Deck posts on concrete patio

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Old 04-13-15, 12:24 PM
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Deck posts on concrete patio

I'll start by saying this is my first post on this forum, so hello all! I searched a lot between google and this forum and aren't really sure how to do this yet. I'm relatively good at DIY construction projects and are also concerned with resell so I don't want to make some bone-headed mistake that will be a pain to fix come time to sell.

I have a house built in the 60's with a very large (newer than the house) stamped concrete patio in the back. It is no less than 6" deep and doesn't move. I did some digging next to it a couple weeks ago so I know it's more than 6" deep. I've lived here 3 winters now (Baltimore County, MD) and no shifting/heaving has occurred. I believe the patio is around 10 or 15 years old...would have to double check the paper work, but it has had a long time to settle, and there are no cracks in it.

We recently had a back door put in and the threshold is about 20" off the ground. I currently just have some stairs (stringers secured to the foundation which is brick and cinder block) going to the ground. I'd like to put a small deck off the back which will be smaller than the concrete patio itself. I'm thinking around 10' wide, 8' deep. The deck posts would all be over the concrete.

Is the concrete thick enough to support just bolting a post base with a 4x4 considering the height and size of the deck. If it's a unanimous "no" and will require busting up sections of the pad to sink in footers then I'll probably just stick with my stairs. It's not so much the effort required, it's that I'd prefer to not make giant holes in the patio in case we or future owners ever wanted to use it again.

Thanks for all your input!
 
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Old 04-13-15, 01:57 PM
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Welcome to the forums!

Just because the perimeter of the slab is 6" or more that doesn't mean it's that thick everywhere. Generally it's frowned upon to set deck posts on a slab .... but I'm a painter, the carpenter's should be along shortly.
 
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Old 04-14-15, 01:34 AM
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I'm not a carpenter, but I'll chime in anyway. For your situation, I'd be tempted to build a floating deck, not anchored to the existing stamped patio, but attached to the house to provide lateral stability (in a manner that will account for any frost heave the patio may experience). If properly constructed, and rigid enough, it should serve you well. Installing galvanized steel stand-off brackets under each deck post will prevent the ends from rotting prematurely.
 
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Old 04-14-15, 03:57 AM
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I agree with Marksr and Bridgeman45. Building a tall heavier deck is not done on slabs. Each post will need a footing dug to the frost line with post bases under each. However, it appears you are building a very low deck with possibly 10" or so posts. I would graduate to 6x6's to spread the weight per post a little more, use the post bases as Bridge suggested, but have them only attached to the posts, and not to the slab to allow for movement. Being that low, you won't have any sway to speak of, and I hate driving holes into an otherwise non leaking wall of the house, so I would make it a totally free standing deck, adding a few posts throughout the deck, bolted to your joist system.
 
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Old 04-14-15, 07:14 AM
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That's really interesting. The thought of doing a "floating" deck that isn't attached to the ground or wall seems easy enough and smarter than what I was thinking. How would you secure it down? I would think you could just bolt some blocks to the ground on each corner to keep it from shifting...not that me bumping in to a couple thousand pounds of lumber is going to make it move.... I have a spot just in front of the door to transition a deck board from the deck to the brick, flush with the door frame, so that would cover any gaps. The board would sit snug between the width of the door frame opening (slider width) and would not need to be nailed down on the brick side but would keep the deck from shifting side to side since it's half inside the frame opening if that makes any sense.

As far as resell goes, I'm curious if an inspector would have an issue with that setup. I know as far as permanent decks go, it's definitely not to code as far as I know and may raise a brow, but do inspectors usually have issues with something like that? (that anybody might know of). I'd like have lattice or some type of skirt around the deck completely concealing the deck posts but mainly for storage and to keep animals out. If the deck is free floating it would be easy enough to remove if it causes a problem with resell.

Thanks for the feedback!!
 
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Old 04-14-15, 04:03 PM
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You won't be able to move the deck, and having it floating will be the better fare, since your soil could possibly heave. Having the deck solidly fastened to a slab that you really don't know the total depth in the middle, could cause cracking problems if it should shift. At least the deck will "glide" should there be any substantial shifting. I don't think your inspectors would have a problem with your design, and they certainly won't have problem since it is not connected to the house, since it doesn't have to meet the flashing/bolting requirements.
 
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Old 04-14-15, 05:31 PM
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In your case I would not attach the deck to the house. You will be fine to sit your posts right on the concrete, but know going into it that you may have heaving issues in the future. You can mitigate this buy placing adjustable post brackets in the pad and sitting your posts on them. If something does move over time you will have an easy way to compensate for an inch or so and level it back up.

There should be no issues with a home inspection as long as you have proper lateral bracing for the posts. Since the deck is so low, the bracing is less important, but still required.
 
 

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