Deck – concrete piers or bury posts?
parttime
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Getting ready to build a deck – digging the holes. Still can’t make up my mind between using concrete piers or burying the 4×4 posts 42″ down. It will be a free standing deck about 35″ off the ground (approx 16’x37′). I’m leaning towards burying the posts since I won’t need as much concrete, no concrete tubes, post holders/base to attach post to pier. I using a 12″ post hole auger on tractor to dig the 14 holes. Any advice? Concrete piers or bury the posts? Thanks in advance for your help!
Replies
all depends what your soil/moisture conditions are I guess.
In dry areas tamping your posts in with gravel would be preferred.
I don't know about the post settling down though???
The cc serves to create surface area for bearing--same as a pier does.
My preference is to do concrete to the surface, and then use saddle connectors into the concrete. If possible, I like to attach the saddle connectors directly to the beam and then level the beam on the ground over the posts. Pour concrete around them, then pull them off and add appropriate posts. That ensures that everything is in the right location.
that's a good method.
I have successfully used wood posts. You should get .60 treated posts since your run of the mill 4x4 is only treated to .40 penetration and is not rated for burial. You can use cement in the bottom of the hole. In fact, all you really need for most decks is to drop quickcrete into the bottom of the hole, no need to add water.
In NJ, code requires us to pour concrete to grade, plus use a post anchor base for the 4x4.
Check with your local building inspector. Do which ever local codes require.
Still can't make up my mind between using concrete piers or burying the 4x4 posts 42" down.
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Sounds like you are in frost heave country.
I do restoration carpentry and I like buried posts - that's more work for us down the road. That and exposed beams with no cap flashings. If you bury the post, be sure to pour concrete around it to kill it faster. <g>
If it were my deck, I would use concrete piers because I don't want to do it over in ten years.
The ToolBear
"I am still learning." Goya
Thanks for everyone's opinions. Sounds like concrete piers are the way to go - even with the extra upfront expense of about $550 ($250 for 2 yds concrete delivered, $120 for concrete tubes, $180 for post anchors/jbolts). Any other suggestions? Thanks.
How many piers you got?
I usually get bagged concrete, rent a mixer, and fill the holes that way. I figure about 4 bags per hole, with a 12" dia. x 36" deep tube.
Most of the time I can't get a concrete truck to where I need it, and they don't want to wait around too long to be running wheel barrows back and forth.
I also mix in from bags. I use a wheelbarrow and hoe, so it's a little back breaking, but doesn't take long. 2 bags at a time, about 20 minutes per pier.
Soil is pretty stable at most of my worksites, so I cut a piece of tube only for the top 6" or so, so it looks pretty. That way I don't have to backfill the sides of the pier. --------------------------------------------------------
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I've got 14 piers. Using 12" auger. Have gone down about 42" on the holes i've dug so far, plus with two inches above ground, using an online calculator figured 4.4 - 80lb bags per hole, which would be about 63 bags total. 63 (80lb) bags is almost as expensive as having 2 yds delivered, but one advantage of bags would be having time (after pouring 3 holes) to pull a string to line up where to put in my j-bolt to hold the post holders...
Any downsides of not using the concrete tubes for the entire hole? One book I was reading was that the surrounding soil could pull the moisture out of the concrete quicker without the tubes. Also, any opinions on pouring 1 bag as footer first and then next day pour rest of the hole? Or is one monolithic pier better?
FYI.. the township BI doesn't care if I bury the posts or make piers, but suggested piers. Also, I plan on having the outside perimeter posts continue up through the deck to be used to support railings.
BIs around here want to see the tubes full length in the hole. I'm not really sure why. If we were further north, I'd say it was to minimize frost heave. But winters around here have been pretty mild, for quite a while.
And I used to mix in a wheel barrow, too. But as I get older, I'm finding that mixing concrete by hand has lost a lot of its appeal. <G>. I can rent a small mixer for about $30 for a 1/2 day. Well worth the investment.
a .60 treated post will outlast the deck.
since PT wood became available in .40 retention ( about mid-'80's )
we've always done the following
dig a 12" dia. hole to your frost depth ( 40" here )
do a one bag mix of quickcrete and dump it in the hole... smooth the top so it's good and flat
next day set your post on the footing... it's nice and flat so you can adjust it to your exact location... then plumb it... tamp gravel around it ... and start buildig your deck
the posts get more lateral resisance this way
we extend our posts thru the deck so we get more rail strength....if you need a formal rail system ..we use a sleeve post
I use a very similar detail...except for that digging to china thing.The best reward for a job well done is the opportunity to do another.
