Building a deck seems to be as American as eating apple pie.
While the general way a deck is built hasn't changed too much
over the years, the details involved in the construction have.
The Code has very specific requirements for railings (guards),
stairs and handrails, and very specific hardware is now required
due to changes in the chemistry of treated lumber.
Deck Construction
Town of Marcellus Code Enforcement Office
Town of Marcellus, 24 East Main Street, Marcellus, NY 13108
The Chemistry
Nearly 40 million lb. of arsenic was being used in this country every year,
and most of it went into the pressure-treated wood used to build decks
and playgrounds. But that all changed January 1, 2004.
The Environmental Protection Agency (EPA) banned chromated copper
arsenate (CCA) as a preservative for wood intended for residential use
(except for the lumber that is used in permanent wood foundations).
There's no need to panic about existing CCA-treated structures.
The EPA says that they're fine. But if you're nervous about the chances of
leaching chromium and arsenic, you can make your deck or swing set safer
by coating it with an oil-based penetrating stain every couple of years.
To make the new preservatives effective, their copper content has been
boosted substantially -- from around 18% to 96% in some cases. Because
ACQ and copper azole contain so much more copper, you can expect to
pay from 15% to 35% more than you paid for CCA lumber. The cost varies
because the amount of chemical treatment varies. CCA wasn't that expensive,
so most CCA lumber was given a maximum dose of preservatives and rated
for ground contact.
To keep down the cost of the new pressure-treated wood, manufacturers will
produce different levels of protection (chemical-retention levels) for different
end uses. End-use categories will be marked on the tags stapled to the end
of the board, but in general, they'll be determined by the dimension of the
lumber itself. The lowest chemical-retention level will be for 5/4 stock, or
decking. One level higher will be 2x lumber, or above ground. Ground contact
will be 4x and 6x lumber, and other stock will be treated for permanent wood
foundations (PWF, or structural members).
The Footings
Most decks are constructed with either ground contact treated lumber posts
resting on concrete footings below the frostline or on concrete piers.
If a deck is attached to the house the postholes must be 42-inches deep.
If a deck is NOT attached to the house the postholes must be 42-inches deep
OR all vertical supports must be crossed-braced.
The depth of the postholes must be inspected by the Code Enforcement Officer
prior to filling the holes.
The Framing
Unfortunately, boosting the copper content in lumber not only makes the
new pressure-treated wood more expensive than the old, but it also makes
the new stuff significantly more corrosive -- 5 times more to common steel,
according to American Wood Preservers Association (AWPA) test results.
As a result different coatings on the hardware must be used.
The new arsenic-free alkali-based treated lumber is highly corrosive and will
eat through the standard galvanized nails and joist hangers resulting in the
possible failure of the deck framing. Stainless steel hardware is the best
but also the most expensive.
In leu using of stainless steel, all nails and connectors (bolts) must be double hot-dipped galvanized.
These fasteners have a dull grey finish.
Joist hangers and other metal hardware must also be double hot-dipped galvanized or of other approved materials.
Hardware approved for use with ACQ typically has a model number that includes or ends in a "Z".
Unapproved screws are not alllowed in
joist hangers or other hardware.
Screws are not alllowed in joist hangers
and hangers must be tight against the
sides of the joist.
X
ü
Joist hangers, post bases and all
other hardware must be installed
using approved fasteners.
Approved fasteners typically
include double hot-dipped
galvanized10d and 12d
common nails. Deck screws,
drywall screws and roofing
nails are prohibited.
The manufacturers agree:
Never use galvanized deck
screws or drywall screws
to install joist hangers.
Those screws don’t have
the shank size and toughness
to support joist loads.
Install the largest hanger that
fits the lumber. Never use a 2x6
hanger on a 2x10 joist. Avoid
disaster by spending a couple
of bucks more for the correct
joist hanger.
Hot-dipped galvanized bolts
must always be used in beam
and post assemblies.
Deck screws are never
acceptable for supporting the
loads carried by beams.
X
X
The bolt on the left is hot-dipped galvanized.
The bolt on the right is standard galvanized.
On decks attached to a house,
the ledger must be attached
with lag or through bolts into
the structural framing of the house.
Flashing must be properly installed
above the ledger. Perhaps the most
important point to keep in mind
relating to copper-based wood
treatments and galvanic corrosion
is to avoid aluminum flashings
altogether. Aluminum corrodes
quickly in the presence of high
copper concentrations.
for double hangers, use 8d or 10d nails. For double shear single hangers, fasten the hanger to the joists with
longer 8d or 10d nails. This type of hanger requires fewer but longer nails for the side flanges. The nails
penetrate into the wall ledger and therefore offer both better joist load capacity than standard-duty hangers
and more protection against uplift forces caused by wind.
The Stairs
The Handrail
