This article is about crucial safety in design and construction of deck ledger attachment.
Know a swell way to wreck a deck? Break things? Hurt people?
Poorly attach the ledger to house structure and the deck structure to the ledger.
Interested in securely attaching a deck to a house? Please read on. This is about NOT breaking things and NOT hurting people.
HOME DECK DESIGN SAFETY, ATTACHING DECK TO HOUSE
Carriage bolts shall be applied as fasteners for a ledger to house structure
Apply galvanized – bolt, washers, and nut
At not less than 5/8 linear inch diameter
At not greater than 16 linear inches on center, preferably not greater than 12 linear inches on center
Into pre-drilled holes not less than 1/32 linear inch and not greater than 1/16 linear inch larger than bolt diameter
Tightened to barely pock the ledger face exposed around the washer
When galvanized lag screws must be used instead of carriage bolts, then
No 2 such screws shall be applied sequentially
Such screw shall penetrate
Not less than the depth of the in-lieu
Not less than 1/2 linear inch clear-through where applicable
In a hole predrilled to unthreaded depth and in diameter not less than 1/32 linear inch and not greater than 1/16 linear inch larger than the unthreaded shank’s diameter
In a hole predrilled for the threaded depth in diameter not less than 1/32 linear inch and not greater than 1/16 linear inch narrower than the threaded shank’s root diameter
Such screw shall be run home
By wrenching and not by hammering
Not more than 1 such screw shall be applied in a 4 linear feet span
Tightened to barely pock the ledger face exposed around the washer
Comment: This designer might relax this last guidance about lag screw spacing where a deck is fastened to structure on more than one side. All other design and construction guidance herein under in regard to attaching a deck to house structure prevails as is.
In any case – whether screw or bolt
Shall be in conformance with not less than applicable standards in the Fastening Design Standards, section head below, GENERAL SPECIFICATIONS FOR FASTENERS TO MEMBERS PRESERVATIVE-TREATED W/ ALKALINE COPPER QUAT (ACQ Types A and B), COPPER AZOLE (CBA-A & CA-B). etc. applicable to wood deck members, mudsills and other members in contact with concrete, e.g., pocketed beams, floor joists, floor trusses, etc. or subject to atmospheric exposure, e.g., porch posts, framing lumber, plywood, furring strips, mouldings, etc.
Adaptation to which newer preservatives shall include
Prohibition of aluminum flashing
Application optionally of either stainless steel or copper flashing
Note that if borate (a/k/a DOT, or disodium octaborate tetrahydrate) is the wood preservative
The wood so preservative-treated shall be applied only in persistently dry areas, e.g., most mudsills or sill plates, unless otherwise noted and
No special materials are required either to coat or comprise the fasteners, flashings, etc. beyond those applied either to untreated lumber or CCA (chromated copper arsenate)-treated lumber
In any case – whether screw or bolt – ledger shall be offset to structure ½ linear inch by stacked washers over moisture impermeable barrier material
Comment: For a larger view of wood preservation variously treated, this house designer suggests you consider “Wood Preservation" by Rebecca E. Ibach at http://www.treesearch.fs.fed.us/pubs/7156
Support shelves set below ledgers, joists, beams, etc. shall not be considered structure
Wooden Deck Ledger, Elevation and Section in Elevation
Comment: “Rim board" here is not meant to identify genuine 2 linear inches x dimensioned lumber applied as end and head joists, or “ribbon", or “band". Rim board here is meant to identify anything that isn’t 2 linear inches x dimensioned lumber applied as end and head joist, or “ribbon", etc….that specifically means OSB and other particle-component building materials. These materials, unamended by substantially incremental structure, are, in the AG’s opinion, unsuitable for direct support of ledgers.
Ledger structure and fasteners shall be protected from natural moisture by
Applying only preservative-treated lumber
Continuous flashing
From not less than 6 linear inches concealed between superior sheathing and house wrap to
A 90° turn to cover the ledger top of face and abut to the structure to which it is fastened and
Away from the exterior side of face of the ledger not less than 2 linear inches and at approximately a 45° deflection downward
Caulking to thoroughly seal bolts and screws and their washers from moisture intrusion
Offsetting ledger from exterior wall by not more than ½ linear inch by applying galvanized washers as shims – see www.jlconline.com/deckledgers
Joist and beam hangers to ledger shall not be less than in full-depth specification in conformance to joist and beam nominal depth, absolutely
Comment: “Short" hangers distribute joist and beam weight unevenly to the ledger, relying on only a part – a lower part – of the ledger for support.
This is analogous to an unsupported back-cut into a joist at a plate or beam joint, or resting a rafter heal interior to a double top plate top of face. Air is not a structure. Immediately above, the illustration of a ledger specification reflects our ledger design standards.
A particle rim board shall be a prohibited material for fastening a ledger without express compensations to structure as developed by a qualified engineer or, in some cases, a master carpenter
Comment: If this ledger design guidance is not practical in application - notably, for some house remodeling projects- please consider this alternative method of deck construction, see “Attaching Deck Ledgers" by Cheryl Anderson, Frank Woeste, and Joe Loferski in the August 2003 issue of Journal of Light Construction, notably addressing “Detail 4: Deck Building Supported with Posts" and related text.
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information presented herein intended to substitute for the advice provided to you by any health care or other professional
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