Deck footings

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Old 12-31-03, 05:53 PM
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Deck footings

Fairfax county requires 18" dia. or 16"x16" sq. footings, minimum 8" thick and 24" below grade. If I pour 18" dia. footing allway to grade, it is a lot of concrete. The largest form HD sell is 12" diag. I'd like to pour 18" diag., 8" thick footing at bottom and 12" diag. footing to grade. Does this make sense? What is the easist way to do it?
 
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Old 12-31-03, 07:38 PM
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I think maybe you have misread "below" grade, not to grade. The footer does not rise to grade...your footer is 24" BELOW grade.

16x16x8" thick 24"below grade... then your wall (post) sets on that.
 
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Old 12-31-03, 08:41 PM
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Thanks for the response. I was trying not letting the 6x6 PT wood posts contact with soil. I worried burried 6x6 PT posts may not last as long as if they are embedded in concrete or bolted on top of concrete footings above grade.
 

Last edited by yahoo2003; 01-01-04 at 11:08 AM.
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Old 12-31-03, 08:49 PM
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You can use a lot smaller building tube, maybe an eight inch on the footer to bring the concrete above grade. Yea, an 18x18x24 would be some monster deck footer... good luck!
 
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Old 12-31-03, 09:05 PM
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Should I pour the 18" by 8" footer first and the concrete column later or pour the two piece footing (footer + column) at same time. If I pour the footer and column at same time, how should I construct a form? (only tube for column available).
Thanks
 
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Old 12-31-03, 09:12 PM
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I'd pour the footer, then the tube. You'll be able to set the columns level by having a solid footer to work from. We just use the tube, but a footer under it is obviously better, but more work. Think about setting anchor bolts in the pours too.
 
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Old 01-01-04, 02:52 AM
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Go back to the Simpson catalog and look at any of the AB standoff post bases (AB, ABA, ABE, ABU) These bases will keep your post an inch off of the concrete footing. You are absolutely correct about not wanting to embed the post in the concrete or have it sit directly on the concrete.

Dig the holes. Have them inspected. Fill them with concrete and freeform them about an inch or two above grade. No need for the Sonotube forms.

I would use the Simpson AB66 -- you can embed a J-bolt in the wet concrete, leaving it about 3/4" exposed. Once the mud has set up (give it a week), then you can attach the post bases. The AB66's will give you plenty of leeway for positioning the post as long as you set the J-bolts in a straight line parallel to the back of the house. (Stretch a string line parallel to the back of the house, directly over the footings once you have the mud in the holes, and use that to locate the J-bolts.)

And a hint about digging the holes -- The inspector is going to measure the depth from grade. (Lay a stick across the hole and measure to the bottom of that.) Then he or she will measure the width of the hole AT THE BOTTOM OF THE HOLE!! That is where you need to concern yourself with the 18" of width.

Post pictures of the deck once you get it done. Would love to see them.

Mike
 
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Old 01-01-04, 05:58 AM
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Happy New Year to everyone!
webrebel, that was what in my mind.
Mike, thanks for the detailed instructions and hints. I will use J bolts and AB66s.
I have a couple of qestions:
What is freeform? Do you mean fill the 18" diameter 24" deep hole with concrete? I prefer a smaller footing top if it is strong enough to support the deck. What is smallest footing top I can have for 6x6 posts?
I'll put 5 footings, 5' apart for a 21'x9' deck and hope they will support a light weight roof or sunroom later. Is it true that most weight of roof will be supported by the footings not the ledger board, and a roof will reduce snow load to ledger board?
Thanks
 
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Old 01-01-04, 08:18 AM
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Fill the 18" X 24" hole with concrete. Adding a small footing on top of that is fine. You could use 2X4's and make it an 18" or larger square, or, if you want it round, use the plastic bender board to form it, (again, at least 18" in diameter).

Check with other bldg. supplies (besides HD) -- Some will carry a Sonotube 18" or larger.
 
