Pouring Concrete Footings and Piers
I need some help….
I have 9 footings/piers to pour for a deck. About 1.5 – 2 yards of concrete. I’m a rookie when it comes to concrete. I don’t have direct access for a truck to pour directly to the forms so anything ready mixed would have to be wheeled in.
The footings are 2 feet in diameter and about 18″ tall. The piers would be 12″ diameter (Sonotubes) and about 25″ – 30″ tall.
I’m looking at basically two options – Ready mix and mix on site from bags.
Ready Mix – How long do you have to off load from the truck and the cement is still good? I was thinking of using a “Georgia bucket” (motorized 16 cu ft wheel barrel). One concern I have is pouring a footing that is wider than the pier at the same time. Would the concrete mushroom up from the bottom? Also, can 2 or 3 guys compete 9 footings/piers in time for the concrete not to set on the truck?
Bags – I know this will be the most labor intensive. But, spreading the work out over a week in the evenings was what I was planning on doing. My calculations come to about 50 80# bags! I was planning on pouring the footings and adding a couple of pieces of 3′ rebar. Let the footings set and then come back and pour the piers. Would the rebar tie everything together ok?
Any advice would be VERY helpful!
Are the piers in the ground or above. I ask because if it's in the ground I would pour the footings, then set the sonotubes and backfill before pouring the piers. If it's above the ground I'm not sure but you may have to fill them in stages, as 30" of wet concrete would be enough to blow out the bottoms. I may be wrong about this, others will surely correct me.
In your situation I would do it in bags. In another recent topic there was mention of 90 minutes working time from the truck, which I don't think is enought time for what you're doing. Also, what you're doing would be in stages. You mentioned spreading the work out over a week after work. Seems like a good idea, or over a weekend with some helpers.
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Ted - the footings are in the ground. Thanks for the feedback.
I was wondering if the piers are in the ground, but you get the idea. Like I said, others have a lot more experience with these matters and will no doubt be along shortly. :)--------------------------------------------------------
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I'd use bags. Less stressfull because you can work at your own timetable and not be concerned about weather and unforeseen contingencies. A cement mixer would be nice to have. We would usually pour stuff like that in one shot (ie. footing and post at same time) backfilling as we poured. You can buy one piece forms or you can improvise on site.
On more question. How do the building inspectors confirm that the holes are deep enough? They must be on "solid ground". I've heard that they drop a piece of rebar in the hole and if it does not stick up then you are ok.
I'd rather not have the inspectors come out twice... :)
I just poured piers/footings for front porch entry post bases using 12" sonotubes. I poured a 2'x2'x6" footing at virgin/undisturbed soil height (in my case @ basement excavation level) left a rough finish on the footings with just enough of a screed to get fairly level. In the footing I built a little "mesh" of rebar scraps and also added a scrap of wire mesh. Stubbed in 3 pieces of "L" shaped rebar about 8" above the footing and let it cure for a couple days. Then I plumbed the sonotube and backfilled around it to ensure it didn't move or blow out. Cut rebar to length, made a PVC pipe collar to drop over the rebar and catch the stubs out of the footer and poured a full 6' of sonotube straight out of the truck with no problems. Suspended the simpson post base from a bracket off the house and vibrated very little with the shoe of my sawzall. As far as inspectors - I don't have any so no real advice. I think getting below frostline(if applicable) and designing enough footprint is most important. A stake could be driven to test compation at the bottom of the hole if you were worried. Just a guess.
How do you get that inspected if you've backfillrd? Now you see this one-eyed midget
Shouting the word "NOW"
And you say, "For what reason?"
And he says, "How?"
And you say, "What does this mean?"
And he screams back, "You're a cow
Give me some milk
Or else go home"
Constructing a large pier borne multi-floored structure would be a different scenario but when building decks, frost is the major concern here. Hole depth and shape is what we focus on. Weight of the deck, seismic and wind loads never seem to be a major concern . I don't recall the inspectors ever displaying any interest in looking at the sonos.
One inspector said he knew we were out to do a good job while others were just trying to cheat him and cut as many corners as possible. Having the respect of the local inspector is good.
Edited 6/22/2008 2:21 pm ET by sisyphus
Use bags, and rent a small electric mixer.
You'll be able to easily mix and pour in a 1/2 day or so.
Its even better if you can get the bags of concrete delivered to the site, saves time and work.
For the inspectors be suire to know aht they expect to see when they come to check the empty holes.
