Now that we’ve explored ledger attachments, let’s look at lateral load requirements, and not on handrail but on the ledger and joist diaphragm.
According to the 2009 code, decks that were supported by attachment to an exterior wall were required to be “positively anchored to the primary structure and designed for both vertical and lateral loads as applicable” [R502.2.2]. The only guidance given for the lateral load requirement was a “permitted” detail using 1500# lateral tension ties in at least two locations [R502.2.3].
A Note from the Publisher:
This article was originally written by Scott Wells, and we submitted it to Glenn Mathewson for his thoughts and feedback. For those of you who don’t know Glenn, he is a long-time tradesman, contractor, consultant and building inspector with significant experience in the field of code development and education. We decided to publish both Scott’s original article as well as Glenn’s responses as a two-part series—the first segment consisted of an exchange about ledger attachments. This final article pertains to lateral load requirements.
The code didn’t allow for any exemptions. The size of the deck did not matter. The deck’s proximity to the ground did not matter. Two tension ties per deck—period. And what did “permitted” mean? Well, in some parts of the country, it meant ‘required.’
So a lot of us carpenters—and you know who you are—climbed under crawlspaces with a socket wrench, impact driver, a big drill bit, some Simpson DTT2s, a good flashlight, maybe a crawl suit, and hopefully a dust mask. We belly-crawled under duct work, hopefully avoided any plumbing conflicts and hanging electrical, we removed insulation in a couple joist cavities (if there was any insulation), and then we got to work. It wasn’t fun, but it was tolerable, compared to installing a deck to the second story of a home, where we had the pleasure of removing (and patching) drywall so we could install DTT2s in the floor diaphragm. Youch!!
In many jurisdictions, building inspectors cover a wide breadth of projects in their workweek, stopping at commercial big boxes, strip mall tenant spaces, and multi-family apartment buildings before getting to the pier inspection for a new deck. Combination inspectors are also common, where plumbing and mechanical codes are added to the job expectation. The codes that cover a single day in an inspector’s life will take an entire shelf, and adding to that are common manufacturer requirements and referenced standards—you’re looking at not just a bookshelf, but a whole library. When a jurisdiction is about to adopt a new code, inspectors start studying. There’s not much consistency in where they start, but it likely isn’t with residential backyard decks. Even today, in 2015, many inspectors are only now discovering the code provisions introduced in 2009. When they do, they are just as confused by the “permitted” lateral load anchor provisions as the builders are.
The phrase “shall be permitted” has been used in model codes for decades, but always as a clarifier to what would otherwise be assumed prohibited, and it’s often accompanied with phrases like “except that… in lieu of… reduced by…,” or in an exception provision. There is no need to “permit” the use of an above-code piece of hardware. You can install hangers and brackets where they aren’t required. However, though it doesn’t excuse the poor use of “shall be permitted,” there is some sense to why the phrase was used.
The lateral load connection detail in the code came too early, putting the cart before the horse. Since it’s a structural connection for an unknown load, it cannot legitimately be required (only permitted). There is no argument to this fact. There is no recognized design lateral live load in any code or standard. The American Society of Civil Engineers’ Minimum Design Loads for Buildings and Other Structures, Standard ASCE 7 contains no mention of lateral live loads that would apply to decks. For gravity loads (vertical), a deck is designed to a specific load, and 40 psf is the minimum allowed by code. With a target structural limit of 40 psf, the code can confidently provide a maximum joist span based on the material selected. For lateral loads, the code merely tells you they exist and they must be considered in the design—basically identifying a target you have to hit, but can’t see. The new lateral load anchor is meant to address this by being a gigantic target…1,500 lbs. in two locations. For reference, the curb weight of a Smart car is just over 1,600 lbs. What’s sufficient for the worst case becomes completely excessive for most cases. It’s like having a single speed limit for both an interstate highway and a school zone because you haven’t established which you’re on, and thus everyone is expected to drive 25 mph. The lateral load provisions introduced in 2009 are one-of-a-kind for a number of reasons…and though good intentioned, none of them are good.