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Old 01-01-04, 08:29 AM
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I made my footers so they came up out of the ground about 5". And have my deck bolted to it. Cost a bit more in concrete, but I have no wood making direct ground contact. If rot ever takes place I can easily repair it.
 
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Old 01-01-04, 08:36 AM
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Lemme get this right...you guys dig a hole 32 inches deep (24'' plus the 8" footer), 18 inches square and then FILL the hole with concrete? For a deck footer? I'm tired just thinking about it....
 
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Old 01-01-04, 08:41 AM
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Adding a room or a patio cover at some point in the future is certainly an option. Since the cover would probably be mounted in a hanger on the house wall, it would technically reduce or remove the snow load from the ledger (but the bldg. depts, at least around here, don't see it that way.) The room, with the side walls still sitting on the deck, really wouldn't, at least not to the same extent.

If you do decide to add this on later, put the posts of the cover, or the outside wall of the room, directly over the beam that is supporting the deck. What I do when installing a patio cover on a deck is either cut through or remove the deck board(s) directly over the beam and set the on the beam (then reinstall the deck boards), or at least block between the joists where the posts will be, with the blocks sitting directly on the beam.

With a room sitting on a deck, adding the blocks is all that the bldg. depts. around here ask me to do.
 
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Old 01-01-04, 08:43 AM
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Originally posted by webrebel
Lemme get this right...you guys dig a hole 32 inches deep (24'' plus the 8" footer), 18 inches square and then FILL the hole with concrete? For a deck footer? I'm tired just thinking about it....
You think thats bad? In my neck on the woods the frost level is 48". Needless to say I rented a BObcat with a posthole attachment . I borrowed a buddies cement mixer. Had 14 footers done 2 days. One day to dig the holes and get them inspected, the next to mix and pour. I used 12" tubes by the way.
 
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Old 01-01-04, 08:53 AM
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webrebel,

yahoo2003 is dealing with frost -- THAT'S why his footings have to be 24" deep. Not sure how far above grade his deck will be, but if the bldg. dept. is requiring 6X6 posts, it must be quite a ways up. That leads to the footings being 18" in diameter.

It's a lot more than I have to do for a deck around here (frost isn't an issue, usually), but for some of the patio covers or rooms I've installed, the footings have to be even larger!! (MY sunroom has 2 footings (the corners) that are 24" sq. and 42" deep, with the posts (aluminum) of the room buried 36" into them. Reason is wind load and earthquakes, and because the room projects out from the house more than it's width.
 
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Old 01-01-04, 09:04 AM
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We have the 24" frost line too. And the 8x18 footers are not unreasonable, but bringing that 18" width of concrete another 2 feet up for a 6x6 post is overkill by a mile. Around here 9" thick pour is average for basement walls 8ft high. If I'm understanding this correctly, your pouring twice the amount for a deck post as you would for a HOUSE.
 
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Old 01-01-04, 09:22 AM
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Well, NOT HERE!! I don't have to embed my footings 24" deep for a deck. This is Sunny CA -- frost isn't an issue!! As long as my deck footings are 8" deep, I'm below the frost line in all but a few sq. miles of this state. (And decks can't be built in most of those miles!!)

Patio cover footings are an entirely different issue. Have a lot fewer of them involved, so they have to be bigger. And then there is the wind load that comes into play on them that doesn't exist on a deck.
 
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Old 01-01-04, 11:07 AM
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Thanks for all your inputs. The requirements are in this web page:
http://www.co.fairfax.va.us/dpwes/pu...ns/deckdet.htm
My deck is only 4' high.
Fairfax county specifies one post size (6x6) and one footer size (18" round or 16" square) for all.
Minimum requirement is 8" thick footer with 6x6 post burried.
I figured out I'll need about 6 bags of 80lbs for 18" round 24" deep footing.
The wieght of a 9'x21' sunporch is 700lb (www.sunporch.com) which will add about 4 PSF dead load.
I don't know how to calculate wind load.
 
