Of physical safety, efficiency, convenience,
durability, and aesthetics — safety
rules.Before The Architect
INTRODUCTION
article is
about crucial safety in design and construction of deck ledger attachment.
a swell
way to wreck a deck? Break things? Hurt people?
attach
the ledger to house structure and the deck structure to the ledger.
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
bolts
shall be applied as fasteners for a ledger to house structure
galvanized – bolt, washers, and nut
not less
than 5/8 linear inch diameter
not
greater than 16 linear inches on center, preferably not greater than
12 linear inches on center
pre-drilled holes not less than 1/32 linear inch and not greater
than 1/16 linear inch larger than bolt diameter
to barely pock the ledger face exposed around the washer
galvanized
lag screws must be used instead of carriage bolts, then
2 such
screws shall be applied sequentially
screw
shall penetrate
less than the depth of the in-lieu
less than 1/2 linear inch clear-through where applicable
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
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
screw
shall be run home
wrenching and not by hammering
more than 1 such screw shall be applied in a 4 linear feet span
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.
any case –
whether screw or bolt
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.
to
which newer preservatives shall include
of aluminum flashing
optionally of either stainless steel or copper flashing
that if borate
(a/k/a DOT, or disodium octaborate tetrahydrate) is the wood preservative
wood so
preservative-treated shall be applied only in persistently dry areas,
e.g., most mudsills or sill plates, unless otherwise noted and
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
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
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.
structure
and fasteners shall be protected from natural moisture by
only
preservative-treated lumber
flashing
not
less than 6 linear inches concealed between superior sheathing and
house wrap to
90° turn
to cover the ledger top of face and abut to the structure to which
it is fastened and
from
the exterior side of face of the ledger not less than 2 linear
inches and at approximately a 45° deflection downward
to
thoroughly seal bolts and screws and their washers from moisture
intrusion
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.
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 The Journal of Light Construction,
notably addressing “Detail 4: Deck Building Supported with Posts" and related
text.
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