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  1. #1

    Default Deck Footing Help

    Hello,

    I am replacing my (4) 4x4 post with (4) 6x6 post because my 16x16 deck sways a lot when there are people walking around on it.

    The deck is 16'x16' square and the current deck post are 10' in height. Attached in the first posting are pictures for review.

    My question is how do I calculate the footing size I need to make in order to support the new 6x6 post? The deck is built on sandy soil on Long Island, NY.

    Also, is there any type of membrane that needs to go in between the 6x6 and the post base to prevent water seepage into the 6x6?

    Thanks,

    Pat
    Attached Files Attached Files

  2. #2
    Join Date
    Jun 2012
    Location
    Cincinnati, OH
    Posts
    173

    Default Re: Deck Footing Help

    Sand is good and the best to build on, it compacts better than any soil or rock. Have you got yourself a concrete saw? Start cutting the existing concrete out.
    Thomas Decks, LLC
    Tara

  3. #3

    Default Re: Deck Footing Help

    I plan on just breaking up the concrete with a sledge hammer. I'm trying to find out what the appropriate footing size would be for this deck...

  4. #4
    Join Date
    Jul 2012
    Location
    ATLANTA MARKET
    Posts
    17

    Default Re: Deck Footing Help

    first, the sway is not a function of post size. its a result of insufficient lateral bracing. having said that, at 10' high the 4x4's are not code complient. not here in the SE anyway. even 6x6's would need to be braced at that ht. ie, "Y" braced like you have currently. when you do this replacement run the bracing up onto the face of the beam rather than attacting to under beam.

    however, this bracing has nothing to do with lateral bracing of the deck though it can serve that purpose as well and often, this is the only lateral bracing done. over time the tendency to sway works at the fastener points and pulls them apart unless bolted which is seldom the case. what it actually has to do with is keeping the posts from bowing. which of course could happen in any direction. BUT, bracing is only required in the same direction as the beam in our neck of the woods. don't make much sense but it is what it is.

    and, in our neck of the woods, pier size for decks is minimum 16x16x12" or to "firm soil". "firm" is determined by probe. depth for your's will obviously be different. call the bldg dept and ask. you can do that even if you are not planning on permitting. then the next thing to do is inspect for existing piers. you can do this since your posts are at or near the patio perimeter. you may find sufficient piers under patio at current post locations. so, rather than start cutting or banging away with rhonda (sledge hammer - help me rhonda, help, help me rhonda), start digging to inspect for size and depth of concrete at current post locations.

    if insufficient then you have a whole new ballgame. in your neck of woods pier holes will likely be your greatest challenge so seems to me wise to consider only doing as many posts/piers as are required. though its arguable that code minimums should be regarded as insufficient to guarantee performance over the long haul, in my experience beam clear spans is not one of them. what i'm saying is if the beam of your 16x16 is double 2x10's (minimum), then three 6x6 posts are sufficient for support. i've seen a lot of things over the years that call to question code requirements but beam deflection, if done according to official span charts is not one of them. any deflection is generally more a result of reverse crown than one of load. allowable joist spans is a whole 'nother can of worms though.

    not clear in your photo if beam is doubled. regardless if you take my suggestion to eliminate a post or not, in any case shoulder cut the posts so the beam has full bearing on the posts. then thru-bolt them together. and, likely easier to double the beam if it isn't already than doing 4th pier and post.

    that the 4x4's go thru the face implies it is only single or not all of second member is supported by the post. if single 2x10 i think its undersized anyway even with 4 posts under it. tributary load on that beam would be 10' if the cantilever is 2'.

    as to lateral bracing, run a diagonal (ie, 2x4, decking board, etc) under the frame from house ledger to shaker beam making sure of solid fastening at contact points with all frame members and particularly where the diagonals butt join out in the field since you will have to at least 2-piece this brace. i'd tie them together at such point by scotching a second board a couple feet long centered at the connecting point. and i'd do bracing in both directions on a deck your size and ht. iow, an "X" pattern with a secondary member at the center point that locks the bracing together.

    as to a stand-off... i never use them unless a client specifies. i've pulled hudreds of PT SYP posts from the ground over the years and very seldom ever see any deterioration to the extent of concern. these post are inground rated and can rest in direct contact with cement. what i do find more often than not is improper installation. typical scenario: they dug the hole, threw a block (like a 2x10 about a foot long) in the bottom, set the post on it, and then poured concrete around it. this is still happening today even with pier inspections along with sufficient positive attachment of post to pierm at final inspection. what i find is severe deteriation of the block while the post is fine. or, they threw in a little dry redi-mix, set the post, then poured the rest around the post. i can't tell you how many posts we've pulled up with the "pier" clinging to the post! and it ain't because they were tied together with a metal fastener!! once again, we're in an area where minimum depth is 12" so pulling posts is usually not a big deal.

    in an ap like you show where posts are at or very near the patio perimiter, here inspectors would allow us to dig under patio to sufficient size and depth to firm soil and then pour full to bottom of patio. post would need to be positively attached to patio to prevent uplift and lateral movement but not necessarly with a stand-off. approved attachment components can be as little as 1/8th the cost of stand-offs.
    Last edited by tom logan; 08-11-2012 at 06:22 PM.