For the CC I like to use a rented mixer, either the gas ones if I can back the truck up to the spot or an electric one which can be set right at the the hole you're going to dump it in.
2or 3 guys would have no problem pouring those piers from a truck.As for your forms put lids on the footing forms, just drill hole or cut notches so you tell if the forms are full, vibrating will help. The swiss hammer method is used for testing solid ground. The inspector has a rod about 7' long pointy on one end, as liding weight a the top with a stop on it. The weight is raised and dropped a certain number of times(sorry i dont recall the number) and the amount of penetration is measured( don't know that either it has been awhile since i have been on a job like that, mostly millwrighting now) He will usually test a number of spots and pass or fail you. Always be nice to that inspector, they can ,ake or break you, quick.
I didn't see anyone else mention this so I will.
Order 1.5-2 yds. of redi-mix and you most likely will be paying a short load charge, here that means a 5 yard minimum charge.
Makes sack mix look down right easy and cheap in comparison.
The short load charge is often true but the site mix guys usually don't care - may have a hourly standby like our local site mix.
About 5 years ago I was hired to make a handi-cap access ramp up the side of this ladies house and because of the location of the house, couldn't get a crete truck out. So we hand mixed 100 90# bags. There were 2 of us and it only took 6 hours. Our system worked great. We lined all of our bags up and tore the pour spout out and had 5 buckets lined up. 5 gallon buckets have exactly enough room for the crete and water with just enough room for your mixer(mud paddle and the biggest drill you got)
I'd mix and the laborer would dump..It goes alot faster than you'd think...If you don't think you can pour footer and pier at same time the rebar should tie the two together just fine. But I would tie the bar from the footer directly to the bar cage in your sono
All I ever wanted in life was an unfair advantage...
Those sound like some serious footings for a deck, but it shouldn't move..........ever!! - lol
Since the footings are in the ground, I think that I would dig them out at 24" diameter and 18" deep and let the ground be my "form". I would just pour the footings and stick 2-3 pieces of ~36" long rebar in the wet concrete so they will be in the sonotube when your pour the piers. When the footings are in, you can fine tune your pier locations, set your sonotubes, and pour the piers.
If you have one nearby, check into those small concrete buggys. They're pretty handy if:
>> The footings are 2 feet in diameter and about 18" tall. The piers would be 12" diameter (Sonotubes) and about 25" - 30" tall. <<
Are you saying that you are going to have footings with piers on top of them? Also, are you saying the footings are going to be 18" thick? Maybe I'm mis-understanding but generally 8" thick footings are thick enough to support any deck unless you have a soils issue with engineered footings. 2 feet in diameter is pretty darn big too. 18" x 18" would be more standard.
problem with bag mix is, that stuff is only about 1800-2500 psi and you have to breath all the dust. It you add of all the bag you will see its cheaper to buy from the concrete supplier quicker on time, back, and money. Most job like 99% of them wont let you use bag mix.
I agree w/ Matt ... 24x24x18 sounds like overkill. the 12" sonotube alone may provide enough ... this is a deck, not a house. A 12" sonotube column is a huge column for just a deck. To reduce your effort/expense ... i'd double check your structure ... I think you're making too much of it. If you are taking the advice of Friend Fred who can only think in overdesign mode, then you could be going overboard.
Don't forget rebar in the footing and/or column ... that's the most important thing in concrete. I would avoid sticking rebar in the ground to support it until the pour ... you're asking for possible problems long term (rebar technically is supposed to have 1 1/2 inches of cover).
Guys - I checked the county specs. The footing for my joist/beam spans needs to be 24" in diameter and 10" tall. I also have to use 6x6 posts so I was thinking that the 12" sonotube would be the right size to give ample space on the sides. The holes look like they will be about 40" inches deep based on one of my holes.
I used an auger yesterday to dig out the holes. The auger was only 12" wide and I was able to get it to about 32" deep. Later this week I'm renting a Toro Dingo with a 24" auger to finish things off. I should have done that in the first place. Don't ask me why I didn't! :)
The bigger issue is 3 of the footings are in softer soil at 30" deep. Hopefully in a few more inches I'll find solid ground.
sorry, still skeptical here. Am I missing something? 9 piers ... how big of a deck is this?.
10" deep is a LOT shallower than 18". and 24" diameter is definately smaller than 24" square. 12" diam sounds like your choice ... that's big for a 6x6 wood post.
Frost depth should be no more than 36" ... to the bottom of the footing. 10" footing means a column that is 26" + 4-6" ... so your 30 inch would be fine if on 10" footing.