That wouildn't be allowed here- the BI would fail me.
Concrete's gotta be to grade, with a post anchor base holding the 4 x 4.
Structurally, tho, I don't see much difference between the two methods. Sinking the post in the ground probably gives more lateral support to the deck.
is that just a straight pin or a j-bolt (or sim) in the bottom of the hole?
3/8 rebar. Mostly started doing that to help me locate the posts. Easier to set the pins to a line than those big-azzed wet 6x6's.
Especially when working solo.
PeaceThe best reward for a job well done is the opportunity to do another.
He is only 35" off the ground. Assuming that is finished deck height with 2x10 joist and beams, he will on have 24" of post below the joist. I don't think lateral forces on a structure that low, and with 14 post would be significant.
Once I get over 4' of post, from grade to bottom of joist, I either bury the post or start adding cross bracing if on piers.
To keep a line of sonna tube piers straight I set a 2x4 or 2x6 single form on one of the outside edges of the form/pier line. Stake it between the holes and screw the sonna tubes to the form board at grade level. Use a simple plywood template that lips over the form to set anchor bolts. This saves a lot of string line pulling and double checking or correcting things when you have concrete setting up.
We are required to strip the sonna tubes from the piers. Unless you are setting on a formed footing, there is no way to strip a tube below grade. Just form the above grade portion of the piers.
I make that decision based on soil type, size of deck, snow loads required, climate.
None of which is in your OP
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Again thanks for everyone's input. Looks like it's a mix between burying the posts or using piers.
Piffin/everyone - More info:I live in south-central Ohio. The deck is going to be 16'x37'. No real snow loads to speak of here. The soil is considered Brookston-Crosby-Celina soil which is generally poorly draining soil. We've had above average rainfall for June, but I didn't hit standing water digging down 42". The 4x4 posts I purchased have a rating of .34 pcf. I plan on using two 2x8's for the beams (sandwiching the posts), with a beam span of no more than 7'. The deck will have 5 beams, with three posts per 16' beam (except the one end - beam will have 2 posts since making a 45 degree angle stairs) .
I mostly use 6x6 posts and that is what I was assuming.In direct bury situations, there are two things supporting the post. One is the footprint it makes on the soil under it. Your 4x4 is too small to get much purchase on most soils, so you need to do a base footer similar to what Mike Smith described to spread the load.The other source of support is soil friction on the sides of the post. Larger cross section ( 6x6 or 8x8 instead of 4x4) and longer - read deeper set) posts will gain more from friction support. This is how piers in coastal dune construction work to handle the loads.So with only 4x4, I would be using concrete piers in your soil and climate. I get precast 5' pyramid shaped piers for about $38 each.If you do go direct bury, that will save hardware and will add lateral support, but very definitly use mikes method for footing
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Everlasting deck
For as everlasting simple deck at the exit of your garden doors (patio doors are just plain ugly) yup pay your son and his buddies a nominal fee. Some good music and good humor; as well a pile of finely barbecued sirloin or t-bone stakes, to get them to dig 14 foot Long by 4.5 foot deep trench. Buy 3 10" sona tubes, and attachable plastic footings, as well as 1/2 to3/4 of pallet of quality premix cement. Use a suare nosed shovel to shave 3 points in the trench to undisturbed ground. Ad concrete mix if you get rained on during the process to match remaining water left over. Attach the plastic footings to the sona tubes after cutting the tubes right up to the height of where your double stacked pt 6x6's are going to laterally found the main deck construction,that's done with 2x10 pt box with 12" spacing, mix the concrete in a wheelbarrow and fill the tubes then drive a 3/4" rebar to the bottom of each concrete tube then lift each bar from the bottom by about 2" to prevent future spalling from ground moisture. Brace the tubes as required to level after you've shoved your zinc plated 3/4" inch threaded rod with 2.5" washer attached at the end about 8 to 10 inches into the concrete leaving about 1 foot to bolt down the pt stacked 2x6's when concrete has cured. Place the 2x10 deck frame work on the doubled 2x6 laterals and attach to the house to code. Sheath your deck with 2x6 cedar 1/4" spaced for expansion and prevent moisture retention. grate for up to 12X12 to 15 deck. Always use hurricane ties at ajionments to the laterals.