ADOPTS WITH AMENDMENTS:

International Residential Code 2018 (IRC 2018)

Part I — Administrative

Part II — Definitions

Part III — Building Planning and Construction

Part IV — Energy Conservation

Part V — Mechanical

Part VI — Fuel Gas

Part VII — Plumbing

Part VIII — Electrical

Part IX — Referenced Standards

Heads up: There are no amended sections in this chapter.

The provisions of this chapter shall control the design and construction of the roof-ceiling system for buildings.

Exception: Buildings and structures located within the High-Velocity Hurricane Zone shall comply with the provisions of Chapter 44.

Roof and ceiling construction shall be capable of accommodating all loads imposed in accordance with Section R301 and of transmitting the resulting loads to the supporting structural elements.
In areas where expansive or collapsible soils are known to exist, all dwellings shall have a controlled method of water disposal from roofs that will collect and discharge roof drainage to the ground surface not less than 5 feet (1524 mm) from foundation walls or to an approved drainage system.
Wood and wood-based products used for load-supporting purposes shall conform to the applicable provisions of this section.
Sawn lumber shall be identified by a grade mark of an accredited lumber grading or inspection agency and have design values certified by an accreditation body that complies with DOC PS 20. In lieu of a grade mark, a certificate of inspection issued by a lumber grading or inspection agency meeting the requirements of this section shall be accepted.
Approved end-jointed lumber identified by a grade mark conforming to Section R802.1.1 shall be permitted to be used interchangeably with solid-sawn members of the same species and grade. End-jointed lumber used in an assembly required elsewhere in this code to have a fire-resistance rating shall have the designation "Heat-Resistant Adhesive" or "HRA" included in its grade mark.
Glued laminated timbers shall be manufactured and identified as required in ANSI A190.1, ANSI 117 and ASTM D3737.
Structural log members shall comply with the provisions of ICC 400.
Structural capacities for structural composite lumber shall be established and monitored in accordance with ASTM D5456.
Fire-retardant-treated wood (FRTW) is any wood product that, when impregnated with chemicals by a pressure process or other means during manufacture, shall have, when tested in accordance with ASTM E84 or UL 723, a listed flame spread index of 25 or less and shows no evidence of significant progressive combustion where the test is continued for an additional 20-minute period. In addition, the flame front shall not progress more than 10.5 feet (3200 mm) beyond the center line of the burners at any time during the test.
For wood products impregnated with chemicals by a pressure process, the process shall be performed in closed vessels under pressures not less than 50 pounds per square inch gauge (psig) (344.7 kPa).
For wood products produced by other means during manufacture the treatment shall be an integral part of the manufacturing process of the wood product. The treatment shall provide permanent protection to all surfaces of the wood product.
For wood products produced by other means during manufacture, other than a pressure process, all sides of the wood product shall be tested in accordance with and produce the results required in Section R802.1.5. Testing of only the front and back faces of wood structural panels shall be permitted.

Fire-retardant-treated lumber and wood structural panels shall be labeled. The label shall contain:

