CHAPTER 8 ROOF-CEILING CONSTRUCTION - …

1 CHAPTER 8 ROOF-CEILING CONSTRUCTIONSECTION provisions of this CHAPTER shall con-trol the design and CONSTRUCTION of the ROOF-CEILING system forall and ceiling CONSTRUCTION shall becapable of accommodating all loads imposed according to Sec-tion R301 and of transmitting the resulting loads to the support-ing structural roof areas where expansive or collaps-ible soils are known to exist, all dwellings shall have a con-trolled method of water disposal from roofs that will collectand discharge all roof drainage to the ground surface at least 5feet (1524 mm) from foundation walls or to an approved drain-age R802 WOOD roof dimension lumber forrafters, trusses and ceiling joists shall be identified by a grademark of a lumber grading or inspection agency that has beenapproved by an accreditation body that complies with DOC PS20.

2 In lieu of a grade mark, a certificate of inspection issued bya lumber grading or inspection agency meeting the require-ments of this section shall be shall be a minimum of utilitygrade End-jointed end-jointed lum-ber identified by a grade mark conforming to may be used interchangeably with solid-sawn mem-bers of the same species and Fire-retardant-treated wood is any wood product which, when impregnatedwith chemicals by a pressure process or other means duringmanufacture, shall have, when tested in accordance withASTM E84, a listed flame spread index of 25 or less andshow no evidence of significant progressive combustionwhen the test is continued for an additional 20-minute pe-riod.

3 In addition, the flame front shall not progress morethan feet (3200 mm) beyond the center line of the burn-ers at any time during the lumber andwood structural panels shall be labeled. The label shallcontain:1. The identification mark of an approved agency inaccordance with Section of the NorthCarolinaBuilding Identification of the treating The name of the fire-retardant The species of wood Flame spread and smoke developed Method drying after Conformance with appropriate standards in accor-dance with Sections For FRTW exposed to weather, damp or wet loca-tion, the words No increase in the listed classifi-cation when subjected to the Standard Rain Test (ASTM D2898).

4 Strength values foruntreated lumber and wood structural panels as specifiedin Section , shall be adjusted for fire retardant-treated wood. Adjustments to design values shall bebased upon an approved method of investigation whichtakes into consideration the effects of the anticipatedtemperature and humidity to which the fire-retar-dant-treated wood will be subjected, the type of treat-ment and redrying Wood structural effect oftreatment and the method of redrying after treatment,and exposure to high temperatures and highhumidities on the flexure properties of fire-retar-dant-treated softwood plywood shall be determinedin accordance with ASTM D 5516.

5 The test data de-veloped by ASTM D 5516 shall be used to developadjustment factors, maximum loads and spans, orboth for untreated plywood design values in accor-dance with ASTM D 6305. Each manufacturer shallpublish the allowable maximum loads and spans forservice as floor and roof sheathing for their each species of woodtreated the effect of the treatment and the methodofredrying after treatment and exposure to high tem-peratures and high humidities on the allowable designproperties of fire-retardant-treated lumber shall bedetermined in accordance with ASTM D 5664. Thetest data developed by ASTM D 5664 shall be used todevelop modification factors for use at or near roomtemperature and at elevated temperatures and humid-ity in accordance with an approved method of investi-gation.

6 Each manufacturer shall publish themodification factors for service at temperatures of notless than 80 F ( C) and for roof framing. Theroof framing modification factors shall take into con-sideration the climatological Exposure to fire-retar-dant-treated wood is exposed to weather, or damp or wetlocations, it shall be identified as Exterior to indicatethere is no increase in the listed flamespread index as de-fined in Section when subjected to ASTM NORTH CAROLINA RESIDENTIAL Interior fire-retardant-treated wood shall have a moisture content ofnot over 28 percent when tested in accordance withASTM D 3201 procedures at 92 percent relative humid-ity.

7 Interior fire-retardant-treated wood shall be tested inaccordance with Section or fire-retardant-treated wood designated as TypeA shall be tested in accordance with the provisions of Moisture shall be dried to a moisture content of 19 percent orless for lumber and 15 percent or less for wood structuralpanels before use. For wood kiln dried after treatment(KDAT) the kiln temperatures shall not exceed thoseused in kiln drying the lumber and plywood submittedfor the tests described in Section for ply-wood and for Structural glued laminated timbers shall be manufactured and identified asrequired in AITC and ASTM Design and shall be de-signed and constructed in accordance with the provisions ofthis CHAPTER and Figures (1), (2) (3) or in accordance with AFPA/NDS.

8 Components ofroof-ceilings shall be fastened in accordance with (1). Framing shall be framed to ridgeboard or to each other with a gusset plate as a tie. Ridge boardshall be at least 1-inch ( mm) nominal thickness and notless in depth than the cut end of the rafter. At all valleys and hipsthere shall be a valley or hip rafter not less than 2-inch (51 mm)nominal thickness and not less in depth than the cut end of therafter. Hip and valley rafters shall be supported at the ridge by abrace to a bearing partition or be designed to carry and distrib-ute the specific load at that point. Where the roof pitch is lessthan three units vertical in 12 units horizontal (25-percentslope), structural members that support rafters and ceilingjoists, such as ridge beams, hips and valleys, shall be designedas ceiling joist and rafter and rafters shall be nailed to each other in accordancewith Tables (1) and (9), and the assemblyshall be nailed to the top wall plate in accordance with (1).

9 ceiling joists shall be continuous or securelyjoined where they meet over interior partitions and nailed toadjacent rafters to provide a continuous tie across the build-ing when such joists are parallel to the ceiling joists are not parallel to rafters,subflooring or metal straps attached to the ends of the raftersshall be installed in a manner to provide a continuous tieacross the building, or rafters shall be tied to 1-inch by4-inch ( mm by 102 mm) (nominal) minimum-sizecrossties. The connections shall be in accordance with (1) or connections of equivalent capacities shall beprovided. Where ceiling joists or rafter ties are not providedat the top plate, the ridge formed by these rafters shall alsobe supported by a girder designed in accordance with ac-cepted engineering ties shall be spaced not more than 4 feet (1219 mm)on 1-inch by6-inch (25 mm 152 mm) or 2-inch by4-inch (51 mm 102 mm) collar beam shall be nailed in theupper third of the roof to every third pair of rafters not to ex-ceed 4 feet on center.

10 Collar beams shall be connected to therafters as specified in Table (1) for rafter ceiling joists of ceiling joists shallbe lapped a minimum of 3 inches (76 mm) or butted overbearing partitions or beams and toenailed to the bearingmember. When ceiling joists are used to provide resistanceto rafter thrust, lapped joists shall be nailed together in ac-cordance with Table (1) and butted joists shall betied together in a manner to resist such Allowable ceiling joist for ceiling joistsshall be in accordance with Tables (1) and (2).For other grades and species and for other loading conditions,refer to the AF&PA Span Tables for Joists and Allowable rafter for rafters shall be inaccordance with Tables (1) through (8).