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Old 01-01-04, 05:59 PM
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Yahoo2003, don't feel bad. I have no clue how to calculate snow load or wind loads either. However, I DO know how to read the engineering cut sheets and all of their tables that apply to all of the patio covers and rooms that I install. Whatever they tell me to use for footings is what I use.

And I don't argue about it very much either, except when I'm really close (a half mile or less) to the south boundry of Shasta County, and the inspector (or plan checker) tells me I have to use the 30# snow load table. If I move just a little south, (sometimes as little as 100 YARDS!!) into Tehama County, the snow load I have to use is only 10#. THAT changes everything! Smaller footings, longer spans, ...

That's OK -- they DO let me cheat a little now and then in that area if I really press the issue! (They know me!!) And, we both know that they COULD drop the snow load in that area to 20# and it would still be overkill.

You pulled the permit to build the deck -- I'm proud of you!! Now you have to build it to whatever requirements the plan checker and the inspector lay down. It can be a hassle at times, and it will certainly cost a bit more and take more work. That's OK -- the deck will be safer and will last longer, AND you won't have any problems if you ever sell the house.

6X6 posts for a deck that's only 4' above grade? If they say so, that's what you use. (See, there's part of that additional expense.) I could do that deck HERE using just 4X4 posts!!

And I didn't totally understand your footings at first, but I'm beginning to! If they will let you bury that 18 X 18 X 8 portion so that it is 24" deep, then let you use a 12" Sonotube to extend the concrete so that it's a few inches above grade, and you attach your posts to the top of that, go for it. You still got the digging to do, but you save a chunk on the cost of the concrete.

Mike
 
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Old 01-01-04, 07:21 PM
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Mike
Materials won't cost much more if I use 6 bags rather than 3 or 4 bags per post ($3.44 per 80 lb at HD), it is labor to haul, mix and pour concrete. I have not applied permit yet. I only studied their requirements, talked to plan reviewer over the phone and talked to some contractors. I got feeling the reviewers will be tough if anything is different from their "Typical Deck Details".
I still like a freestanding deck because I could build a deck at any height. My first floor has 2' overhang that can't be used to attach ledger board by code. Attaching ledger board to foundation wall will make my deck 8" lower than thresholds of doors.
I'll attach some photos next time.
I'm not in hurry to build the deck, I want to build it right.
I don't know anything about deck a month ago, I have learned a lot from this forum about deck and more.
Thanks a lot.
 
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Old 01-01-04, 08:28 PM
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Posting pictures in here is tricky. The easy way is to put them on a personal website (Yahoo, Angelfire, etc.) and simply post the URL to the site.

I was wondering about your building a deck in the middle of winter. That's OK -- build it in your mind a half dozen times, and when you ACTUALLY get to it, it will be easier.

An 8" step coming out of the doors is right at the legal maximum. If possible, I would probably try to find a way to reduce that to about 7-1/2". It's just more comfortable. That 1/2" doesn't sound like much, but trust me, IT IS!

Just keep brainstorming, and don't hesitate to ask the questions. (I've noticed you haven't been shy about THAT!! ;-)) That's Ok. That's what we are here for, and getting the 23rd opinion never hurts.

Mike
 
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Old 01-02-04, 08:47 AM
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Mike,
I'm trying to attach a photo,
www.geocities.com/myfirstdeck/House1.JPG
I don't know how to make the link "blue" so you can click on and open the picture.
The photo shows the 8'x21' slab and overhang I talked about.
 

Last edited by yahoo2003; 01-02-04 at 08:58 AM.
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Old 01-02-04, 03:20 PM
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Guess it doesn't matter that it's not blue. I simply copied the URL and pasted it in the 'go to box' and got there.

No surprises in that picture -- it was as you described and what I envisioned.
 
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