And it gets even worse! Here’s another method that wasn’t listed in the Oregon Residential Specialty Code, but is included as a prescriptive detail in the 2012 DCA-6. If the floor joists of the house are parallel with the new ledger—perpendicular to the new deck joists, the tension hardware must be installed six feet from the rim joist, with full depth blocking between each joist! And if the new deck is on the second story of the home and the lower floor has a finished ceiling…well, you get the picture. Yikes!
If you thought installing the tension hardware was intrusive, take a look at the prescribed subfloor nailing schedule for these details! For deck joists that are in-line with floor joists, the subfloor must be nailed off to the interior floor joists 6 in. on center. And if the deck joists are perpendicular to the home’s floor joists, you have to nail off the subfloor 4 in. on center. Either way, unless the whole job is new construction, it’s a guarantee you’ll have to remove floor coverings. And what if there’s a wall plate in that location? Did anyone think of that? This is what I mean by unreasonable codes.
In an attempt to make the perpendicular requirement a little more bearable, Simpson Strong-Tie came up with a detail that only requires the tension devices to be installed at two joist bays inside the house (instead of six feet), and uses A35 clips, so the floor sheathing fastening could meet code without having to remove finished flooring or walls in order to drive fasteners on 4-in. centers. But in my opinion, that’s still not an acceptable alternative.
I recently read an article in Professional Deck Builder Magazine that referred to a lateral load test performed at Washington State University in Pullman, Washington. I recommend that anyone interested in this sort of thing read the article. Glenn has also produced a great video explaining the history of the code requirement and the University’s test results:
The engineering department performed several tests, and here’s a quick summary of the one that I find the most interesting. The faculty and students built two 12 ft. x 12 ft. decks and attached them to two small sections of floor framing that represented the home’s rim band/sheathing/plate assembly, just like we’ve all built. The two decks were both equipped with 2-in. x 10-in. pressure treated ledgers and joists, Simpson LUS210 joist hangers, 1/2-in. lag bolts connecting the PT ledger to the sheathing of the floor mockup, and treated decking. The one difference in the two decks was that one deck had two code “permitted” tension devices installed, and the other deck didn’t.
The testers then rigged up a heavy duty come-along to the center of the opposite end joist and began to apply a pulling tension to the deck system parallel to the ledger. Both decks faired quite well enduring 7,000 pounds of tension. In both cases, the joists started to crack, split, and fail before the hangers and lag bolts ever failed. The largest gap observed on the tension side of the ledger was an 1/8 in.! I’m not saying that it’s impossible, but it’s hard to imagine a residential deck ever experiencing this kind of lateral load. This test shows us that the tension ties installed on the one deck were entirely unnecessary. The wood framing failed too quickly; the tension devices didn’t even matter.
One carpenter, Jim Finley, finally had enough of it. He wrote an article in Professional Deck Builder Magazine titled “Lateral Bracing Alternatives“—a reminder to us all that we can get our own engineering for deck ledger connections. And he’s got it right. Instead of dealing with all of the misinformation and problematic installations of tension ties, Jim maintains control and predictability on his deck projects by having his own engineering done for ledger attachments. Jim and his engineer have developed a few different steel connectors that meet or exceed the 3,000-lb. requirement, which means Jim doesn’t have to guess how to handle prescriptive tension tie requirements on each individual project. And, Jim can install his “tension ties” on the outside of the building without cutting open the ceiling or the floor.
In fact, the 2015 IRC provides a new detail allowing four 750# lateral load devices, instead of two 1500# connectors—an alternative that’s pretty close to Finley’s idea.
