These prescriptive codes are driving me crazy. We will never be able to prescribe the perfect magnitude for loading or whatnot and the perfect detail for every conceivable condition that someone could come up with. Someone who knows what the heck he/she is doing has to be able to make a good sound engineering judgement about something like this, and many other details and conditions, not specifically covered by the codes. We shouldn’t be leaving this kind of thinking and decision to weekend carpenters or inspectors who don’t have a handle on the engineering concepts involved, nor can we codify every possible condition. The fact is that the codes don’t cover decks very well, and in part that’s probably because they are just too difficult to put into neat little design groups, like tabulated fl. jst. spans. The majority of decks just need some good common sense (which is all too uncommon, read the damn manuf’ers. instructions and footnotes too) and some good clean detailing to be just fine. There are also hundreds of variables which can really change the picture.
How are those ledgers connected to the bldg. and through how many layers of foam insul., etc. The connectors (nails, small lags w/o washers?) look pretty small, with large spacing, and the top connectors are too close to the top edge of the ledger. I think I still see the corner trim for the vinyl siding, at the ledger intersection. The ledger should be against the bldg. osb sheathing and flashed behind and over the ledger. What I see in Keystone’s picture is something the guy heard, needed doing, but with no understanding of what, and why, and where. If needed, I would put that type of lateral tie hardware a few feet from the outer edge of the deck, where it is much more effective. DRP is right in several respects: I would continue the blocking in the two open jst. bays to the ledger; and if this is just an 8x10 or 10x10 deck in the corner, this type hardware is probably not required. The 2x10 blocking is just fine for this purpose, obviously the connection inside the bldg. must be adequately made and blocked too. And, that is tough to do without ripping up flooring so you can nail the blocking to the subfl. and so you can install the blocking, and so you can double the nailing at the sub.fl. to the rim jst. Obviously, this can be done easier on new construction when you know you will have a deck.
Here is some of my engineering logic on the picture and the comments so far:
1.) The hardware installed so close to the jst. hangers is a waste. There is most likely sufficient lateral resistance on that end of the jsts. through the jst. hangers. Jst. hangers have a good gravity and lateral load cap’y., but aren’t worth a darn in pull-off (from the ledger) along the length of the jst. For the hardware to be tightened so it works, it tends to flex the two jsts. laterally, and the only thing which prevents this is the two nails/screws in each deck board in that immediate area. Thus, the want for blocking back to the ledger, to bring more deck board/jst. connections into play and to allow me to tighten the threaded rod. The deck board over the blocking should have a few more screws down into the blocking also.
2.) The idea that the deck is adequately supported in the exterior house corner goes something like this... it has two properly affixed ledgers and properly attached jst. hangers, etc. Then applied lateral loads (particularly wind) in the N-S or E-W direction are taken into interior fl. framing in compression and really can’t be applied to cause much tension at the deck jst. hangers. But, with EQ or crazy people loadings, out near handrails, you can get this tension loading, and that’s why I would like the hardware within a few feet of the outer edge of the deck in each direction. There are many details and conditions which might complicate this need for lateral tie-back, that’s why the need for some experienced judgement, not a simple prescription.
3.) On a simple 10x14 deck which extends out 10' from the ledger/bldg. there isn’t real much chance of lateral loading problems. The worst case is a large lateral loading out near the handrail, and I do worry about a bunch of drunk football linemen all swingin to the same music out there. If the deck is off an upper level bedroom you probably wouldn’t be having the same kind of party on the deck. If you have screen walls you can pick up larger wind load components. Otherwise, you have the face area of the rim jsts. and handrail system exposed to the wind. I am usually very conservative on this issue and consider the face area of a bunch of regular jsts. too, since the wind will curl up under the deck too. And, you can have wind uplift of the deck. Then, I consider the deck system as a semi-rigid diaphragm, it will rack quite a bit, vs. an osb diaphragm. Thus, one corner of the deck is in compression into the bldg. and the other is tending to pull away from the bldg. at the ledger. Thus, the possible need for tie-back hardware. I like to put the hardware on the 1st, 2nd or 3rd interior jsts., or about 3 jst. bays into the deck system so as to bring adjacent jsts. into play through the deck boards. I want to maximize the lever arm for this tension reaction from the corner in compression, but if I put the hardware on the rim jst. or even the 1st interior jst. I don’t get very good load distribution to adjacent jsts. Again, obviously, a proper connection has to be made inside the bldg. And, we don’t always know which deck corner will be in tension. EQ’s and other details complicate this discussion further. Also, if the deck is 10x20 with a 10' ledger on the bldg., then the potential lateral loads can be applied much further away from the ledger, and my resisting lever arm is much smaller in proportion to the 20' deck cantilever length. Obviously, some serious tension tie-backs near the corners becomes important. Also, the lateral loads in the N-S direction tend to be taken out near (or at) the E-W edges of the deck. So, on all decks you should consider what to do in the way of bracing the outer (or all) posts so that they can take these lateral loads to the foundation.
