[MF231]

when you cantilever floor joists it changes the span rating. Geometry thing. If you cantilever 4 foot you have to have 16 foot of joist before for loading purposes. Which on a deck might be less.
And as stated a simple drawing would help.

Agree with IronP. I’ve always been told by engineers in the past that the rule of thumb on cantilever is 2/3 in for every 1/3 cantilevered.

 

[MF231]

OP, i think the advice from others above is solid. Couple of questions/comments:

• how high above grade is the top of finished deck?
• is frost line a consideration? Assume you will have posts that the beams attach to. Make sure you have proper slope (especially if you have a basement.
• are you attaching ledger to your house or is the deck freestanding?
• make sure that your hangers/bolts/hardware are at least at least ZMax (is using Simpson).

Today, I started tearing off the old deck at my post that the original owner build. I know to be weary, but not this weary:

hangars used were not meant for Contact with PT lumber, not should you use drywall screws.

note the beam that beam that is supposed to support the joists. A few had some small wedges but most were not supported.

Check out the 2x4 ledger. I haven’t started pulling that yet. It’s a wonder that this had not collapsed before.

 

[MF231]

I definitely agree that pushing the tables to their maximum is a bad idea because all it takes is one piece of wood that didn't grow just right to fail. My concern and lack of understanding came from the Lowes deck designer that removed a support beam if I had a little over 1' cantilever. Which didn't feel right for the length of the joist used.



I'm actually debating just installing a steel structure due to the risk of forest fires in my area of the PNW. I'm going to call a supplier though as I'm worried that a fire will compromise the steel structure such that it will have to be ripped out and replaced.

Even so the wallet is taking a hit because we want to go with composite and so far we've only liked the pricier stuff.



I should give some background before I answer your questions. The first is that I'm actually replacing my existing deck which consists of an "original" and an "addition" to make what I figure is about a 700sqft deck. The original deck was made with PT wood and decked with cedar. As far as I can tell the person who built that deck did everything correctly for the time I suspect the deck was built. If I only had to deal with the original deck I'd basically rip up the decking, measure the structural, and rebuild it exactly as it was before. I cannot do that unfortunately due to the addition.

Whomever built the addition didn't even follow the span tables I posted above or any span table I'm aware of. When you walk on that portions of the deck it bounces and, frankly, I'm surprised it hasn't collapsed. To extend the deck they basically cut the fascia off one of the rim joists then attached the new, undersized joists to that rim joist. There's also some sort of cinder block structure that they attached boards to to use as structure. My bet with my wife is that it's an old BBQ. There are literally cinder blocks under a couple of the joists to "hold them up" which only work when the deck is wet and sagging low enough to rest on the block.

Unfortunately, the shoddy addition appears to be destroying the original deck because the original deck is failing in areas where it meets the addition.

To answer your questions though:

• The highest point I've measured on the existing deck is 28". I expect to stay under 30" everywhere though. In my area as long as it's 30" or less above grade I don't need a permit to build.
• The frost line is an issue but not much of one where I am in Western Washington. I'd probably dig a footing to 18" as I know that's the required depth for burying plumbing and electrical. The county deck tip sheet doesn't even mention the frost line though. The existing deck just uses deck piers.
• I'll be attaching to a new ledger which is how the original deck was attached. It's just that the existing ledger isn't up to code so I'll need to take it off to see how bad the water penetration has been. Hopefully it's not too bad and all I need to do is replace the ledger with an up to code one.
• Definitely. Both the original and addition to my deck were built using what appear to be the correct connectors. I'm going to be sure to do the same.

Yeah, that's what scares me about building this deck myself. Realistically this deck only has to last a decade though as by that point I will have enough saved up to do a big remodel to add a barn-dominium, upgraded kitchen, and have the roof extended over the deck. At that time the deck will probably need to be ripped up to dig new footings anyways so I'll make sure to have it done such that my great-grandchildren could play on it.

JLC has some good articles (old & new) regarding decks.

https://www.jlconline.com/how-to/exteriors/decks

 

[MF231]

Have not see a diagonal like that before and have built a lot of places seaward of the Coastal Construction Control Line but have not done any structures with decks in major seismic zone areas. I would say it’s a software bug.
Suggest calling Simpson tech support. Or emailing a screenshot.