  1. The identification mark of an approved agency in accordance with Section 1703.5 of the Florida Building Code, Building.
  2. Identification of the treating manufacturer.
  3. The name of the fire-retardant treatment.
  4. The species of wood treated.
  5. Flame spread index and smoke-developed index.
  6. Method of drying after treatment.
  7. Conformance to applicable standards in accordance with Sections R802.1.5.5 through R802.1.5.10.
  8. For FRTW exposed to weather, or a damp or wet location, the words "No increase in the listed classification when subjected to the Standard Rain Test" (ASTM D2898).
Design values for untreated lumber and wood structural panels as specified in Section R802.1 shall be adjusted for fire-retardant-treated wood. Adjustments to design values shall be based upon an approved method of investigation that takes into consideration the effects of the anticipated temperature and humidity to which the fire-retardant-treated wood will be subjected, the type of treatment and redrying procedures.
The effect of treatment and the method of redrying after treatment, and exposure to high temperatures and high humidities on the flexure properties of fire-retardant-treated soft-wood plywood shall be determined in accordance with ASTM D5516. The test data developed by ASTM D5516 shall be used to develop adjustment factors, maximum loads and spans, or both for untreated plywood design values in accordance with ASTM D6305. Each manufacturer shall publish the allowable maximum loads and spans for service as floor and roof sheathing for their treatment.
For each species of wood treated, the effect of the treatment and the method of redrying after treatment and exposure to high temperatures and high humidities on the allowable design properties of fire-retardant-treated lumber shall be determined in accordance with ASTM D5664. The test data developed by ASTM D5664 shall be used to develop modification factors for use at or near room temperature and at elevated temperatures and humidity in accordance with ASTM D6841. Each manufacturer shall publish the modification factors for service at temperatures of not less than 80°F (27°C) and for roof framing. The roof framing modification factors shall take into consideration the climatological location.
Where fire-retardant-treated wood is exposed to weather or damp or wet locations, it shall be identified as "Exterior" to indicate there is not an increase in the listed flame spread index as defined in Section R802.1.5 when subjected to ASTM D2898.
Interior fire-retardant-treated wood shall have a moisture content of not over 28 percent when tested in accordance with ASTM D3201 procedures at 92-percent relative humidity. Interior fire-retardant-treated wood shall be tested in accordance with Section R802.1.5.6 or R802.1.5.7. Interior fire-retardant-treated wood designated as Type A shall be tested in accordance with the provisions of this section.
Fire-retardant-treated wood shall be dried to a moisture content of 19 percent or less for lumber and 15 percent or less for wood structural panels before use. For wood kiln dried after treatment (KDAT) the kiln temperatures shall not exceed those used in kiln drying the lumber and plywood submitted for the tests described in Section R802.1.5.6 for plywood and R802.1.5.7 for lumber.
Cross-laminated timber shall be manufactured and identified as required by ANSI/APA PRG 320.
Engineered wood rim boards shall conform to ANSI/APA PRR 410 or shall be evaluated in accordance with ASTM D7672. Structural capacities shall be in accordance with ANSI/APA PRR 410 or established in accordance with ASTM D7672. Rim boards conforming to ANSI/APA PRR 410 shall be marked in accordance with that standard.
Structural capacities and design provisions for prefabricated wood I-joists shall be established and monitored in accordance with ASTM D5055.
Wood roof framing shall be in accordance with Section R301.2.1.1 or ANSI AWC NDS.

R802.3 Framing Details

ILLUSTRATION
Reserved.
Reserved.

Reserved.

Table R802.4(1)

Ceiling Joist Spans for Common Lumber Species.

Reserved.

Table R802.4(2)

Ceiling Joist Spans for Common Lumber Species.

Reserved.

Reserved.

Table R802.5.1(1)

Rafter Spans for Common Lumber Species.

Reserved.

Table R802.5.1(2)

Rafter Spans for Common Lumber Species.

Reserved.

Table R802.5.1(3)

Rafter Spans for Common Lumber Species.

Reserved.

Table R802.5.1(4)

Rafter Spans for Common Lumber Species.

Reserved.

Table R802.5.1(5)

Rafter Spans for Common Lumber Species.

Reserved.

Table R802.5.1(6)

Rafter Spans for Common Lumber Species.

Reserved.

Table R802.5.1(7)

Rafter Spans for 70 PSF Ground Snow Load.

Reserved.

Table R802.5.1(8)

Rafter Spans for 70 PSF Ground Snow Load.

Reserved.

Table R802.5.1(9)

Rafter/Ceiling Joist Heel Joint Connections.

Reserved.

Figure 802.5.1

Braced Rafter Construction.

Reserved.

Reserved.
Structural roof members shall not be cut, bored or notched in excess of the limitations specified in this section.
Cuts, notches and holes in solid lumber joists, rafters, blocking and beams shall comply with the provisions of Section R502.2 except that cantilevered portions of rafters shall be permitted in accordance with Section R802.7.1.1.

Notches on cantilevered portions of rafters are permitted provided the dimension of the remaining portion of the rafter is not less than 31/2 inches (89 mm) and the length of the cantilever does not exceed 24 inches (610 mm) in accordance with Figure R802.7.1.1.

