deck ledger connection

huangyhg

deck ledger connection
i have a deck ledger question.  the irc supplement (r502.2.2.1.1) has the following:
"placement of lag screws or bolts in deck ledgers. the lag screws or bolts shall be placed 2 inches in from the bottom or top of the deck ledgers and between 2 and 5 inches in from the ends. the lag screws or bolts shall be staggered from the top to the bottom along the horizontal run of the deck ledger."
in the plans for a deck design i did, i specified 1/2" lag screws at 16" o.c. staggered, with a 2" edge spacing.  however, the contractor installed (2) 1/2" lag screws every 16" o.c.  there is 2" between the edge and the top lag screw, and 1-1/2" between the edge and the bottom lag screw (see attached photo).  
i think this connection detail meets the spacing requirements in the nds (unless i'm not interpreting the requirements correctly).  table 11.5.1a (edge distance requirements) for loading perpendicular to the grain, lists a minimum edge distance of 4d for the loaded edge (2" for a 1/2" lag screw) and 1.5d for the unloaded edge (3/4" for a 1/2" lag screw).  i also ran a calc for the loading on the screws and i can show them good.
am i missing something?  if my calcs are ok and the contractor provides them to the building inspector, will he still have a problem with the connection since it is not per the irc?
reading the first paragraph, you need one at the top, then one at the bottom, and the spacing between the tops would be 32", and the bottom 32" but 16" between top and bottom.
thats the way i understand the paragraph to read.
i just think you have too many lags. better have them take them out
the reason for staggering the lag bolts is to reduce the potential for an interconnecting crack between the holes.  depending on the width of your ledger, this can be an issue.
the crack can develop from drying shrinkage or creep, though ledgers are not usually heavily loaded so creep would likely be less of an issue.
the edge distance given by the code is the minimum in the absence of engineering that can show otherwise.  you have apparently done that and the building official can review and approved based on submitted supplementary engineering information, particularly when you can back it up with nds compliance.
if the question arises certainly calcs to back it up would satisfy the building department.
i always like using simpson sds 1/4" lags.  great shear value, less impact on both the ledger and studs, no pre-drilling required, more likely to connect to the stud in the center with adequate edge distance.
  
mdj
thanks everyone for your input.  i was doing my calcs and i'm having trouble showing it good.  so i thought i would check my calculation procedure by verifying the spacing requirements in irc table r502.2.2.1.  i must be doing something wrong, because i cannot show good what they have in the table.
say for example i have a southern pine ledger and a spruce-pine-fir band joist (as described in the table heading).  also the deck ll = 40 psf and the dl = 10 psf.  the joist span is 10', so the loading per foot along the ledger would be:
w = (10 ft/2) * (10 psf + 40 psf) = 250 plf
for 1/2" lag screws, the recommended spacing in the irc table is 18" o.c.
if the screws are 18" o.c., that would mean the load each screw carries would be:
p = 250 plf * (18"/12 in/ft) = 375 lb
for the allowable load per lag screw (prior to applying adjustment factors), i'm calculating z = 180 lb (considerably less than the required value of 375 lb).
i have attached a copy of the irc table along with a screenshot of my spreadsheet calcs.  i have checked the formulas in the spreadsheet by running some examples from breyer (design of wood structures, 6th edition) - the results match, so i don't think i have any errors in the spreadsheet equations.
does anyone see an error in my calculation procedure (either for the loading on the screws or the allowable screw load)?
thanks for your help!

the attachment for my last post didn't get attached - hopefully this will work.
residential or commercial construction?
many local codes over-rule the national codes because of experience and do not allow lag bolts and permit only though bolts if you are attaching to a rim joist or similar. - that plus the detailing, construction moisture/mold problems are the reasons so many frees standing decks are built. many situations do not permit access to provide trough bolting. they just set the posts 2' beyond the wall to avoid the footings and the deck is cantilevered back 2' to the structure.
you cam still make one or two selective connections (limited moisture exposure) to the existing structure to provide some lateral resistance. a deck surface with properly attached deck boards on a diagonal will also help with lateral stability. - all of this is beyond computers, and a "sit back" observation always helps.
dick
dick - lag bolts are allowed in my area.
my problem (described in my last post) is that i can't show the spacing specified in the irc table as good (i must be making a basic mistake, but i'm not sure what it is).  if someone could take a quick look at my calcs and let me know if i'm doing something incorrectly, i would really appreciate it.
don't you have 2 bolts?  i couldn't see it in your spreadsheet.  
also, diameter = .371?
i do have two lag bolts, and i wasn't able to show them good for my loading...
so i decided to run the calcs for what is shown in irc table r502.2.2.1.  for my example calculation i chose a southern pine ledger and a spruce-pine-fir band joist, deck ll = 40 psf and the dl = 10 psf.  the joist span is 10'. there would be one lag bolt every 18" o.c.
regarding the diameter - a 1/2" lag bolt has a reduced body diameter of 0.371".  i think that would be the diameter i would use in the calcs (at least that is what was done in an example i looked at from breyer).