[sathson]

Apologies in advance this post got a little long!


Hello, just discovering these forums while researching a project and they seem like a great resource. The project I'm researching is a deck build/rebuild on a house we bought last year. The current deck is 30+ years old and is starting to get pretty rough, I'm concerned about building it back exactly the way it is now though because the spacing of the joists seems pretty far apart and based on the charts I've looked at the beam may not be quite thick enough. The deck is essentially on the 2nd story of the house and extends out over the walkout basement. The entire frame, joists, posts, and beams, are made of rough cut 4x6 cedar. The joists are 4' on center and the beam span is about 6' except on the part over the walkout where there are two sections which are 16'. Here's a drawing of what I currently have, the blue lines are the current joists 4' on center, its also worth mentioning the way these posts attach to the house is they actually run through the rim joist on the house and rest on top of the concrete basement walls.

 

[Nealtw]

How long are the joists on the 27 ft side
There is nothing there you would build today.
It does sound like you have a step down from the door and that is required in most places now.

 

[sathson]

The joists are 12' on the 27' side. There is a little bit of a step down but not much, maybe an inch or so.

 

[Nealtw]

The joists are 12' on the 27' side. There is a little bit of a step down but not much, maybe an inch or so.

In most places now you want 6" from the subfloor of the house to the deck framing. Do you know what the floor joists in the house are?

This is a fairly big deck, big job.

What are the posts now, are they in concrete or brackets?

 

[SPS-1]

See link below for Prescriptive Deck Code. Your local jurisdiction may have additional requirements, but this should be a pretty good starting point.

https://awc.org/pdf/codes-standards/publications/dca/AWC-DCA62015-DeckGuide-1804.pdf

 

[sathson]

@Nealtw I figured we would want a bigger stepdown but I also was hoping to replace the joists that run through the rim joist on the house and not leave them open since those are pretty big openings. I know I could cover and seal them but it seems like having that post tight in the opening makes up for some of the strength lost by having the hole cut out.


It is a big job for sure, we had originally planned to hire it out but unfortunately that is just not a possibility right now.


The posts are in concrete all the way around right now.

 

[sathson]

@SPS-1 Thanks for that link I will keep it handy. My biggest concern is the current joists being spaced every 48" and by all counts it doesn't seem like they are big enough even if I add new ones in between making them 24" on center.


I think more than anything what I'm looking for is whether going back with 4x6 joists and making them 24" on center is enough or if the whole thing needs to be designed from scratch. Amazingly the deck as it sits feels extremely solid, no bouncing or shaking when walking or even jumping on it.

 

[Nealtw]

@Nealtw I figured we would want a bigger stepdown but I also was hoping to replace the joists that run through the rim joist on the house and not leave them open since those are pretty big openings. I know I could cover and seal them but it seems like having that post tight in the opening makes up for some of the strength lost by having the hole cut out.


It is a big job for sure, we had originally planned to hire it out but unfortunately that is just not a possibility right now.


The posts are in concrete all the way around right now.

I imagine the post need replacing, will they be in the right place for new ones to use the same concrete bases?
What is the foundation, concrete, concrete block.

 

[sathson]

I imagine the post need replacing, will they be in the right place for new ones to use the same concrete bases?
What is the foundation, concrete, concrete block.

The posts definitely need replaced, some of the concrete bases can be reused but not all of them.

The foundation is concrete.

 

[Nealtw]

The posts definitely need replaced, some of the concrete bases can be reused but not all of them.

The foundation is concrete.

Should be able to bolt the ledger to the foundation and pick a height you like

How many posts do you have I am roughly counting 10 or 12?

 

[sathson]

Should be able to bolt the ledger to the foundation and pick a height you like

How many posts do you have I am roughly counting 10 or 12?

I am not there to count at the moment but I believe there are 12.

 

[HotRodx10]

I think more than anything what I'm looking for is whether going back with 4x6 joists and making them 24" on center is enough

I'm not sure of the code requirements that may be applicable, but I can tell you from my own deck that 2x6 decking on joists spaced at 24" doesn't have any noticeable flex or bounce to it; it's rock-solid. If the joists are sufficiently stiff, you aren't constrained by code requirements, and the new decking will be 2x6 or 2x8 lumber (5/4" thick decking or 2x4 lumber will considerably less stiff), then adding joists between the existing should work just fine.

Amazingly the deck as it sits feels extremely solid, no bouncing or shaking when walking or even jumping on it

If the decking is also rough lumber, it's not so surprising, since rough lumber being nearly the full nominal dimension (presumably 2") would be more than twice as stiff as "dressed" 2x lumber (1.5"). Width is also important, as weight of your foot is distributed over twice as much width on a 2x8 as a 2x4.


Also be aware that a rough 4x6 will be about 36% stronger and 48% stiffer than a dressed 4x6, assuming the wood material properties are similar, which I would suspect they're not. You'll not likely match the strength or stiffness of rough lumber from 30+ years ago with what you'll find today, even in rough lumber.