Insight on engineering and codes
Alternative Ledger Connections
Over the last year there's been a lot of discussion about the new
ledger bolting table and lateral load detail in the 2009
International Residential Code (IRC). I thought I would break out
of the box a little bit and talk about some other ways and places a
ledger can be supported and how the IRC may be able to help. Let's
move away from the band joist connection and away from a
black-and-white interpretation of the IRC, to add some freedom and
design flexibility to your bag of tricks. And while what I'm about
to cover isn't a "don't try this at home" kind of thing, make sure
to get your plans approved by the local jurisdiction before
Can Studs Handle the Load?
So how smart do you think studs are? Will they know the difference
between a vertical live load from a deck and vertical dead load
from masonry? IRC section R703.7.2.1 provides criteria for
attaching an angle iron lintel to wood studs for the purpose of
supporting brick veneer. Why can't the same loading be used to
engineer a deck ledger attachment?
A steel angle connected to double 2x4 studs at 16 inches on center
with two 7/16-inch x 4-inch lag screws can carry 40 pounds per
square foot (psf) of brick veneer to a height of 12 feet 8 inches.
Because the doubled studs act like a single larger member, the
large-diameter lag screw can get complete penetration into the wood
fibers without splitting out the side.
From these criteria, the vertical loads placed at the face of
double 2x4 studs can be easily determined. At 40 psf and 12 feet 8
inches of allowable height, the bolting prescribed by the IRC is
supporting 480 pounds per linear foot of dead load. So, if a bolted
lintel can handle 480 pounds per lineal foot, you can equate it to
a deck load by dividing by 50 psf, the minimum combined live and
dead load of deck. That yields a potential 10 square feet of deck
supported by each foot of ledger. Because only half the load of a
deck is borne by the ledger (the outer beam carries the other
half), this is equivalent to a deck with a 20-foot joist span, far
greater than typical.
One argument against this interpretation may be that floors
supporting an occupant load would have a safety factor built in to
the prescriptive criteria and that brick veneer loads would not. If
that were the case, the standard 2.5 safety factor for testing of
assemblies would certainly be appropriate. With that consideration,
you could still have an 8-foot span between bearing points. This
would be very conservative, but should be easily acceptable.
We aren't finished with the analysis though, as only the magnitude
of the load has been equated. Next we have to consider the
replacement of a steel angle with a 2-by wood ledger. While the
fastener securing two materials together is almost always
questioned by builders and inspectors, it is often the wood member
in the connection that is the limiting factor. The fastener strains
the internal integrity of wood members with as much force as is
applied to it. In the race to failure, the wood usually loses -
that is, the wood is likely to fail before the bolt.
Consider a generic bolted connection between two pieces of wood
using eight bolts. The same connection made with only four bolts
that were twice as strong would not necessarily be equal. The force
on the wood around the bolts is doubled, increasing the likelihood
of wood failure even though the four stronger bolts are capable of
supporting the same load as the eight weaker ones.
You can't arbitrarily swap wood for metal without evaluating the
force imposed by the fasteners on the wood, a job for an engineer.
However, in this application, we know from the IRC's ledger bolting
table that wood ledgers handle internal stresses just fine when
secured with bolts every 16 inches. In this case, swapping wood for
metal doesn't really make a difference.
Another item for consideration is the length of the lag bolt
penetration into the studs. The steel angle is only about 1/4 inch
to 3/16 inch thick, as opposed to the 11/2-inch-thick ledger, so
adding about 11/4 inches to the length of the 4-inch bolts is in
The most difficult part of this connection method is the need for
double studs, which are not typical in most walls. On new
construction, it's easy enough to add studs. But on an existing
house, you will likely find doubles only at corners and at the
sides of windows and doors. So, while this solution may not work
for all applications, it does provide some design freedom in
others. For instance, if the deck is outside an unfinished walkout
or garden-level basement, or a garage, then adding some studs may
Connection to a Foundation
In my former career as a deck builder, I bolted many decks to
concrete foundations. I am sure many of you have done the same.
There are lots of good reasons to do this; for one, it provides a
step down to the deck, which limits the amount of snow that can
build up around the door. And dropping the deck also "lowers the
stage" from all the neighbors. Often just a few feet can make the
difference between seeing over a privacy fence or not.
Connecting a ledger to a foundation also allows you to avoid the
extra beam and footings required for a freestanding deck,
simplifying the framing. A landing or a small upper deck will take
care of the step at the door. Though I was never questioned about
it during inspections, I wouldn't have known a way to back it up by
the code. Now that we have a ledger bolting table in the IRC,
equivalent methods can be submitted with little effort.
There are only a few differences between ledger connection to band
joists and to concrete. The only criteria I see needing evaluation
are the fastener shear strength, the fastener connection strength,
and the internal strength of the concrete. Manufacturers like ITW
Red Head (630/350-0370, www.itwredhead.com), Simpson Strong-Tie (800/999-5099,
www.strongtie.com), and USP (800/328-5934,
uspconnectors.com) know that for their products to sell, they have
to be tested so limitations of use can be provided to consumers and
designers. Testing is one way to approval as an alternative to the
code. Combining these tested connections with the ledger table in
the code shouldn't be a problem at all.
What About Lateral Loads?
With the addition of the lateral load anchor detail to the 2009 IRC
(see Structure, November 2009; www.deckmagazine.com), it's hard to say whether the
bolts in the ledger table are given any credit for resisting
lateral loads. While failing band joists were the reason for the
detail, many folks will read the 2009 IRC and discredit all lateral
restraint from ledger bolts: "Why would the lateral anchor detail
be there if the ledger bolts could resist the loads?"
The history of successful bolted connections tells me lags are
worth something in the battle against lateral loads. I've never
heard of a deck ledger whose properly installed lag bolts pulled
straight out of the fibers of the band joist. Lag screws have
listed withdrawal capacities in the NDS (National Design
Specification for Wood Structures, a referenced standard of the IRC
and IBC) of around 400 pounds per inch of penetration in Douglas
fir. The problem isn't the ledger-to-band-joist connection, but the
one between the band joist and the house. If the band joist is the
problem, I think bolting to the studs or using concrete anchors of
comparable strength is a perfectly fine way to achieve lateral load
resistance - one lag fully penetrating a 2x4 stud provides up to
1,400 pounds of withdrawal resistance. Two lags would easily handle
the lateral resistance requirement. And in the case of attaching to
foundations, all manufacturers make adhesive anchors tested to well
over the 1,500-pound load specified in the IRC for lateral
As always, though, consult your local building official.
Contributing editor Glenn Mathewson is a
building inspector in Westminster, Colo., and the author of Deck
Construction Based on the 2009 IRC, published by the International