Simpson now manufacturers a new piece of hardware called the DTT1Z that takes advantage of the new 2015 detail. It can help solve most lateral load problems without any of the real honest-to-goodness headaches. The DTT1Z can be installed in a bunch of different ways—into the studs, the plate, or the foundation. There are also several approved blocking methods so that the hardware can be aligned and attached to these different structural elements, which means there shouldn’t be any reason to open a drywalled ceiling or crawl under a home in most situations. Well duh! Jeepers! Shucks! Imagine THAT!
If you want to learn more about the DTT1, check out Simpson’s Technical Bulletin: Installation Options for Deck Lateral Load Connections.
There was a lot of discussion about decks at the 2015 IRC development hearings and it yielded many much needed code provisions, such as joist and beam spans and cantilevers, post sizing, and connection details. The Washington Association of Building Officials (WABO) recognized that the 2009 lateral load detail was infeasible and developed the idea for four 750-lb. devices attached from the outside and submitted that as a code proposal. Most deck interests worked for the approval of the WABO proposal to at least ease the suffering of the intrusive threaded rod connection after a proposal to remove all the lateral load anchor provisions was disapproved at the hearings. Too often inspectors are demonized for the codes they are charged to enforce, and in reality, these same inspectors are often the ones at the front lines fighting for sensibility.
While this second lateral load connection detail is easier to install than the first, it should not be overlooked that a legitimate load target has yet to be identified, nor has it been proven that the lag screws or through bolts required to run the length of the ledger are not already sufficient for lateral loads. The two 1,500-lb. load targets were not derived from science or testing. I caution the decking industry in accepting this alternative too gleefully as it is still far from proven necessary. Additional comfort in the unjust does not make it just. It does however ease some pain until more science is revealed in deck engineering.
Currently, Washington State University is back at it again and continuing their study of deck lateral loads, yet it will be very slow due to minimal funding. There is knowledge to be gained and truth to be found in the future; we just have to be patient and supportive. Code development happens long before the publishing date. Any proposed changes to the 2015 IRC, for the development of the 2018 IRC, are due January 11 of next year. This means we have less the two months left to incorporate our current knowledge and affect any change. The 2018 IRC will be in effect until 2021—six years from now. I haven’t heard of, nor do I expect, anything earth shattering related to the lateral load provisions or the impossible ledger fastener edge distance requirements. Unfortunately the industry may have to be very patient for resolve on these issues.
I know building departments and inspectors are just doing their job when they uphold the code. They don’t have much choice. We can’t blame our inspectors for unnecessary and costly code requirements. It’s the code makers that need to clean up their act and provide us with reasonable requirements. After all, this is a business, not a hobby.
I hear the term “code makers” or “code writers” used throughout the construction industry, and often feel it’s misunderstood. While it’s easy to point the finger to “code makers,” that’s not really how it works. The only prerequisite required to be a code maker is to write it up, show up, and talk it up. Code modification proposals can be submitted by anyone—anyone can attend the hearings, and anyone can testify for or against any proposal. Code professionals (governmental members of ICC) make the final vote on code proposals, but that’s often only through the knowledge presented to them at the hearings. A good salesman speaking about a subject that the average inspector has little knowledgeable of will have a pretty good chance of “writing the code.” Herein lies a bit of the problem and the likely reason why the IRC has nearly doubled in page count since its first edition. Only those with the time and resources (both of which generally require money) are able to have a strong voice in code development. Therefore, those that stand to benefit financially from codes are the ones most willing to invest the time and resources necessary to develop them. Code is generally developed by an industry with a financial benefit, or non-profit industry associations with sufficient membership dollars to defend or enhance industry code, or from state ICC chapters with sufficient funding to send government members to attend and vote.
As contractors, the most effective way to contribute to the codes governing your industry is to keep working hard at what you’re good at and financially support the leading non-profit association to represent you and your industry in the code arena. Through member support, the North American Deck and Railing Association was able to make a major impact in representing the common builder during the 2015 IRC hearings, and it shows in the quality of code that was approved.