Carpentry people: Deck questions

[Greenman]

The critical area of the ledger connection to the structure is under addressed in code IMO. Specifically with flashing, it seems to leave the execution up to individual interpretation. Nearly all code compliant deck failures that I am aware of are due to water intrusion and rot at the ledger board.

Free standing decks, like the OP is having built, are ideal because they avoid the issue almost entirely.

I believe that's been addressed. I can't site the actual code, but it's something I always have to detail quite clearly for the building department's around here. I always use a product called "Off The Wall", which is nothing more than a spacer behind the ledger. Using the spacer, flashing details become elementary.
The only other real issue I commonly see is the wrong connectors being used. I've seen more than a few new decks with standard hangers on them, they won't last more than a year or two around here.

 

[VulgarDisplay]

The article I posted about fasteners kinda addresses the hanger issue as well, you need to make sure whatever metal parts you are using received the proper galvanization to stand up to the copper content of the treated lumber.

 

[Humpy]

Here in the land of fruits and nuts, we have a plethora of standards to meet. I have plans sitting on my desk right now that site ten different codes/standards that have to be met. It's getting out of control.

Damn... You're a contractor in California? Mojo sent.

 

[Humpy]

I think the OP is in good shape with his contractor...

I do too.

 

[Greenman]

Damn... You're a contractor in California? Mojo sent.

Indeed I am, at least until I'm regulated out of business. It's getting really out of control in some areas around here. One city has gone so far as to impose standards on what windows look like. It turns out that only high end Marvin windows meet the standards. Adds a lot to the budget.

 

[Greenman]

The article I posted about fasteners kinda addresses the hanger issue as well, you need to make sure whatever metal parts you are using received the proper galvanization to stand up to the copper content of the treated lumber.

Z-Max is your friend.

 

[Gunslinger08]

Checked out the lumber today. 6x6 posts and 2x10 joists with 12" spacing.

 

[mizzou]

with composite decking, I believe you double the amount of floor joists needed vs pressure treated or cedar decking. That stuff is extremely heavy.

 

[edro]

Checked out the lumber today. 6x6 posts and 2x10 joists with 12" spacing.

BAM! We were dead on. Sounds like your contractor knows what he is doing.

 

[skimple]

As for the beam, I am not a fan of setting the beam on top of the posts and then joists on top. When I was framing for a living we always put our 2x12 beams on opposite sides of the posts and then bolted through the whole thing.

This is against code in my area. The entire weight of the deck then relies on the shear rating of the hardware. You have to either notch the post, or set on top and secure using a plate or some other means.

+1 for placing joists at 12" O.C.

 

[bonkers325]

josh,

quick napkin math indicates that 2x10 joists are more than sufficient for deck joists @ 12" o/c. enjoy your deck!

 

[skyking]

No kidding, sounds "bomb-proof" as my neighbor would say.

 

[Howard]

This is against code in my area. The entire weight of the deck then relies on the shear rating of the hardware. You have to either notch the post, or set on top and secure using a plate or some other means.

+1 for placing joists at 12" O.C.

I don't know how they came up with the code, but it seems like for 1/2" fasteners or bigger, any reasonable load on a deck would be no problem at all when fully shear-loaded.

 

[MagnusTheBrewer]

Actually, it is good enough. I've been in the industry for 35 years, and I've never seen a code compliant deck fail do to meeting code. I've never even heard of it happening.

I have seen decks built to code fail, specifically in the Mid West due to heavy snow loads. But, besides the possibility of failure, there are performance issues. Specifically, flex and washboarding when using man made decking and joists are spaced more than 12". Also, few codes I am aware of specify the type of fasteners allowable for securing decking.

 

[Howard]

I have seen decks built to code fail, specifically in the Mid West due to heavy snow loads. But, besides the possibility of failure, there are performance issues. Specifically, flex and washboarding when using man made decking and joists are spaced more than 12". Also, few codes I am aware of specify the type of fasteners allowable for securing decking.

Wow. Given that snow weighs, at worst, 62.4 lbs/cu. ft (I hate imperial), that works out to 0.8 psi vertical area load for no less than 2 feet of compacted ice/snow. Code sucks.

 

[Humpy]

I don't know how they came up with the code, but it seems like for 1/2" fasteners or bigger, any reasonable load on a deck would be no problem at all when fully shear-loaded.

It would probably not be a problem. But why rely completely on the shear strength of fasteners when the immense compressive strength of lumber can be utilized simply by notching or stacking?

