Introduction:
This research report provides construction details for residential deck ledger attachment to metal plate connected wood truss floor systems. The applicable codes and standards follow the 2009 and 2012 International Building Code (IBC) and the 2009 and 2012 International Residential Code (IRC). Proper attachment of the deck ledger to the house is critical for ensuring that an “attached” deck is safely and securely supported at this location. This report provides details for attaching a 2" nominal lumber deck ledger to residential floor systems constructed with metal plate connected wood (MPCW) floor trusses.
Key Definitions:
Deck Ledger – A horizontal lumber beam attached to an existing wall and used to tie in construction elements such as porch roofs and decks. A deck ledger is installed as part of the deck frame construction and supports one end of the deck joists.
Truss – An engineered structural component, assembled from wood members, metal connector plates and other mechanical fasteners, designed to carry its own weight and superimposed design loads. The truss members form a semi-rigid structural framework and are assembled such that the members form triangles.
Wood Structural Panel (WSP) – A panel manufactured from wood veneers, strands or wafers or a combination of veneer and wood strands or wafers bonded together with waterproof synthetic resins or other suitable bonding systems. Examples include: plywood, Oriented Strand Board (OSB), waferboard and composite panels.
Background:
The 2009 and 2012 IRC include prescriptive provisions for attaching a 2" nominal lumber deck ledger to a 2" nominal lumber band joist bearing directly on a sill plate or wall plate using ½"-diameter bolts or lag screws. AF&PA’s American Wood Council, in cooperation with the International Code Council, has also developed Design for Code Acceptance No. 6 (DCA6) – Prescriptive Residential Deck Construction Guide, available at awc.org. The prescriptive provisions for the deck ledger connection to the band joist in the IRC and DCA6 are based on the results from a series of ultimate load tests conducted at Virginia Polytechnic Institute and State University (VT) Department of Wood Science and Forest Products, and Washington State University (WSU) Wood Materials and Engineering Laboratory. This testing evaluated the capacity 2" nominal pressure-preservative-treated (PPT) Hem-Fir (HF) and Southern Pine (SP) ledgers attached to either 2" nominal Spruce-Pine-Fir (SPF) or 1" net Douglas-Fir (DF) laminated veneer lumber (LVL) band joists, through 15/32"-thick oriented strand board (OSB) sheathing, with ½"-diameter hot-dipped galvanized (HDG) bolts or lag screws, meeting the requirements of ANSI/ASME Standard B18.2.1.
The deck ledger assemblies evaluated at VT and WSU were deemed to represent commonly accepted means of connecting deck ledgers to band joints that cannot be evaluated using the provisions of the National Design Specification for Wood Construction (NDS) because:
1.
The ledger is not in direct contact with the band joist (i.e., separated by 15/32" OSB sheathing).2.
The minimum required penetration depth of four diameters (4D) is not met when using ½"-diameter lag screws into an 11/2"-thick band joist.
Application:
The details and fastener spacing tables provided in this report for connecting a 2" nominal lumber deck ledger to a residential floor system constructed with MPCW trusses use a single shear reference lateral design value, Z, of 710 lbs. for a ½"-diameter bolt and 375 lbs. for a ½" x 6" lag screw. These lateral design values were developed from the VT and WSU testing, and assume the fasteners are installed in accordance with the NDS requirements for clearance holes, lead holes, edge distance and end distance.
Detail 1 includes construction information for attaching 2" nominal lumber deck ledgers to the ends of MPCW floor trusses spaced no more than 24" o.c. Table 1 provides the maximum on-center spacing for each ½"-diameter bolt or ½" x 6" lag screw used to attach the ledger to the floor truss system for deck joist spans up to 18', assuming a design deck load of 40 psf live load (or 40 psf snow load) and 10 psf dead load. Table 2 includes similar information as Table 1, except for a design deck load of 60 psf live load (or 60 psf snow load) and 10 psf dead load. Detail 2 includes construction information for attaching 2" nominal lumber deck ledgers to the side of a MPCW floor ladder frame with 4x4 vertical webs spaced no more than 16" o.c. Table 3 provides the maximum on-center spacing for each ½"-diameter bolt and ½" x 6" lag screw used to attach the ledger to the ladder frame for deck joist spans up to 18', assuming a design deck load of 40 psf live load (or 40 psf snow load) and 10 psf dead load. Table 4 includes similar information as Table 3, except for a design deck load of 60 psf live load (or 60 psf snow load) and 10 psf dead load. Detail 3 includes deck lateral load connection options capable of resisting the 1500 lbf lateral load requirement specified in 2009 and 2012 IRC Section 507. Support of concentrated loads from deck beams of girders are beyond the scope of this report. Deck ledgers shall not be supported on stone or masonry veneer.
Installation:
The following is a summary of the minimum requirements and limitations for installing a 2" nominal lumber deck ledger with residential floor systems constructed with MPCW floor trusses.
1.