For SI: 1 inch = 25.4 mm.

FIGURE R802.7.1.1

RAFTER NOTCH

Taper cuts at the ends of the ceiling joist shall not exceed one-fourth the depth of the member in accordance with Figure R802.7.1.2.

FIGURE R802.7.1.2

CEILING JOIST TAPER CUT

Cuts, notches and holes bored in trusses, structural composite lumber, structural glue-laminated members, cross-laminated timber members or I-joists are prohibited except where permitted by the manufacturer's recommendations or where the effects of such alterations are specifically considered in the design of the member by a registered design professional.
Reserved.

Truss design drawings, prepared in conformance to Section R802.10.1, shall be provided to the building official and approved prior to installation. Truss design drawings shall be provided with the shipment of trusses delivered to the job site. Truss design drawings shall include, at a minimum, the following information:

  1. Slope or depth, span and spacing.
  2. Location of all joints.
  3. Required bearing widths.
  4. Design loads as applicable.

    1. 4.1. Top chord live load (as determined from Section R301.6).
    2. 4.2. Top chord dead load.
    3. 4.3. Bottom chord live load.
    4. 4.4. Bottom chord dead load.
    5. 4.5. Concentrated loads and their points of application.
    6. 4.6. Controlling wind and earthquake loads.
  5. Adjustments to lumber and joint connector design values for conditions of use.
  6. Each reaction force and direction.
  7. Joint connector type and description such as size, thickness or gage and the dimensioned location of each joint connector except where symmetrically located relative to the joint interface.
  8. Lumber size, species and grade for each member.
  9. Connection requirements for:

    1. 9.1. Truss to girder-truss.
    2. 9.2. Truss ply to ply.
    3. 9.3. Field splices.
  10. Calculated deflection ratio and/or maximum description for live and total load.
  11. Maximum axial compression forces in the truss members to enable the building designer to design the size, connections and anchorage of the permanent continuous lateral bracing. Forces shall be shown on the truss design drawing or on supplemental documents.
  12. Required permanent truss member bracing location.
Wood trusses shall be designed in accordance with accepted engineering practice. The design and manufacture of metal-plate-connected wood trusses shall comply with ANSI/TPI 1. The truss design drawings shall be prepared by a registered professional where required by the Florida Statutes.
The provisions of this section shall control the design of truss roof framing when snow controls for buildings, not greater than 60 feet (18 288 mm) in length perpendicular to the joist, rafter or truss span, not greater than 36 feet (10 973 mm) in width parallel to the joist, rafter or truss span, not more than three stories above grade plane in height, and roof slopes not smaller than 3:12 (25 percent slope) or greater than 12:12 (100-percent slope). Truss roof framing constructed in accordance with the provisions of this section shall be limited to sites subjected to a maximum design wind speed of 140 miles per hour (63 m/s), Exposure B or C, and a maximum ground snow load of 70 psf (3352 Pa). For consistent loading of all truss types, roof snow load is to be computed as: 0.7 pg.
Trusses shall be braced to prevent rotation and provide lateral stability in accordance with the requirements specified in the construction documents for the building and on the individual truss design drawings. In the absence of specific bracing requirements, trusses shall be braced in accordance with accepted industry practice such as the SBCA Building Component Safety Information (BCSI) Guide to Good Practice for Handling, Installing & Bracing of Metal Plate Connected Wood Trusses.
Truss members shall not be cut, notched, drilled, spliced or otherwise altered in any way without the approval of a registered design professional. Alterations resulting in the addition of load such as HVAC equipment water heater that exceeds the design load for the truss shall not be permitted without verification that the truss is capable of supporting such additional loading.

Reserved.

Table R802.11

Rafter or Truss Uplift Connection Forces from Wind (ASD) (Pounds Per Connection).

Reserved.

Allowable spans for lumber used as roof sheathing shall conform to Table R803.1. Spaced lumber sheathing for wood shingle and shake roofing shall conform to the requirements of Sections R905.7 and R905.8. Spaced lumber sheathing is not allowed in Seismic Design Category D2.

