Roof-Ceiling Construction

Application.

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.

Requirements.

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.

Roof drainage.

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.

General.

Wood and wood-based products used for load-supporting purposes shall conform to the applicable provisions of this section.

Truss design drawings.

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.

Design.

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.

Bracing.

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.

Alterations to trusses.

Truss members shall not be cut, notched, drilled, spliced or otherwise altered in any way without the approval of a registered design professional.

Sawn lumber.

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.

Roof tie-down.

Reserved. Table R802.11 Rafter or Truss Uplift Connection Forces from Wind (ASD) (Pounds Per Connection).

End-jointed lumber.

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.

Truss uplift resistance.

Reserved.

Rafter uplift resistance.

Reserved. SECTION R803 ROOF SHEATHING

Structural glued laminated timbers.

Glued laminated timbers shall be manufactured and identified as required in ANSI A190.1, ANSI 117 and ASTM D3737.

Structural log members.

Structural log members shall comply with the provisions of ICC 400.

Structural composite lumber.

Structural capacities for structural composite lumber shall be established and monitored in accordance with ASTM D5456.

Fire-retardant-treated wood.

Fire-retardanttreated 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.

Pressure process.

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).

Moisture content.

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.

Other means during manufacture.

For wood products impregnated with chemicals 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.

Testing.

For fire-retardant-treated wood products, the front and back faces of the wood product shall be tested in accordance with and produce the results required in Section R802.1.5.

Fire testing of wood structural panels.

Wood structural panels shall be tested with a ripped or cut longitudinal gap of 1/8 inch (3.2 mm).

Labeling.

Fire-retardant-treated lumber and wood structural panels shall be labeled. The label shall contain: 1.

Strength adjustments.

Design values for untreated lumber and wood structural panels as specified in Section R802.1 shall be adjusted for fire-retardant-treated wood.

Wood structural panels.

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 softwood plywood shall be determined in accordance with ASTM D5516.

Lumber.

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.

Exposure to weather.

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 applications.

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.

Cross-laminated timber.

Cross-laminated timber shall be manufactured and identified as required by ANSI/APA PRG 320.

Engineered wood rim board.

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.

Prefabricated wood I-joists.

Structural capacities and design provisions for prefabricated wood I-joists shall be established and monitored in accordance with ASTM D5055.

Design and construction.

Wood roof framing shall be in accordance with Section R301.2.1.1 or ANSI AWC NDS.

Ceiling joist and rafter connections.

Reserved.

Ceiling joists lapped.

Reserved.

Allowable ceiling joist spans.

Reserved. Table R802.4(1) Ceiling Joist Spans for Common Lumber Species.

Allowable rafter spans.

Reserved.

Purlins.

Reserved. Table R802.5.1(1) Rafter Spans for Common Lumber Species.

Finished ceiling material.

Reserved.

Cutting, drilling and notching.

Structural roof members shall not be cut, bored or notched in excess of the limitations specified in this section.

Sawn lumber.

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.

Cantilevered portions of rafters.

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.

Ceiling joist taper cut.

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

Engineered wood products.

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...

Lumber sheathing.

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.

Wood structural panel sheathing.

Wood structural panel sheathing.

Identification and grade.

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.

Exposure durability.

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.

Fire-retardant-treated plywood.

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 treatme...

Allowable spans.

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.

Installation.

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.

Sheathing fastenings.

Wood structural panel sheathing shall be fastened to roof framing in accordance with Table R803.2.3.1.Sheathing shall be fastened with ASTM F1667 RSRS-03 (21/2" × 0.131" × 0.281 head diameter) nails except that ASTM F1667 RSRS-01 (23/8" × 0.113") nails or ASTM F1667 RSRS-04 (3" × 0.120" × 0.281 head...

General.

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. SECTION R805 CEILING FINISHES

Ceiling installation.

Ceilings shall be installed in accordance with the requirements for interior wall finishes as provided in Section R702. SECTION R806 ROOF VENTILATION

Ventilation required.

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.

Minimum vent area.

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

Vent and insulation clearance.

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.

Installation and weather protection.

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.

Unvented attic and unvented enclosed rafter assemblies.

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 condition...

Attic access.

Attic access. 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).