Ledger must be 2x10 or 2x12 PPT or code-approved decay-resistant lumber with a specific gravity, G > 0.43. Ledger shall be identified by the grade mark of, or certificate of inspection issued by, an approved lumber grading or inspection bureau or agency. PPT material must be pressure-treated with an approved process in accordance with American Wood Protection Association standards2.
Install ledger directly over wood structural sheathing (15/32" maximum thickness) fastened to the wall per the building code.3.
Attach ledger through wood structural sheathing into 2-ply 2x4 truss end vertical, 4x4 vertical web or key-block with ½" x 6" lag screws or ½"-diameter bolts with washers and nuts. 1.1
Only one (1) fastener into each truss member or key-block. 2.2
Install each fastener through the centerline of the truss member or key-block and position so as not to interfere with bottom and top chord joints and connector plates. Refer to Detail 1 and Detail 2 for spacing requirements3.3
Lag screws and bolts shall be installed according to 2005 NDS requirements. A "test" installation is recommended before drilling the lead holes, to ensure that the lead holes are neither too small nor too large.o
Lead holes for the threaded portion shall be 5/16". o
Clearance holes shall be ½" and the same depth of penetration as the length of unthreaded shank.o
Holes shall be a minimum of 17/32" to a maximum of 9/16".All fasteners used with PPT wood shall be hot-dip zinc-coated galvanized steel, stainless steel, silicon bronze, or copper. Fasteners to be hot-dipped galvanized shall meet the requirements of ASTM A153 – Standard Specification for Zinc Coating (Hot-Dip) on Iron and Steel Hardware, Class D, for fasteners 3/8" diameter and smaller or Class C for fasteners with diameters over 3/8". Lag screws, bolts, nuts and washers are permitted to be mechanically deposited zinc-coated steel with coating weights in accordance with ASTM B695, Class 55, minimum.
All hardware (e.g., joist hangers, hold-down devise, etc.) shall be galvanized or shall be stainless steel. Hardware to be hot-dipped prior to fabrication shall meet ASTM A653 – Standard Specification for Steel Sheet, Zinc-Coated (Galvanized) or Zinc-Iron Alloy-Coated (Galvannealed) by the Hot-Dip Process, G-185 coating. Hardware to be hot-dipped galvanized after fabrication shall meet ASTM A123 – Specification for Zinc (Hot-Dip Galvanized) Coatings on Iron and Steel Products.
Fasteners and hardware exposed to saltwater or located within 300' of a salt water shoreline shall be stainless steel grade 304 or 316.
Fasteners and hardware shall be of the same corrosion-resistant material.
Other coated or non-ferrous fasteners or hardware shall be as approved by the authority having jurisdiction.4.
Install flashing at top of ledger for water tightness. Flashing shall be corrosion-resistant metal of minimum nominal 0.019" thickness or an approved non-metallic material. Do not use aluminum flashing in direct contact with lumber treated with preservatives containing copper, such as ACQ, Copper Azole or ACZA.5.
Two-ply 2x4 truss end verticals, 4x4 truss vertical webs and key-blocks connected to ledger with lag screws or bolts shall have a specific gravity, G ≥ 0.42 (includes DF, HF, SP and SPF).
Construct key-blocks with minimum 2x4 No. 2 or better lumber.
Install key-blocks at required locations. Cut to fit tight.
Refer to Detail 1 and Detail 2 for additional information concerning key-block construction and attachment.
Detail 1: Attachment of Deck Ledger to Floor System with MPCW Trusses (See PDF for Figure)
Joist Span | < to 6' | 6'-1" to 8' | 8'-1" to 10' | 10'-1" to 12' | 12'-1" to 14' | 14'-1" to 16' | 16'-1" to 18' |
Connection Details | On-center Spacing of Fasteners (in.)4 |
½"x 6" lag screw with 15/32",max., wood structural panel sheathing | 24 | 125 | 125 | 125 | 125 | 86 | 86 |
½" diameter bolt with 15/32", max., wood structural panel sheathing | 24 | 24 | 24 | 24 | 24 | 125 | 125 |
Ledgers shall be flashed in accordance with applicable building code requirements to prevent water from contacting the exposed wood structural sheathing and floor truss. Snow load shall not be assumed to act concurrently with live load. Ledgers must be 2x10 or 2x12 PPT or code-approved decay-resistant lumber with specific gravity, G > 0.43. Truss 2-ply 2x4 end verticals and key-blocks must have a G > 0.42. Stagger lag screws and bolts as shown in Detail 1. Requires key-blocks at 24" o.c., maximum. Attach ledger to 2-ply end vertical of each truss with one (1) fastener and to each key-block with one (1) fastener. Refer to Detail 1 for key-block construction and installation information. Requires two (2) key-blocks at 8" o.c., maximum, between each truss. Attach ledger to 2-ply end vertical of each truss with one (1) fastener and to each key-block with one (1) fastener. Refer to Detail 1 for key-block construction and installation information. |