  5. #5
    Join Date
    Jun 2012
    Location
    Cincinnati, OH
    Posts
    173

    Default Re: Deck Footing Help

    6 holes, 16" deep and 14" D..you can use quick set if you plan to build the same day, but not hydraulic, pour it 8" deep and encase your 6x6 in it. Hope you got a 2x10 double beam. use 5/4 4x4 decking screwed to underside of joists to remove sway notch your 6x6's and use a 2x6 treated cap to stabilize beam on 6x6. That deck won't go anywhere.
    Thomas Decks, LLC
    Tara

  6. #6
    Join Date
    Jun 2009
    Location
    metro detroit
    Posts
    213

    Default Re: Deck Footing Help

    Dig the holes 4' deep,12" diameter, put the post in the hole on top of 6" of gravel and 1 80' bag of concrete, bag fill with whatever came out of the hole compact with a spud bar, in most cases the depth of the post in the hole will make for very stable 6x6 post and than you won't have to use those attractive x braces on your post. The gravel at the bottom of the post will provide drainage, also you are in sand which drains nicely, unless of course when you dig the holes there is standing water @ the bottom of the holes.
    If there is than you most likely have water around the foundation of your house which is another problem.

  7. #7
    Join Date
    Jun 2012
    Location
    Cincinnati, OH
    Posts
    173

    Default Re: Deck Footing Help

    This is me pushing the imaginary "like" button
    Thomas Decks, LLC
    Tara

  8. #8

    Default Re: Deck Footing Help

    I am so confused with all of the choices. Right now, the top beam is a double 2x10. I plan on adding an additional 2x10 to make it a triple beam.

    I have been reading that it's not a great idea to embed the post into cement. Most articles I read recommend the use of a post base on top of the cement footing. Your thoughts?

  9. #9
    Join Date
    Aug 2007
    Location
    Colorado Springs, Colorado
    Posts
    214

    Default Re: Deck Footing Help

    Quote Originally Posted by Patrick Presti View Post
    I am so confused with all of the choices. Right now, the top beam is a double 2x10. I plan on adding an additional 2x10 to make it a triple beam.

    I have been reading that it's not a great idea to embed the post into cement. Most articles I read recommend the use of a post base on top of the cement footing. Your thoughts?
    You'll find varying opinions of this based on user location.

    I think it's WAY better to do a post in a saddle, if the post ever does fail it's really easy to jack up the deck and replace the post.
    Colorado Deck and Framing - The finest in outdoor living
    [url]www.cdfcontracting.com[/url]

  10. #10
    Join Date
    Jun 2012
    Location
    Cincinnati, OH
    Posts
    173

    Default Re: Deck Footing Help

    Patrick, Stop reading everything else but this forum....ok..dig your holes 30" and then I want you to go shopping ...get enough bags of quick set..50 lb bags..pour a bag anda half in each hole, and make sure you got at LEAST A good 10' FOOTER GOING.lIKEMr. Deck Barn said, YOUcan BACK FILL THE HOLE WITH WHAT YOU TOOK OUTfor drainage., AND IF WATER SHOWS UP IN THE HOLE..YOU'VE GOT BIGGER PROBLEMS. Anyway, also buy yourself some simpson post anchors..one for each post, and when that concrete cures, you can attach one to the top of each footer...make sure you buy the cute ones, not the ugly ones. This will keep your post from sipping up any moisture out of the concrete..should be minimal rot, and no subway for termites to travel. Posts will line up easier, and be easy to replace if you have future problems. and when you attach the anchor bolt to the metal clip, leave a gap so the wood won't rest on the concrete. if it makes you feel bettter, then add 3 or 4" of gravel to the base. I would like to think my husband trained me well, and if he pulled up on the job site and caught me doing it any different, he would write me up AND FIRE ME WHEN I got home..and that would be with no dinner because he does not Cook.
    Thomas Decks, LLC
    Tara

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