Porch joists query on ledgerboards

[Wayne Whitney]

Hello,

I am rebuilding the covered front porch deck and joist system on my raised floor wood frame house. The new joists will be installed between two sheathed walls, so I'll be using a ledger board on each side. The span is only 6', so I'll be using 2x6s 24" o.c. A couple questions on the ledgerboards:

1) Would 3 20d nails per stud 16" o.c. be sufficient to hold the ledger board to the cripple wall, or should I use lag screws? If lag screws, what size and spacing?

2) It seems like it would be simplest to set the ledger board just below the bottom of the joists and just let the joists bear on the top of the ledgerboard. Then I would toenail the joists to the ledger. The alternative would be to use joist hangers and set the ledgerboard at the same height as the joists. What are the pros and cons of each method?

Thanks, Wayne

[marson]

typically, deck ledgers are lagged. i like the fastenmaster ledgerlok (google). without consulting an engineer, you could put two every 16" and it would be more than plenty. if the deck is between two walls, the nails would probably be OK (don't have to worry about it pulling away from the house), but the fastenmasters are so slick that unless you need to give your elbow a good workout, I would use them.

if you set the joists on a ledger, you will need to block between the joists to prevent them from rolling over. also, in actual practice, getting enough bearing on a 2x ledger is tough unless you are very anal about your joist length. for that reason, when i have set joists on a ledger, i have used 4 X material, per an engineer's instructions. also, you have to prevent the deck from pulling away from the wall somehow. so with all that in mind, joist hangaring into a ledger is quicker and easier.

[BobK207]

Wayne-

I'd use 1/2" lags ......one per stud just make sure you hit them.

I'd also agree with Marson...joist hangers are probably faster & easier than toenailing & blocking.

Pro....less headroom used up with joist hangers Only an issue where impostant) , no blocking to cut / install

Con...cost of hanges in installation hardware....I use SS square drive screws :)

I think I'd but the joists closer than 24" o/c...more like 16"

24" o/c might allow the deck boards too much flex for human perception of "sturdiness"

cheers Bob

[Wayne Whitney]

Indeed, I found section 1604.8.3 of the 2006 UBC, which states:

1604.8.3 Decks. Where supported by attachment to an exterior wall, decks shall be positively anchored to the primary structure and designed for both vertial and lateral loads as applicable. Such attachment shall not be accomplished by the use of toenails or nails subject to withdrawal. . . .

Thanks for the suggestion. Their flyer nicely quotes the NDS 2001 design values for 16d, 20d and 40d nails and 1/4", 3/8", and 1/2" lags. Of course, assuming there may be a lateral load on the ledger, using nails is out by the above requirement.

Obviously this is out now, because of the prohibition on toenails, but that issue aside, if the joists are attached to the ledger at the bottom and 3/4" T&G boards at the top, isn't that sufficient to prevent rolling over?

Cheers, Wayne

[Wayne Whitney]

1/2" lags in 0.5 SG wood are good for 200 lbs in single shear according to the 2001 NDS as quoted by fastenmaster. My 6' span porch deck is subject to a design live load of 40 psf and a dead load of say 10 psf (probably less), which gives 150 plf on the ledger, or 200 pounds per 16" segment. So looks like your suggestion is right on the money!

Good point, what is the allowed span of 3/4" T&G redwood boards? Or where can I find this information?

Thanks, Wayne

[BobK207]

the connection at the deck boards & the ledger actually give very little resitance to the "parallelograming" of the entire deck / joist system

blocks placed between the joists; on top of thel edger & under the deck boards act like little "shearwalls" and prevent rolling

If you want to convince yourself nail up a small (2 joist) system (only about foot long joists) w/o blocks & see how little "roll" resitance exists...then add a block

cheers Bob

[BobK207]

3/4" deck boards are kinda thin even for 16" oc joists........a heavy persons foot fall will flex them a fair amount.

I usually do a "reasonable" test before I settle on a design (unless calcs or experience tell me things will perform)

Also T&G (IMO) is not a good choice. for deck boards

I'd use 2x material & allow side gap & end gaps such that water & debris can easily clear / dry.

cheers Bob

[Wayne Whitney]

Ahh, of course, I was only thinking of a single joist turning over, not the whole system.

Well, this is a covered front porch, it seems like individual boards with gaps would be too informal a look. The original deck was T&G, and it was nice being able to sweep/vacuum it. I am planning to pitch the porch 1/8" per foot to allow for drainage. Perhaps I should look for or make nominal 5/4 T&G deck boards for 16" o.c. joists.

Thanks for all the advice.

Cheers, Wayne

[Wayne Whitney]

So actually I lied here a little. One side is an exterior wall of the house, the other is the long side of an L-shaped wall defining the porch and supporting the porch roof. That side need not be sheathed on the porch side.

So what are the pros and cons of (a) using a ledger board with joist hangers and (b) just running the joists past the studs in the wall and securely fastening them (a la balloon framing)? This is assuming that the joist spacing and placement would allow for (b).

Cheers, Wayne