If 3 footings are on what you say is softer soil, then a spread footing may be worthwhile.
It may be worth paying an engineer a few bucks to knock out a footing design. I know that sounds like overkill ... but no more than what you are already doing.
Where are you located? Maybe you got mush for soil and need these footings?
I'm in Fairfax, VA.
The overall depth of the footing will be around 40 - 48" below grade. The county state that they must be set at a minimum of 24" below grade and on solid ground. I've been testing solid ground by dropping a digging bar about 6 - 10" from the bottom. If it stays upright then I'm assuming it is not on solid ground.
Usually the requirement is stated as 'on undesturbed soil'. 40-48" is pretty darn deep for a stinking deck! :)
And 24 x 24 is a huge spread footing for that ... you could float that on top ... but you don't want that, either.
Good idea to have the BO call the shot. You can tamp the soil to be more compact and therefore allow you to go only to the minimum frost depth (24-30" I'm guessing down there).
Hope you can scale it back and save some expense and effort. To avoid the same depth as foundation, you might draw a 45 angle from your existing and set your colums up higher and out further from the exsiting. This results in a cantilever deck next to the house - a couple of feet could buy you some relief.
BTW ... I built my new house on 'solid ground' ... or undisturbed soil ... I'd bet a digging bar would definately have stuck upright. It's still solid ground, though (by structural definition). It is stable ground in that it isn't near e.g. a steep slope where heavy rains might cause undermining ... I suppose there could potentially be all kinds of situations where 'std' requirements wouldn't work.
Just remember ... it's just a deck and anything that happens is probably easily fixed (relatively speaking).
Hi Mike - I grew up in Fairfax ... a long time ago (1961-1973). For light concrete work around the house, including up to fairly signficant pours (like 35 bags on my own) I bought a two-bag mixer on ebay - this one or its equivalent - http://cgi.ebay.com/GIANT-CEMENT-MIXER-8-CF-CONCRETE-MORTAR-STUCCO-BIG-DRUM_W0QQitemZ310060908637QQcmdZViewItem?hash=item310060908637&_trksid=p3286.m14.l1318 Works great (cost me $325).
is it a requirement that the posts be set in CC? They'll last a lot longer if you just set them on the footings and backfill with either tamped gravel or dirt.
John - the plan is to have concrete piers tied into the concrete footings. the footings/piers are about 40-48" in the ground. I will put the 6x6 posts on a galv post bracket tied into the pier with a 1/2" bolt.
Clewless - I might call the BI tomorrow to see if I can get them out to just check for the footing depth. If I need to go to a spread footing I'd rather not have to rent something twice to dig holes. I'm assuming a spread footing would not be as deep but would probably run the length of the 3 footings in question.
The funny thing about Fairfax county is they have a new requirement that footings closer than 5' from the foundation wall must be set at the same depth as the foundation. They are concerned with extra load bearing on the the foundation walls.
All I want is a STINKING deck!!!! :)
BTW the deck is 15' x 32' and elevated by about 26" off the ground.
Edited 6/22/2008 6:09 pm ET by Mike126
I used to live in the People's Republic of Fairfax County... I know the Gestapo is a little crazy there. I guess they must have had some significant deck failures though. Probably the reason for requiring the foundation deep footings for footings within 5' of the house is that they don't want any weight bearing on backfill as backfill is not virgin dirt.
How about a quick sketch of the deck/footing layout? Something in M/S paint or what-have would do. I looked at the Fairfax web site and I'm having a little trouble guessing how your footers are to be laid out. Nine footings seem to suggest 3 rows of 3. Is the deck supported by the house on one side or is it essentially a free standing deck?
I've built a number of decks and a 24" dia footing is crazy-big. That is the size we use for house support piers. I see their chart though.
I've never head of testing soil in the bottom of footers that way... I use a probe rod as do all the BIs I've seen. Most soil engineers too. I have one something like this. Obviously I'm not suggesting you go buy one to build just one deck. You can fake it with a piece of 1/2" or better still 5/8" rebar though. Take a file or grinder and fashion one end of the rebar rod into a dull point - something like a bullet. I guess you could even make a wooden 'T' handle if you wanted but that might be optional. Take the rod and press it into the dirt using your weight. If you can press it in for more than an inch or so you have soft dirt and need to keep digging. You don't have to use all your strength - just lean on it. Unless you are a 85# teenager girl :-)
Guys - since a picture is worth a 1000 words and then some... :)
The first drawing is of the lower joist section. The 3 footings in question are the ones closest to the house. This may have been where the excavator built their ramp to exit the basement with digging the original foundation.
