deck building question

Started by astidham, March 06, 2013, 11:04:22 PM

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astidham

Hey everybody,
I am getting ready to build a deck either 16' or 18' wide by 12' deep
my post will be a 4x4s spaced at 5'4" with a double 2x6 for the beam.
I will have a 2x6 ledger on the cabin, and 3' out will be the 1st beam, and 7' feet out from the 1st beam is the second beam, and the joist will cantilever 2'.
my plan would be to use 2x6 joist, all treated wood.
deck will be ~ 18" above ground level...
any Observations?

Thanks, Todd


"Chop your own wood and it will warm you twice"
— Henry Ford

SouthernTier

Don_P posted a link to this the other day which I found to be interesting reading:

http://awc.org/publications/DCA/DCA6/DCA6-09.pdf

Has all prescriptive deck requirements laid out nicely.

Haven't digested it all yet, but it says overhangs should be max 1/4 of the span or 1' 9" in your case.


astidham

Quote from: SouthernTier on March 07, 2013, 08:56:09 AM
Don_P posted a link to this the other day which I found to be interesting reading:

http://awc.org/publications/DCA/DCA6/DCA6-09.pdf

Has all prescriptive deck requirements laid out nicely.

Haven't digested it all yet, but it says overhangs should be max 1/4 of the span or 1' 9" in your case.
Thanks,
I will check it out
"Chop your own wood and it will warm you twice"
— Henry Ford

Don_P

That is a good pdf... and I was looking at it and your post last night, so do that to your satisfaction and I'll go back to my project. Mt Don and I were emailing last week, he noticed that it has not been updated since syp got downgraded a month or so ago. I'd use the lower grade tables for spans.

The 2x6's, I don't know their thinking but I have one idea. In Springfield IL no deck member could be less than 2x10. Basically they wanted rot time if all else failed. At 2x6 if the treatment fails in a pocket somewhere there isn't much room for reserve strength. The other side of that, I've got some 25+ year old 4'x8' decks with 2x6 framing here, they are definitely at the end of service life but that has been a good run, with CCA. I've also seen treated fail way before it should have, I can see either way.

The ledger at the house. If you tie to the house, which is a good thing for lateral stability, use a ledger, and flash the thing properly. Nailing through siding into untreated structural wood just invites water that has no good way of drying deep into your structural framing. Do that on pier and beam where individual joists cannot drop onto a wall...the girder, which was normally never considered as supporting a floor and a deck degrades from rot, if a girder fails all the joists drop, but not tomorrow. Check the girder for adding a deck then flash things properly. In this case the support is coming from the first girder row and the lateral is coming from the house. As an addition where flashing is a pain, dropping down a step or two off a small landing at the door helps with support, flash, splash and elevation to grade in many cases but does create another tripping hazard. It's always a tradeoff, it's not a bad idea even when new to get decks down away from siding. Anyway, flash behind the ledger carrying it up the wall and out underneath the ledger, turn out the bottom of the flashing below the ledger to kick water out, never invite it into anything below, always kick the water out. Install the ledger. Install another flashing that laps over the flashing on the wall, turns out over the ledger and turns down, I usually hem that edge. Go up the overlapping flashing on tha wall sheathing several inches with the tyvek or paper lapping over the flashing and continuing that wrap up the wall shingle fashion, always lap to eject water, a wall is just a steep roof, water will run down it. Then apply siding, again lapped to eject water.

I usually use 6x6's for posts out at the front rim rather than cantilevering the deck. I inset a double rim 2-1/4" deep into a notch and continue the post up as my guardrail post, creating a very strong railing. At this height you don't need any of that though

At 18" I'd think about a small landing and step down to a patio. Railroad ties, gravel and pavers?

MushCreek

One thing about deck construction puzzles me. They have recently really beefed up rules for the ledger connection, which is a good thing. But it looks like the joist hangers are typical metal brackets nailed to the ledger. What keeps the brackets from eventually pulling away from the ledger? I don't really trust nails. Considering the size and number of ledger fasteners now required, those little 1-1/2" nails don't look like much. Would the special Simpson screws be a better way to go? I suppose diagonal brackets would also reduce the tendency to pull away.
Jay

I'm not poor- I'm financially underpowered.


MountainDon

#5

A lateral load device such as Simpson DTT2Z  (above)

Use one on the joist at each ledger end. I've seen then here in a box of two brackets plus the SDS screws. About $15, plus threaded rod, washers, nuts

fig 23a  in the DCA6 guide
Just because something has been done and has not failed, doesn't mean it is good design.

astidham

Thanks everyone!
I did decide to us 2x8s for the ledger, doubled beam and joist.
the 2x8 ledger in my case will be attached to the beam under the house, which is a triple 2x12 spaced with 1/2" plywood.
the first step down will be a smaller step down on top of the deck.
"Chop your own wood and it will warm you twice"
— Henry Ford

UK4X4

I searched for that deck clamp but could not find it

it was for this deck, the connection to the cabin is just joist hangers in withdrwal

adding those brackets would make the deck so much stronger and could be fitted now, after the fact

Deck
http://countryplans.com/smf/index.php?topic=12901.0

Brackets from Don

MushCreek

Those won't work in my case. I will have a PT ledger bolted to anchor bolts which are set into the concrete wall. I suppose I could use those massive hold-down brackets intended for sill construction. They fit over a bolt, and fasten to the studs, or in this case, the joists. I would think one every 4' or so would suffice? In reality there shouldn't be that much force pulling away from the wall unless the outboard support columns failed or moved.

Alternately, I suppose I could use T-shaped straps nailed to the top and bottom of the ledger and the joists.
Jay

I'm not poor- I'm financially underpowered.


Don_P

Check the specs on joist hanger nails also, I'll bet it's calling out a 3".

astidham

Quote from: Don_P on March 09, 2013, 06:17:07 AM
Check the specs on joist hanger nails also, I'll bet it's calling out a 3".
Thanks Don... i will
"Chop your own wood and it will warm you twice"
— Henry Ford