by Cheri B.
As a building inspector, I see a lot of decks that aren't built to
code — despite the plan review process, the purpose of which
is to identify any code issues before construction commences. But
field changes are common, so an inspector is likely to find a
different deck constructed at the site than what was detailed on
Only a few provisions in the International Residential Code
specifically relate to building a deck. (The International Code
Council is currently forming a committee to develop an appendix to
the IRC that addresses deck construction.) For many specifications,
like those for spans and guardrails, you have to apply general code
Consequently, a deck contractor may not be aware that certain
changes could result in a code violation. Below are five common
reasons decks fail inspection.
No Protection Against Decay
IRC Section 319 requires all structural elements exposed to
weathering to be protected against decay, which usually means using
preservative-treated lumber (requirements can be found in IRC
It's a simple issue, usually noted on the plans and reiterated by
the permit staff, but inspectors often find a completed deck built
of standard-grade lumber. The contractor or owner must then apply
an approved on-site treatment (per IRC 319.1.1) to the open and
exposed ends and paint the rest to bring the deck into compliance
Figure 1. Untreated lumber, or
above-ground-certified lumber used in ground contact, can trigger a
failed inspection. Always check for appropriate treatment
Too Few or Inadequate Fasteners
In recent years, insufficient attachment — which includes the
use of non-weather-resistant fasteners — to the existing
structure has caused several decks to collapse. Fastener
specifications aren't usually called out on the construction plans,
and inspectors often find undersized nails, or untreated nails that
will be nothing but rust in a year.
To resist corrosion, all fasteners used in deck construction must
be hot-dipped zinc-coated galvanized steel, stainless steel,
silicon bronze, or copper. Joist hangers and anchoring straps are
subject to the same requirements as fasteners. IRC table R602.3
(1), "Fastener Schedule for Structural Members," specifies the
correct type, size, and number of fasteners required in common
construction elements (Figure 2).
Figure 2. Corrosion-resistant hardware is a
code requirement. It's doubly important when in contact with ACQ
IRC Section R502.2.2 requires positive anchoring of
non-freestanding decks to the primary structure and prohibits
toenailing or using nails to make this connection. In the 2007 IRC
Supplement, Section R502.2.2.1 was just adopted to clarify this
provision (Figure 3). It specifies the use of lag screws, or bolts
and washers when attaching the deck ledger to the primary
Figure 3. The International Code Council
adopted Table R502.2.2.1 in May 2007 (see "New Ledger Attachment
Requirements Adopted," PDB, July/August 2007). The fastener
schedule is based on research done at Virginia Tech and Washington
Inadequate or Non-approved
The IRC (Section and Table R502.5 (1)) no longer allows 4x4s or
6x6s to be used as girders (Figure 4). All structural beams and
girders must be constructed with multiple 2x4s to 2x12s, with the
depth and the number of layers of the members determined by the
span and spacing.
Figure 4. Solid lumber such as a 4x4 or a 4x6
can no longer be used as a beam. Most beams must be built up from
layers of 2-by material.
Composite decking materials are becoming very popular, but many
have been tested and approved for installation on joists spaced 12
inches on center, not 16 inches or 24 inches. You will need to
check with the individual manufacturer's specifications.
Deck joists often cantilever beyond the outer girder. The
old-school rule of thumb was that as much as one-third of the
length of the joists could cantilever beyond the beam. But about 10
years ago, the building codes reduced the allowable spans for most
softwood lumber because of declining material quality, and now
cantilevers shouldn't extend more than 24 inches beyond the beam,
unless by specific engineered design.
Insufficient Support and
Whether attached to the existing structure or freestanding, all
decks are required to be anchored against uplift and braced
laterally to prevent racking and to prevent the deck from becoming
a projectile in high winds or an earthquake.
Deck footings or piers and their posts not only support normal
loads, they also help provide the needed uplift resistance.
Concrete footings, at or below the locality's frost line, can be as
basic as a pad in the bottom to support the column, with stone
backfilled around it, or a solid-concrete pile with an anchor bolt
installed on top to hold the column in place (Figure 5).
Frost footings do more than support the
deck's downward load, they also anchor it against wind uplift. A
positive hardware connection between the footing and the deck is
Precast footings are a recent innovation (Figure 6). No holes need
to be dug for footings, as the precast blocks are set on grade, and
the posts or beams fit in pockets cast in the concrete block. To
meet the uplift anchoring requirements, straps or augers are also
required. If using precast footings, be sure to determine what
additional equipment or devices are needed.
Figure 6. Ready-made footings such as the
Dek-Block speed up the construction of free-standing decks, but
don't provide uplift resistance. Easily engineered auger and cable
tie-downs can answer that need.
Missing or Noncompliant Guardrails and
Many owners don't want a guardrail to affect the view from their
deck. They want something not too tall and often ask for benches or
planters to act as guards.
IRC Section R312 requires a guardrail for porches, balconies, or
other raised floor areas where the floor surface is more than 30
inches above the adjoining grade. Required guardrails cannot be
less than 36 inches in height. The guards are to be constructed
with infill rails or balusters no more than 4 inches apart. A bench
can be installed against a guard, but if the deck is more than 30
inches above grade, a flat bench cannot be the guard (Figure
Figure 7. Railings need be no higher behind a
bench than anywhere else, but a bench alone cannot serve as a
Porches and decks enclosed with insect screening, if 30 inches or
more above grade, must also have guards.
Handrails are not guardrails, although the terms are often thought
of at the same time. Per section R311.5.6, a handrail is required
when there are four or more risers in the stair run. When the stair
is more than 30 inches above grade or above the floor below, a
guard is also required. A compliant handrail is either circular
with a minimum 1 1/4-inch and maximum 2-inch diameter or 1 1/2
inches square (conveniently the size of a dressed 2x2).
Cheri B. Hainer is the Permits and Inspections
Administrator for the City of Virginia Beach, Va.