TABLE R803.1

MINIMUM THICKNESS OF LUMBER ROOF SHEATHING

RAFTER OR BEAM SPACING
(inches)
MINIMUM NET THICKNESS
(inches)
24 5/8
48a 11/2 T & G
60b
72c

For SI: 1 inch = 25.4 mm.

  1. Minimum 270 Fb, 340,000 E.
  2. Minimum 420 Fb, 660,000 E.
  3. Minimum 600Fb, 1,150,000 E.
Wood structural panels shall conform to DOC PS 1, DOC PS 2, CSA O437 or CSA O325, and shall be identified for grade, bond classification and performance category by a grade mark or certificate of inspection issued by an approved agency. Wood structural panels shall comply with the grades specified in Section R503.1.
Wood structural panels, when designed to be permanently exposed in outdoor applications, shall be of an exterior exposure durability. Wood structural panel roof sheathing exposed to the underside shall be permitted to be of interior type bonded with exterior glue, identified as Exposure 1.
The allowable unit stresses for fire-retardant-treated plywood, including fastener values, shall be developed from an approved method of investigation that considers the effects of anticipated temperature and humidity to which the fire-retardant-treated plywood will be subjected, the type of treatment and redrying process. The fire-retardant-treated plywood shall be graded by an approved agency.

The minimum thickness and span rating for wood structural panel roof sheathing shall not exceed the values set forth in Table R803.2.2.

TABLE R803.2.2

MINIMUM ROOF SHEATHING THICKNESS

Rafter/Truss Spacing
24 in. o.c.
WIND SPEED
115 mph 120 mph 130 mph 140 mph 150 mph 160 mph 170 mph 180 mph
Minimum Sheathing Thickness, inches
(Panel Span Rating) Exposure B
7/16
(24/16)
7/16
(24/16)
7/16
(24/16)
7/16
(24/16)
15/32
(32/16)
19/32
(40/20)
19/32
(40/20)
19/32
(40/20)
Minimum Sheathing Thickness, inches
(Panel Span Rating) Exposure C
7/16
(24/16)
7/16
(24/16)
15/32
(32/16)
19/32
(40/20)
19/32
(40/20)
19/32
(40/20)
19/32
(40/20)
23/32
(48/24)
Minimum Sheathing Thickness, inches
(Panel Span Rating) Exposure D
15/32
(32/16)
19/32
(40/20)
19/32
(40/20)
19/32
(40/20)
19/32
(40/20)
19/32
(40/20)
23/32
(48/24)
23/32
(48/24)
Wood structural panel used as roof sheathing shall be installed with joints staggered in accordance with Section R803.2.3.1 for wood roof framing or with Section R804.1 for cold-formed steel roof framing. Wood structural panel roof sheathing shall not cantilever more than 9 inches beyond the gable end wall unless supported by gable overhang framing.

Wood structural panel sheathing shall be fastened to roof framing in accordance with Table R803.2.3.1. Where the sheathing thickness is 15/32 inches and less, sheathing shall be fastened with ASTM F1667 RSRS-01 (23/8" × 0.113") nails. Where the sheathing thickness is greater than 15/32 inches, sheathing shall be fastened with ASTM F1667 RSRS-03 (21/2" × 0.131") nails or ASTM F1667 RSRS-04 (3" × 0.120") nails. RSRS-01, RSRS-03 and RSRS-04 are ring shank nails meeting the specifications in ASTM F1667.

TABLE R803.2.3.1

ROOF SHEATHING ATTACHMENTa, b

Rafter/Truss Spacing
24 in. o.c.
WIND SPEED
115 mph 120 mph 130 mph 140 mph 150 mph 160 mph 170 mph 180 mph
E F E F E F E F E F E F E F E F
Exposure B
Rafter/Truss SG = 0.42 6 6 6 6 6 6 6 6 6 6 4 4 4 4 4 4
Rafter/Truss SG = 0.49 6 12 6 12 6 6 6 6 6 6 6 6 6 6 6 6
Exposure C
Rafter/Truss SG = 0.42 6 6 6 6 6 6 4 4 4 4 4 4 3 3 3 3
Rafter/Truss SG = 0.49 6 6 6 6 6 6 6 6 6 6 6 6 4 4 4 4
Exposure D
Rafter/Truss SG = 0.42 6 6 6 6 4 4 4 4 4 4 3 3 3 3 3 3
Rafter/Truss SG = 0.49 6 6 6 6 6 6 6 6 4 4 4 4 4 4 4 4

