Replacing deck support posts

I started what was to be a fairly small project that has turned ugly due to all the support posts under my back porch deck either being already rotted through or in various stages of rot. They were rough cedar. Half were concreted into heavy black clay soil(1 foot or so on top of the parent material soil which is limestones on top of limestone slabs with minimal soil), and half were just dug in.
The damage was done, I believe, by very poor drainage due to the builder leaving the soil in piles in a way that ran the runoff water right into the posts.
I cannot get post hole diggers or even a standard shovel under the deck to dig new holes because it is too low and it is also roofed over.
I am thinking that I can place concrete blocks under the rim joist close to where each rotting post is, cut it out, and then place blocks for support where the old post was. The old posts are directly below the posts that support the roof over the deck.
Or I could dig a hole as deep as I can after cutting out the rotted post and pour a pier with a metal standoff bracket anchored on top and use a post above that to go up to support the rim joist.
Does anyone out there have any experience with this problem and know of any other way(s) to address it?
Thanks for any assistance.
RonT
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A large part will depend on what the frost depth is in your area. Here in Minnesota, frost footings are required to be 42" -- I wend 48" for our new deck this summer. If you simply place concrete blocks on the ground, that creates a 'floating' deck and will cause damage if parts of it are attached to your house, which it sounds like they are.
-Tim
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Sounds like you inherited bad drainage and worse construction. I agree with Mr Fischer's comment about floating decks. It sounds like you need better temporary support for both roof and deck. To give a useful suggestion, one would need a more complete description of the structure. TB
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Sure you can. Pull up the decking. You've already seen what a half-ass job ends up being. Don't repeat it. Correct the drainage problem FIRST. No job will be worth doing if the water gets back in there and rots it out again. THEN pull up the boards and put down proper holes for the posts. Check with your local code and DO IT RIGHT. If the roof you've got on this is already attached to your house then you don't want this deck heaving up/down due to winter weather or other conditions. Properly sunk posts will avoid this trouble.

That complicates things, of course, but if you make enough room you should be able to dig out a hole at that point and sink a new post to support the one above it. No sense in putting down columns elsewhere and then end up having the roof start sagging.

As deep as you can't won't matter if you're in frost area. You have to dig it to the depth code requires. Otherwise you're just asking for new problems.

Yes, that would be one idea that might work.

I've tried working around an existing deck. More often than not it ended up requiring removing existing decking material anyway. Best to just cut to the chase and do the job right.
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Correcting the drainage will be no. 1 on the list. Since I'm roofing over the new deck I will concentrate on the far ends and get them out of harm's way. The yard slopes pretty good which will help.
The frost consideration here(Austin Texas area) is minimal since we rarely get below 32. But to be safe I'm going to go down 24 inches(further if the building codes call for it) or to the parent limestone material, whichever comes first.
I'll probably try hacking away while under the deck first to see if I'm getting anywhere with the holes for the piers. Then remove decking and get more agressive if I get nowhere. With the posts needing replacing being directly under the roof support posts and the rim joist it will be difficult either way but should be doable.
RonT
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