Wow. Given that snow weighs, at worst, 62.4 lbs/cu. ft (I hate imperial), that works out to 0.8 psi vertical area load for no less than 2 feet of compacted ice/snow. Code sucks.

All of the deck collapses I am aware of happened during parties when the deck was packed with fat, drunk people.

 

[edro]

It would probably not be a problem. But why rely completely on the shear strength of fasteners when the immense compressive strength of lumber can be utilized simply by notching or stacking?

Right.
That method is definitely against modern practice and code.

It's not just the shear force of the hardware at play using that method though.
The fasteners create a ton of clamping force, essentially eliminating most shear on the fastener. That's the main reason that method works so well.
But again, notching AND clamping is definitely the best method.

 

[Howard]

It would probably not be a problem. But why rely completely on the shear strength of fasteners when the immense compressive strength of lumber can be utilized simply by notching or stacking?

I like it when the minimum amount of cell walls are damaged.

 

[Humpy]

Right.
That method is definitely against modern practice and code.

It's not just the shear force of the hardware at play using that method though.
The fasteners create a ton of clamping force, essentially eliminating most shear on the fastener. That's the main reason that method works so well.
But again, notching AND clamping is definitely the best method.

The clamping force is not predictable long term as the wood moves seasonally and shrinks. I think of fasteners as a way to hold things in position so the structural material can do its job. I'm no engineer though, just a carpenter.

 

[Greenman]

I have seen decks built to code fail, specifically in the Mid West due to heavy snow loads. But, besides the possibility of failure, there are performance issues. Specifically, flex and washboarding when using man made decking and joists are spaced more than 12". Also, few codes I am aware of specify the type of fasteners allowable for securing decking.

I've never dealt with snow load, but I would assume it's figured as an added dead load on the deck. It looks like 2' of compacted snow would reach the design limit we use around here. I assume local code would account for that load.

Joist spacing is determined by several factors, but the requirements of whatever the deck surface is have to be met. I've used a couple different man made materials that spec 16" centers. I've never encountered washboarding on anything but a Trex deck. I don't like Trex and don't use it, so I never investigated the problem.

Around here, fasteners going into PT material have to be ICQ rated, stainless steel, or hot dip galv.

 

[Kreon]

Wow. Given that snow weighs, at worst, 62.4 lbs/cu. ft (I hate imperial), that works out to 0.8 psi vertical area load for no less than 2 feet of compacted ice/snow. Code sucks.

Remember that building code usually states in psf. So its 124.8 psf for 2 ft of snow. A 100 sf deck (only 10x10) incurs an additional 1248 lb. That is not an insignificant load.

Massachusetts Building Code states the snow load ranges between 25 and 40 psf, depending where in the state the building is. On decks (or flat, stepped roofs), you also have to take drifting into account. So assuming only 25 psf on a 10x10 deck, that's an additional 250 lb (assuming no drifting).

So while not huge on a small deck, on larger decks it can be an issue. It can even be an issue in large buildings (pro tip: if you're building something in New England, make sure the Florida firm you hire to do the structural design knows about the snow issue. True story).

 

[Kreon]

I've never dealt with snow load, but I would assume it's figured as an added dead load on the deck. It looks like 2' of compacted snow would reach the design limit we use around here. I assume local code would account for that load.

Sometimes a dead load, sometimes a live load. Depends on the code. Most places call it a dead load (IBC does iirc). There are some places that consider it a temporary load (an thus live). Mostly in southern states, where snow doesn't really come into play.

 

[Greenman]

Sounds like a pain in the ass. I'll stick with lateral loads where the only question is, how much does an earthquake shake?

 

[Kreon]

Earthquake dynamics make my head spin. Really the only structural thing that I struggled with. Fortunately we don't get to many scary ones in Boston (though there are dozens of ancient fault lines criss-crossing the city. Will be very bad if we get a big one).

 

[bonkers325]

Remember that building code usually states in psf. So its 124.8 psf for 2 ft of snow. A 100 sf deck (only 10x10) incurs an additional 1248 lb. That is not an insignificant load.

Massachusetts Building Code states the snow load ranges between 25 and 40 psf, depending where in the state the building is. On decks (or flat, stepped roofs), you also have to take drifting into account. So assuming only 25 psf on a 10x10 deck, that's an additional 250 lb (assuming no drifting).

So while not huge on a small deck, on larger decks it can be an issue. It can even be an issue in large buildings (pro tip: if you're building something in New England, make sure the Florida firm you hire to do the structural design knows about the snow issue. True story).

stop spreading your misinformation

2ft of snow is approximately 40psf. probably 80psf maximum where deck meets side of house, and that's a rather conservative estimate.