E = Nail spacing along panel edges (inches)

F = Nail spacing along intermediate supports in the panel field (inches)

  1. For sheathing located a minimum of 4 feet from the perimeter edge of the roof, including 4 feet on each side of ridges and hips, nail spacing is permitted to be 6 inches on center along panel edges and 6 inches on center along intermediate supports in the panel field.
  2. Where rafter/truss spacing is less than 24 inches on center, roof sheathing fastening is permitted to be in accordance with the AWC WFCM or the AWC NDS.
In accordance with Section R301.2.1.1, the design of cold-formed steel roof framing shall be in accordance with AISI S230, Standard for Cold-Formed Steel Framing—Prescriptive Method For One- and Two-Family Dwellings.
Ceilings shall be installed in accordance with the requirements for interior wall finishes as provided in Section R702.
Enclosed attics and enclosed rafter spaces formed where ceilings are applied directly to the underside of roof rafters shall have cross ventilation for each separate space by ventilating openings protected against the entrance of rain or snow. Ventilation openings shall have a least dimension of 1/16 inch (1.6 mm) minimum and 1/4 inch (6.4 mm) maximum. Ventilation openings having a least dimension larger than 1/4 inch (6.4 mm) shall be provided with corrosion-resistant wire cloth screening, hardware cloth, perforated vinyl or similar material with openings having a least dimension of 1/16 inch (1.6 mm) minimum and 1/4 inch (6.4 mm) maximum. Openings in roof framing members shall conform to the requirements of Section R802.7. Required ventilation openings shall open directly to the outside air and shall be protected to prevent the entry of birds, rodents, snakes and other similar creatures.

The minimum net free ventilating area shall be 1/150 of the area of the vented space.

Exception: The minimum net free ventilation area shall be 1/300 of the vented space, provided that not less than 40 percent and not more than 50 percent of the required ventilating area is provided by ventilators located in the upper portion of the attic or rafter space. Upper ventilators shall be located not more than 3 feet (914 mm) below the ridge or highest point of the space, measured vertically. The balance of the required ventilation provided shall be located in the bottom one-third of the attic space. Where the location of wall or roof framing members conflicts with the installation of upper ventilators, installation more than 3 feet (914 mm) below the ridge or highest point of the space shall be permitted.

Where eave or cornice vents are installed, blocking, bridging and insulation shall not block the free flow of air. Not less than a 1-inch (25 mm) space shall be provided between the insulation and the roof sheathing and at the location of the vent.
Ventilators shall be installed in accordance with manufacturer's instructions. Installation of ventilators in roof systems shall be in accordance with the requirements of Section R903. Installation of ventilators in wall systems shall be in accordance with the requirements of Section R703.1.

Unvented attics and unvented enclosed roof framing assemblies created by ceilings that are applied directly to the underside of the roof framing members and structural roof sheathing applied directly to the top of the roof framing members/rafters, shall be permitted where all the following conditions are met:

  1. The unvented attic space is completely within the building thermal envelope.
  2. No interior Class I vapor retarders are installed on the ceiling side (attic floor) of the unvented attic assembly or on the ceiling side of the unvented enclosed roof framing assembly.
  3. Where wood shingles or shakes are used, a minimum 1/4-inch (6.4 mm) vented airspace separates the shingles or shakes and the roofing underlayment above the structural sheathing.
  4. In Climate Zones 5, 6, 7 and 8, any air-impermeable insulation shall be a Class II vapor retarder, or shall have a Class II vapor retarder coating or covering in direct contact with the underside of the insulation.
  5. Insulation shall comply with Item 5.3 and Item 5.1. As an alternative, where air-permeable insulation is located on top of the attic floor or on top of the attic ceiling, insulation shall comply with Item 5.3 and Item 5.2.

