Thread: decking pier to post connections

hello all,
i am not a home inspector, but i find this website to be one of the most informational when it comes to building information. I hope no one minds that i am using this post to get information almost impossible to find on other sites.

I am in the process of building a small walk out deck (10 foot joist spans, 16 foot beam/ledger lengths)

the deck will be very low to the ground, with a ledger lagged to the home's first floor sill box, approxiametly 1.5 feet above the ground. on the other side of the deck is a uphill grade.

I am pouring 8' sonitube cement/concrete footings to support the twin 2X10 carrying beam (opposite the side of the home attached ledger).

in standard fashion, the footings will support 4X4 posts attached to the carrying beams

My question is the post to pier attachment. Some say it's better not to attach the posts to the cement. Should the piers sink over time, it would be easier to re -level the deck without pier to post attachment (simply jack the sagging end of the deck and shim the post.

since the deck will be very low and protected by an uphill on one side, and the house on the other, the uplift threat is basically non existent. lateral movement should not be an issue since the deck ledger is lagged to the house.

My brother in law built his own house with a large porch supported without pier to post attachments, he had a pier sink and easily corrected it using the jaclk and shim method.

i was ready to install j bolts in the cement until i spoke with him...so now i ask all of you, which is correct?

i appreciate your thoughts

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Hi David. First you are assuming the pier will sink. I personally have seen very little of that here in New England. Make sure you go down at least 4 feet for frost protection.
The Simpson deck Attachment guide has Post base/Column base with standoffs . Neither one requires the post to be in the concrete just the attachment itself. Looks to have some vertical attachment leeway if Pier does settle a bit. Then you could do your shim idea. I would dry pack grout and not wood shims if needed.
Build a Strong, Safe Deck

Originally Posted by David Camilleri

I am pouring 8' sonitube cement/concrete footings to support the twin 2X10 carrying beam (opposite the side of the home attached ledger).

in standard fashion, the footings will support 4X4 posts attached to the carrying beams

My question is the post to pier attachment. Some say it's better not to attach the posts to the cement. Should the piers sink over time,

If the piers (the footings/pilings, depending on your perspective) sink, then they were insufficient to start with.

That said, let's continue ...

it would be easier to re -level the deck without pier to post attachment (simply jack the sagging end of the deck and shim the post.

Why would it be easier? Embed 'J' bolt anchors into the concrete, drill a hole up into the bottom of the 4x4 post to allow the post to fit over the end of the 'J' bolt, then leave the full length of the 'J' bolt protruding up out of the concrete. When setting the deck, install two nuts, washer, fender washer, post bottom anchor, fender washer, two more nuts, the post, then attached the post anchor to the post (leaving at least 1/2" or more between the bottom of the post and the top nut).

Should you ever need to level the deck you simply loosen the top jamb nut and run it up the 1/2" or more you left space for, then run the second nut up, then run the third nut up (the top nut under the post anchor bottom) which raises the post, repeat until deck is level, then tighten the second nut down to the top of the post anchor, then run the bottom jamb nut up, then run the top jamb nut down.

You can do that as far as the 'J' bolt is long.

My brother in law built his own house with a large porch supported without pier to post attachments, he had a pier sink and easily corrected it using the jaclk and shim method.

He has no connection holding the deck to the piers? He is just using gravity to hold the deck down and into place?

I suspect he does not grasp the 'gravity' of the situation and need for anchors.

Unless someone can convince me otherwise, that's that way I would do it if I was concerned that the piers might sink.

But the real solution is to make larger and deeper piers, so they do not sink. Larger (as in larger diameter) piers will have greater end bearing capacity on the soil on their bottom end, however, most pilings (you did say they were 8 feet long, so I would call that a piling instead of a pier) get their support from surface friction with the earth.

Let's say that the soil will support a load of only 1500 pounds per sq ft, take a piling which has a diameter of 8 inches, that's 50 sq inches end bearing, which is 1500 / 144 x 50 = 520 pounds of bearing support.

Now, let's take skin friction of the piling, let's say the soil has a skin friction support of 300 pounds per sq ft, take that same 8 inch diameter piling, which has a circumference of 25", with an embedded length of 78" (96" piling with 18" above grade) for a surface area of 1950 sq inches, which means 300 / 144 x 1950 = 4062 pounds skin friction support. Total bearing support = 520 + 4062 = 4582 lbs.

The end bearing support (520 lbs) is very limited when compared to the skin friction support (4,062 lbs). Make that piling a 12" diameter piling and the end bearing goes up to 113 sq inches or 1,175 pounds support bearing ... BUT ... the skin friction goes up too, because the circumference is now 37.7" x 78" = 2940 sq inches of skin area for 6,124 pounds skin friction support. Total bearing support = 1175 + 6124 = 7299 lbs.

Let's make the piling longer instead of larger, so we go back to the 8" piling. Same end bearing support = 520 pounds; 8 inch diameter piling, which has a circumference of 25", with an embedded length of 126" (12 foot piling = 144" piling with 18" above grade) for a surface area of 3150 sq inches, which means 300 / 144 x 3150 = 6562 pounds skin friction support. Total bearing support = 520 + 6562 = 7082

If you are worried about it sinking, go to a larger piling of the same length or a longer piling of the same diameter. Is it easier to dig deeper (50% deeper) or bigger around (50% larger diameter)? Makes a big difference in support for your deck.

The 8 foot long 12" diameter piling will take more concrete than the 12 foot long 8" piling.