§ 27-623 Heavy timber construction (construction class II-A).
AC § 27-623
(a)Minimum sizes of members. To conform to the fire resistance rating requirements for heavy timber construction (construction class II-A), members shall be solid sawn or solid glue-laminated and of the following minimum dimensions: (Sizes of wood members indicated in this section are nominal sizes).
(1)COLUMNS, FRAMES AND ARCHES. a. Columns shall be at least eight inches in all dimensions when supporting floor loads, and at least six inches wide and eight inches deep when supporting roof and ceiling loads only. b. Beams and girders shall be at least six inches wide and ten inches deep. c. Frames or arches that spring from grade or the floor line and support floor loads shall be at least eight inches in all dimensions. d. Timber trusses supporting floor loads shall have members at least eight inches in all dimensions. e. Frames or arches for roof construction that spring from grade or the floor line and do not support floor loads shall have members at least six inches wide and eight inches deep for the lower half of the height, and at least six inches deep for the upper half. f. Frames or arches for roof construction that spring from the top of walls or wall abutments, framed timber trusses, and other roof framing, which do not support floor loads, shall have members at least four inches wide and six inches deep. Spaced members may be composed of two or more pieces at least three inches thick when blocked solidly through their intervening spaces or when such spaces are tightly closed by a continuous wood cover plate at least two inches thick secured to the underside of the members. Splice plates shall be at least three inches thick. When protected by approved automatic sprinklers under the roof deck, framing members shall be at least three inches wide.
(2)FLOORS. a. Planks shall be splined or tongue-and-groove, not less than three inches thick, covered with one inch tongue-and-groove flooring, laid crosswise or diagonally to the plank, or other surface having equivalent fire resistance; or shall be, b. At least four inches wide, set on edge close together and well spiked, and covered the same as for three inch thick plank. The planks shall be laid so that there is no continuous line of end joints except at points of support. Floors shall not extend closer than one-half inch to walls to provide an expansion joint, but the joint shall be covered at top or bottom to avoid flue action.
(3)ROOF DECKS. Roof decks shall be splined or tongue-and-groove planks at least two inches thick; or tongue-and-groove plywood panels (bonded with exterior glue) at least one and one-eighth inch thick, with face grain perpendicular to supports that shall be spaced not more than forty-eight inches on center; or of planks at least three inches wide set on edge close together and laid as required for floors.
(b)Construction details. Self releasing type wall plate boxes or approved hangers shall be provided where beams and girders enter masonry. Table 10-4Nailing Schedule Building Element Nail Type Number and Distribution Stud to sole plateCommon-toe-nail4 – 8d Stud to cap plateCommon-end-nail2 – 16dDouble studsCommon-direct10d 12 in. o. c. or 16d 30 in. o.c.Corner studsCommon-direct16d 30 in. o.c.Sole plate to joist or blockingCommon16d 16 in. o.c.Double cap plateCommon-direct16d 24 in. o. c.Cap plate lapsCommon-direct3 – 16dRibbon strip, 6 in. or lessCommon-direct2 – 10d each bearingRibbon strip, over 6 in.Common-direct3 – 10d each bearingRoof rafter to plateCommon-toe-nail3 – 16dRoof rafter to ridgeCommon-toe-nail2 – 16dJack rafter to hipCommon-toe-nail3 – 10dFloor joists to studs (no ceiling joists)Common-direct5 – 10d or 3 – 16dFloor joists to studs (with ceiling joists)Common-direct2 – 10dFloor joists to sill or girderCommon-toe-nail2 – 16dDouble-joist to joistCommon-direct10d – staggered at 16 in.Ledger stripCommon-direct3 – 16d at each joistCeiling joists to plateCommon-toe-nail2 – 16dCeiling joists to every rafterCommon-direct(See table below)Ceiling joists (laps over partitions)Common-direct3 – 16dCollar beamCommon-direct4 – 10dBridging to joists and raftersCommon-direct2 – 8d each endBridging to studsCommon-direct or toe2 – 10d each endDiagonal brace (to stud and plate)Common-direct2 – 8d each bearingTail beams to headers (when nailing permitted)Common-end1 – 20d each 4 sq. ft. floor areaHeader beams to trimmers (when nailing permitted)Common-end1 – 20d each 8 sq. ft. floor area1 in. Subflooring (6 in. or less in width)Common-direct2 – 8d each joist1 in. Subflooring (over 6 in. in width)Common-direct3 – 8d each joist2 in. SubflooringCommon-direct2 – 20d each joist1 in. Wall sheathing (8 in. or less in width)Common-direct2 – 8d each stud1 in. Wall sheathing (over 8 in. in width)Common-direct3 – 8d each studPlywood sheathing and subflooring a 1 in. Roof sheathing (6 in. or less in width)Common-direct2 – 8d each rafter1 in. Roof sheathing (over 6 in. in width)Common-direct3 – 8d each rafterShingles, woodCorrosion-resistive2 – No. 15 B&S each bearingWeather boardingCorrosion-resistive2 – 8d each bearing1/2 in. Fiberboard sheathing1 1/2 in. galvanized roofing nail 6d common nail 16 ga. galvanized staples, 1 1/8 in. long, 7/16 in. crown3 in. c. c. on all edges and6 in. c. c. at other bearings25/32 in. Fiberboard sheathing1 3/4 in. galvanized roofing nail 8d common nail 16 ga. galvanized staples, 1 1/2 in. long, 7/16 crown3 in. c. c. on all edges and 6 in. c. c. at other bearings1/2 in. Gypsumboard sheathing1 1/2 in. galvanized roofing nail 11 ga., 3/8 in. to 7/16 in. head 16 ga. galvanized staples, 1 1/2 in. long, 7/16 crown4 in. c. c. on all edges and 8 in. c. c. at other bearings Note a. For nailing of plywood, see reference standard RS 10-9. CEILING JOIST NAILING TO EVERY RAFTER(Number of 16d nails) Slope of Roof 4/125/126/127/12 9/1212/12 Rafter Spacing, o.c. (in.)16 24 16 24 16 24 16 24 16 24 16 24 Width of building Up to 24 ft.584735343333 24 to 30 ft.7116947363433