To avoid putting my footings at the depth of the house foundation, I'm putting in a ledger under the breakfast room cantilever bump-out.
The second drawing is the main joist section
The third drawing is a cross section of the bump-out and ledger/joist system.
That is a fairly atypical method to frame a deck. I can follow your thinking though because of the 8' deep footer requirement up next to the house. Do you already have it permitted that way?
Is the idea to run the deck boards at a 45º angle so the change in joist direction won't be an issue?
Back to the issue you asked about - the footers - without getting too detailed - if the 2nd to the left footer was moved to the left 6" the largest footer you would need 18" in diameter as your longest beam span would be <8' and your longest joist span would be ~12' - that from the table shown on sheet 8 of the document on the FFX Co web site.
If you want to use bag mix concrete as stated above the problem is inconsistency of the product. I'd just buy a bag or 2 of Portland cement and add a shovel of that to each bag of concrete. To illustrate my point about inconstancy today I bought a bag of quickcreet (sp?) concrete mix and it didn't have any gravel in it! It seemed to be the wrong product in the bag - like maybe it was pre-mixed mortar or topping mix. Weird!
Matt - Good point. I should have caught that in the initial plan. Actually if I do that then all of my footers can be 18" diameter x 8" thick.
Either way I'm bringing in a Dingo with a 24" auger to finish my holes.
I'll probably stick with the 24" holes. Better to over build then to under build.
I did get to talk with an inspector today. He said to check the holes using a #5 rebar and push into the ground. If it goes more than 3" then I'll need to keep digging. I'll try to schedule my footing inspections for Thursday afternoon while I still have the Dingo. He said I do have the option of using a spread footing but they would want an engineer to sign off on it.
I just went out the check my holes.... We had a fairly good rain. I covered them up with some plastic. A few had water in them so I guess I'll need to pump them out. I also did a solid gound test and it looks like I'm good. I only had a couple of inches on penetration... I'll keep my fingers crossed.
Edited 6/23/2008 8:07 pm ET by Mike126
Edited 6/23/2008 8:09 pm ET by Mike126
BTW the deck is 15' x 32' and elevated by about 26" off the ground.
You can easily calculate the required footer size.
15 x 32 is 480 square feet, multiply by 100 psf, 48,000 load support required.
Assume 2500 psf soil, means you need 19.2 square feet of bearing surface.
A 24" diameter footer has 3.14 square feet of bearing surface - so you need 7 piers.
So your 9 piers with 24" diameter footer sounds about right - definitely not overkill, it's tough to do symmetrical spacing with 7 piers.
This is a freestanding deck, right - it's not attached to the house? If it's attached to the house, that raises a whole set of other issues, but reduces the pier requirements. It's better to do it freestanding rather than attached, if you can.
Edit: Just looked at your drawing, and saw the ledger attachment. How are you planning to attach the ledger? It will take far more support than anyone will tell you, and they will tell you it is "overkill" if it is done right. Can do more calculations to confirm, but generally a deck with that load would need 1/2" rods epoxied into the concrete block wall in a staggered pattern 8" to 12" on center, and at least a 2x12 as a ledger.
Edit 2: Just looked at your drawings again. What is your foundation wall? If it's not solid concrete, expansion anchors won't be reliable. It also appears your ledger is significantly undersized. Who engineered the deck? You may want to ask the PE to check his calculations. Do you have a fastener schedule for the ledger?
disclaimer: This is not engineering work and I am not acting as your PE.
Edited 6/23/2008 8:40 am ET by woodturner9
Edited 6/23/2008 8:43 am ET by woodturner9
I did the drawings and engineering based on the county design requirements. the ledger is attached to both concrete (the smaller section off the breakfast area) using 1/2 galv. wedge anchors. The spacing for those are 29" o.c. stagered rows. I added a few extra. The spacing for epoxy achors is around 24" o.c. acording to county specs.
The lower ledger at the breakfast area is a 2"x8" with 2"x8" joists running 10'. This is within the county requirements.
The main ledger (the rest of the deck) is 2"x10" and the joists are 2"x10" running about 15'.
Beams will be 2- 2"x10"s
the ledger is attached to both concrete (the smaller section off the breakfast area) using 1/2 galv. wedge anchors. The spacing for those are 29" o.c. stagered rows.