    1. 5.1. Item 5.1.1, 5.1.2, 5.1.3 or 5.1.4 shall be met, depending on the air permeability of the insulation directly under the structural roof sheathing.

      1. 5.1.1. Where only air-impermeable insulation is provided, it shall be applied in direct contact with the underside of the structural roof sheathing.
      2. 5.1.2. Where air-permeable insulation is provided inside the building thermal envelope, it shall be installed in accordance with Section 5.1.1. In addition to the air-permeable insulation installed directly below the structural sheathing, rigid board or sheet insulation shall be installed directly above the structural roof sheathing in accordance with the R-values in Table R806.5 for condensation control.
      3. 5.1.3. Where both air-impermeable and air-permeable insulation are provided, the air-impermeable insulation shall be applied in direct contact with the underside of the structural roof sheathing in accordance with Item 5.1.1 and shall be in accordance with the R-values in Table R806.5 for condensation control. The air-permeable insulation shall be installed directly under the air-impermeable insulation.
      4. 5.1.4. Alternatively, sufficient rigid board or sheet insulation shall be installed directly above the structural roof sheathing to maintain the monthly average temperature of the underside of the structural roof sheathing above 45°F (7°C). For calculation purposes, an interior air temperature of 68°F (20°C) is assumed and the exterior air temperature is assumed to be the monthly average outside air temperature of the three coldest months.
    2. 5.2. In Climate Zones 1, 2 and 3, air-permeable insulation installed in unvented attics on the top of the attic floor or on top of the ceiling shall meet the following requirements:

      1. 5.2.1. An approved vapor diffusion port shall be installed not more than 12 inches (305 mm) from the highest point of the roof, measured vertically from the highest point of the roof to the lower edge of the port.
      2. 5.2.2. The port area shall be greater than or equal to 1:600 of the ceiling area. Where there are multiple ports in the attic, the sum of the port areas shall be greater than or equal to the area requirement.
      3. 5.2.3. The vapor-permeable membrane in the vapor diffusion port shall have a vapor permeance rating of greater than or equal to 20 perms when tested in accordance with Procedure A of ASTM E96.
      4. 5.2.4. The vapor diffusion port shall serve as an air barrier between the attic and the exterior of the building.
      5. 5.2.5. The vapor diffusion port shall protect the attic against the entrance of rain and snow.
    3. 5.3. Where preformed insulation board is used as the air-impermeable insulation layer, it shall be sealed at the perimeter of each individual sheet interior surface to form a continuous layer.

TABLE R806.5

INSULATION FOR CONDENSATION CONTROL

CLIMATE ZONE MINIMUM RIGID BOARD
ON AIR-IMPERMEABLE
INSULATION R-VALUEa, b
2B and 3B tile roof only 0 (none required)
1, 2A, 2B, 3A, 3B, 3C R-5
4C R-10
4A, 4B R-15
5 R-20
6 R-25
7 R-30
8 R-35
  1. Contributes to but does not supersede the requirements in Section R402 of the Florida Building Code, Energy Conservation.
  2. Alternatively, sufficient continuous insulation shall be installed directly above the structural roof sheathing to maintain the monthly average temperature of the underside of the structural roof sheathing above 45°F (7°C). For calculation purposes, an interior air temperature of 68°F (20°C) is assumed and the exterior air temperature is assumed to be the monthly average outside air temperature of the three coldest months.

Buildings with combustible ceiling or roof construction shall have an attic access opening to attic areas that have a vertical height of 30 inches (762 mm) or greater over an area of not less than 30 square feet (2.8 m2).

The vertical height shall be measured from the top of the ceiling framing members to the underside of the roof framing members.

The rough-framed opening shall be not less than 22 inches by 30 inches (559 mm by 762 mm) and shall be located in a hallway or other location with ready access. Where located in a wall, the opening shall be not less than 22 inches wide by 30 inches high (559 mm wide by 762 mm high). Where the access is located in a ceiling, minimum unobstructed headroom in the attic space shall be 30 inches (762 mm) at some point above the access measured vertically from the bottom of ceiling framing members. See Section M1305.1.3 for access requirements where mechanical equipment is located in attics.

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