Table 1: Deck Ledger Connection to Ends of MPCW Floor Trusses Spaced 24" o.c., Max.1,2,3
(Deck Live Load = 40 psf, Deck Dead Load = 10 psf, Snow Load 40 psf)
Joist Span | < to 6' | 6'-1" to 8' | 8'-1" to 10' | 10'-1" to 12' | 12'-1" to 14' | 14'-1" to 16' | 16'-1" to 18' |
Connection Details | On-center Spacing of Fasteners (in.)4 |
½" x 6" lag screw with 15/32",max., wood structural sheathing | 125 | 125 | 125 | 86 | 86 | 86 | Use bolted connection |
½" diameter bolt with 15/32", max., wood structural sheathing | 24 | 24 | 24 | 125 | 125 | 125 | 125 |
1. Ledgers shall be flashed in accordance with applicable building code requirements to prevent water from contacting the exposed wood structural sheathing and floor truss. 2. Snow load shall not be assumed to act concurrently with live load. 3. Ledgers must be 2x10 or 2x12 PPT or code-approved decay-resistant lumber with specific gravity, G > 0.43. Truss 2-ply 2x4 end verticals and key-blocks must have a G > 0.42. 4. Stagger lag screws and bolts as shown in Detail 1. 5. Requires key-blocks at 24" o.c., maximum. Attach ledger to 2-ply end vertical of each truss with one (1) fastener and to each key-block with one (1) fastener. Refer to Detail 1 for key-block construction and installation information. 6. Requires two (2) key-blocks at 8" o.c., maximum, between each truss. Attach ledger to 2-ply end vertical of each truss with one (1) fastener and to each key-block with one (1) fastener. Refer to Detail 1 for key-block construction and installation information. |
Table 2: Deck Ledger Connection to Ends of MPCW Floor Trusses Spaced 24" o.c., Max.1,2,3
(Deck Live Load = 60 psf, Deck Dead Load = 10 psf, Snow Load < 60 psf)
(See PDF for Figure)
Detail 2: Attachment of Deck Ledger to Floor System with MPCW Trusses,
When Ledger is Installed Parallel to Truss Span & Spacing of Screws is Less Than the Spacing of the Verticals
Joist Span | < 6' to 8' | 8'-1" to 10' | 10'-1" to 12' | 12'-1" to 14' | 14'-1" to 16' | 16'-1" to 18' |
Connection Details | On-center Spacing of Fasteners (in.)4 |
½" x 6" lag screw with 15/32",max., wood structural sheathing | 16 | 16 | 85 | 85 | 85 | 85 |
½" diameter bolt with 15/32", max., wood structural sheathing | 32 | 32 | 16 | 16 | 16 | 16 |
1. Ledgers shall be flashed in accordance with applicable building code requirements to prevent water from contacting the exposed wood structural sheathing and floor truss. 2. Snow load shall not be assumed to act concurrently with live load. 3. Ledgers must be 2x10 or 2x12 PPT or code-approved decay-resistant lumber with specific gravity, G > 0.43. Truss 4x4 vertical web and key-blocks must have a G > 0.42. 4. Stagger lag screws and bolts as shown in Detail 2. 5. Requires key-blocks at 16" o.c., maximum. Attach ledger to each 4x4 vertical web with one (1) fastener and to each key-block with one (1) fastener. Refer to Detail 2 for key-block construction and installation information. |
Table 3: Deck Ledger Connection to Side of MPCW Floor Ladder Frame with 4s4 Vertical Webs Spaced at 16" o.c., Max.1,2,3
(Deck Live Load = 40 psf, Deck Dead Load = 10 psf, Snow Load 40 psf)
Joist Span | < 6' to 8' | 8'-1" to 10' | 10'-1" to 12' | 12'-1" to 14' | 14'-1" to 16' | 16'-1" to 18' |
Connection Details | On-center Spacing of Fasteners (in.)4 |
½" x 6" lag screw with 15/32",max., wood structural sheathing | 16 | 85 | 85 | 85 | 85 | Use bolted connection |
½" diameter bolt with 15/32", max., wood structural sheathing | 32 | 16 | 16 | 16 | 85 | 85 |
1. Ledgers shall be flashed in accordance with applicable building code requirements to prevent water from contacting the exposed wood structural sheathing and floor truss. 2. Snow load shall not be assumed to act concurrently with live load. 3. Ledgers must be 2x10 or 2x12 PPT or code-approved decay-resistant lumber with specific gravity, G > 0.43. Truss 4x4 vertical web and key-blocks must have a G > 0.42. 4. Stagger lag screws and bolts as shown in Detail 2. 5. Requires key-blocks at 16" o.c., maximum. Attach ledger to each 4x4 vertical web with one (1) fastener and to each key-block with one (1) fastener. Refer to Detail 2 for key-block construction and installation information. |
Table 4: Deck Ledger Connection to Side of MPCW Floor Ladder Frame with 4x4 Vertical Webs Spaced at 16" o.c., Max.1,2,3
(Deck Live Load = 60 psf, Deck Dead Load = 10 psf, Snow Load 60 psf)
(See PDF for Figure)
Detail 3: Deck Lateral Load Connection Capable of Resisting the 1500 lbf Lateral Load Requirement
Specified in 2009 & 2012 IRC Section 507 1.