Here is the spec table for red head wedge anchors:
4700 lbs at a 2.25 inch embedment in concrete. That's an ultimate value - they specify to use 1/4 that as a design load.
So let's say 1100 lbs per fastener. If your 32' dimension were a straight ledger, given that you need to support 24000 lbs, you would need 22 fasteners, or one every 17".
If you are doing 29" in staggered rows, which I assume you mean two rows where the fasteners in each row are spaced 29", then you have a fastener every 14.5" - so that should be OK.
Be careful using the county rules as design criteria, though. Those rules are based on specific situations, which may not apply in your case. In addition, some of their specs appear to be a bit "light".
Keep in mind, too, that not all wedge anchors have the same load ratings - Red Head has different numbers than Simpson, for example. Since you are using PT wood, you will need to use stainless steel anchors, BTW - carbon steel corrodes when in contact with the new PT formulations. Hot dipped galvanized MAY be an option, if you can find wedge anchors that meet the galvanizing spec for PT wood use, but I would stick with stainless stee.
Just because the county will approve it doesn't necessarily mean it's safe. The deck collapses we keep hearing about in the news were decks that were built to code. In the last couple of years there has been growing awareness that deck design rules are inadequate - and not every municipality has fully upgraded their specs yet.
Would it be easier to run a couple posts down to the footing next to the basement wall? Bob's next test date: 12/10/07
Jim - That would require that I put the footings at around 8' deep (foundation elevation/depth). I also have a rather active sump pump when it rains so I was not thrilled about going that deep and then having to go deeper after hitting water.
Edited 6/23/2008 10:33 am ET by Mike126
If you already have a water concern at the basement due to the sump running often, you ought to reconsider the orientation of the deck boards to run perpindicular to the house and the joists running parrellel. With the decking running away from the house, proper slope will take it even further. With the decking running parrallel you can only take the water to either side of the deck.
Would it be easier to run a couple posts down to the footing next to the basement wall?
That is often an option.
Ledger attachments are the most common failure point for decks. There isn't anything inherently wrong with them, it's just that they are often undersized and aren't properly attached to the structure.
If it were an elevated deck, I would drill to the footer and pour new footers and piers. It only has to be to viable soil, though - so if 3' is the frost depth and the basement backfill was properly compacted and has been in place long enough to be viable, you could just drill 3' down for the new footer.
In the OP's case, though, he is only 26" off the ground. So if the deck collapses, it's unlikely anyone would be seriously injured. So, in his case, the ledger attachment doesn't concern me too much - he has a concrete wall to attach to, and appears to be using sufficient fasteners to be safe. I'm not suggesting his deck will collapse - it sounds like it should be fine - just saying that if it did, it isn't a big deal like it would be if it were 10' above grade.
Jim / Woodturner - I'll probably add a few more anchors into the concrete wall for the ledgers. It can't hurt....
Considering how the old deck was built that this is replacing and the fact it lasted 25 years without collapsing, what I am doing is about 10 times stronger. The old deck had footings at 24" below grade and in some cases no footings just posts buried in the ground.
I removed the old deck to make repairs to major wood rot around the breakfast bump-out. Once I started to remove it I kept finding issue after issue with the original construction. A classic money pit!
The actual way to size deck fooings is by finding the tributary area for each. Sounds like Fairfax County thought that was too complicated so they want to use the table shown on page 7 of the link I posted above.
Edited 6/23/2008 6:55 pm ET by Matt
We just finished pouring the footings/piers for the cottage deck , the deck will be 14' x 32', we have 4 footings. We used the big foot with the 10" sonotube. we had the excavator dig a full trench below the frost line.. Leveled out the footings then braced the sonotube against the walls so nothing moved. mixed 32 bags of cement in a small cement mixer run by the generator. worked perfect. we put gravel down then added french drain around each footing and connected this to the draining system. Added another layer of gravel then cloth then gravel then back fill.
Congratulations. You are probably the first person in the history of deck building to put foundation drains around deck piers!!!
I guess if you already had a trench dug, it wasn't that much more work.....
Is there something wrong with this.?? We were advised due to the freeze thaw and so much water around the footings that this is common practice in northern Ontario.
No, nothing wrong with it. But probably not needed-though I could be wrong.
It's been recommended by the excavator and the building inspector had also sujggested it. No it wasn't much more work, didn't cost much more, just added more protection to the footings since the drain was layed out right around the footings with conectors attaching it.
WIth the amount of rain we get and the amount of snow we get, since the trench was there, it will keep the footings dry then why not.