with ASTM D3161 shall meet the classification requirements of Table R905.4.4.1 for the appropriate maximum basic wind speed and the metal shingle packaging shall bear a label to indicate compliance with ASTM D3161 and the required classification in Table R905.2.4.1.
9-10 2025 CALIFORNIA RESIDENTIAL CODE
on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.
ROOF ASSEMBLIES
CBC § 14-23 High relevance — show source text
1413 [DSA-SS & DSA-SS/CC, OSHPD 1, 1R, 2, 4 & 5] Additional Requirements for Anchored and Adhered Veneer. . . . . . . . . . . . . . 14-23
CHAPTER 15 ROOF ASSEMBLIES AND ROOFTOP
STRUCTURES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-1
1501 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-3
1502 Roof Drainage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-3
1503 Weather Protection. . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-3
1504 Performance Requirements . . . . . . . . . . . . . . . . . . . . 15-3
1505 Fire Classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-5
1506 Materials. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-6
1507 Requirements for Roof Coverings . . . . . . . . . . . . . . . 15-7
1508 Roof Insulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15-20
1509 Roof Coatings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15-20
1510 Radiant Barriers Installed Above Deck . . . . . . . . . .15-21
1511 Rooftop Structures . . . . . . . . . . . . . . . . . . . . . . . . . . .15-21
1512 Reroofing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15-24
1513 [DSA-SS & DSA-SS/CC, OSHPD 1, 1R, 2, 4 & 5] Seismic Anchorage of Slate Shingle, Clay and Concrete Tile Roof Coverings. . . . . . . 15-25
INDEX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . INDEX-1
HISTORY NOTE TO VOLUME 1 . . . . . . . . . . . . . . . . . . . . . .HIST-1
VOLUME 2
CHAPTER 16 STRUCTURAL DESIGN . . . . . . . . . . . . . . . . . .16-1
Frequently asked questions
Do I always need an ice barrier in California?
No. An ice barrier is required only in areas "where there has been a history of ice forming along the eaves causing a backup of water" per § 1507.1.2; if that local climate trigger is met, the barrier must extend at least 24 inches inside the exterior wall line .
Can I use a single layer of self‑adhering membrane (ASTM D1970) everywhere?
The CBC allows a single layer of self‑adhering polymer‑modified bitumen underlayment complying with ASTM D1970 as an option in many table entries, but manufacturer instructions, deck type, slope, ventilation and specific roof‑covering provisions must be followed; certain coverings and residential code sections may place additional limits — always confirm the specific roof covering section and manufacturer's instructions (§ 1507.1.1 and Table 1507.1.1(1)) .
How far inland do I have to extend an ice barrier?
Where required, the ice barrier must extend from the lowest edges of all roof surfaces to a point not less than 24 inches (610 mm) inside the exterior wall line of the building per § 1507.1.2 .
Is double underlayment always determined by slope?
Not always — slope is a common trigger (for example, asphalt shingles between 2:12 and 4:12 require double underlayment under § 1507.2.2), but Table 1507.1.1(1) and the roof‑covering sections may also require double layers based on covering type, decking joints, or other local exposure/wind conditions .
If I'm reroofing over an existing self‑adhered underlayment, can I leave it in place?
The CBC (§ 1512.2) permits leaving an existing adhered ice barrier or self‑adhered underlayment in place in limited circumstances if the existing sheathing is not water‑soaked or deteriorated and the new materials are compatible and the manufacturer permits it; see the reroofing exceptions in § 1512.2 for the full conditions .
More in California Building Code
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