Building new Free standing Deck...Need Your Help!!!!(Pics Inside)

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Old 06-11-12, 09:03 PM
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Building new Free standing Deck...Need Your Help!!!!(Pics Inside)

Hey there i am building a free standing deck off the back of my house that will be 24" above grade. The deck will be 21 ft long and at its deepest point 12 ft wide..I have a few questions...
1..For the beam that is near the house it needs to be 21 ft long there is no where i can find that sells pressure treated wood in any more than 20 ft..?there is douglas fir beams that i can get at 24ft length. and apply the stuff that is used to pressure treat?And for a beam that long what size does it need to be if i am planning on using 2x8 joists spaced 16o.c and posts will be put 1 ft from both edges and spaced 5 ft apart using 6x6.
2...What is the max allowable cantilever for the 2x8?
3..How much can i cantilever a beam over the end of a post?

 
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Old 06-12-12, 03:05 AM
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Your beam won't be a single board anyway, so sistering of shorter lumber, say 12' +10' alternating the joints would give adequate support. Glue with exterior glue and screw the beam together, setting it on your posts using post-to- beam Simpson Strontie brackets.
 
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Old 06-12-12, 04:39 AM
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Is that a vent or window under the window between the doors? Will it be covered up by the deck?
 
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Old 06-12-12, 05:15 PM
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Ya that is a vent to underneath the house.i have once on each side of the house..I will not be covering it up the bottom of the deck will be about level with the bottom of that vent. and from the french doors i am going to build a wide single step that comes down 6 1/2" to the deck landing..the single door is going to be closed up and sided.
 
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Old 06-12-12, 05:18 PM
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So chandler what size lumber should i use for beams and how many thick per beam? when i stagger the joints i will have to make sure the butt ends end up on a post right?
 
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Old 06-12-12, 06:26 PM
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I'm sure Larry will be along to answer soon, but IMO, I would use a minimum of 2x10. For the beam in back I'd probably get 14's, and plan on 4 posts for it to sit on, each 7 ft apart. (0, 7, 14, 21). Your 2x10x14 (you'd need 3 of them to make a 21' beam) would be made from two overlapping pieces (14+7 and 7+14), with each joint landing on a post.

But that's just me. Seems to be a good use of materials that way.

Have you thought about what direction you'd like your decking to run? Because you'll want your joists to be perpendicular to the direction the deck boards will run. If you are expecting to run your decking planks perpendicular to the house, for example, you would probably need 3 beams, each perpendicular to the house so that your joists will be parallel with the house, as they run between the beams.

If you want your decking to run parallel to the house, then your beam will be next to the house and your joists will run perpendicular to the house.

If you run the decking at a 45, it doesn't matter which way the joists run... but you would need to space them according to the strength span of the decking you will be using.
 
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Old 06-12-12, 07:10 PM
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Brant covered it pretty well. Yes, your seam should end on a vertical support.
 
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Old 06-12-12, 08:29 PM
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hey x sleeper i am going to run the decking boards parallel to the house so all i need is the beam in the back and beam in the front, i don't need a 3rd beam in the middle right?and all i need is a double 2x10? heres a pic of a drawing with dimensions what do you think? thanks for all your help so far.
 
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Old 06-12-12, 08:48 PM
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A double 2x10 beam is fine. You shouldn't cantilever 2x10 joists 3 ft. To make that shape, I'd suggest you have 1 beam next to the house, and your other beams will be the 3 pc that form the front edge of the deck. I'd suggest your joists sit at the same level as the beams, so use joist hangers for all the joists that will be laid out in-between. They make skewed L & R joist hangers for your 45 angles.

Wait for Larry to add his 2 cents... he's probably built 10x the decks that I have.
 
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Old 06-12-12, 10:06 PM
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those angles are not going to be 45 degree angles more like 60 degree. I thought you could cantilever 1/3 the length of a joist? what size joists should i use if i want to cantilever that much?
 
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Old 06-12-12, 10:52 PM
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The IRC shows L/4 for maximum cantilever, where L is the main span distance. In your case, 3' is not allowed (being too large). Shorten your corner diagonals to make the cantilever shorter, and still use just 2 main beams.
 
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Old 06-13-12, 05:15 AM
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is a 2 ft cantilever ok????
 
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Old 06-13-12, 05:18 AM
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what is the allowable cantilever? what joist size would you guys use for this deck?
 
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Old 06-13-12, 09:40 AM
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For the L shown in your sketch (8'), allowable would be 8 / 4 = 2'. If you increase the beam spacing and joist span to 10', you can cantilever 2.5'. We can't tell you what joist sizes to use until we know the span configuration and loading conditions (i.e., if you decide to put a hot tub out in the middle, the joist requirements will be considerably "beefier" than if you just use a normal IRC design load of 50 PSF).
 
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Old 06-13-12, 03:16 PM
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well it would be 8 ft between beams the beam closest to the house will be about 1 ft from the house foundation and the joists at the widest spot would run 12 ft then taper down with the angles...i am not planning on having anything on my deck other than a propane barbecue and some deck furniture 95% of the time the only people that will be on the deck at the same time will be me, my wife and 4 year old son..oh ya and my dog. so a 2x10 joist spanning 12 feet total can have a 3 ft cantilever? is it because it is only spanning 8ft between beam connections?
 
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Old 06-13-12, 03:29 PM
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The total joist length (12') is not the same as the net span length (L = 8'). As I said earlier, a 3' cantilever for an 8' span IS NOT recommended. You will be very unhappy with the finished product. Unless you deliberately want to achieve a "spring-board" effect.
 
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Old 06-13-12, 03:37 PM
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so if i move the front beam out further so there is 9 feet between beams it should be ok to have a 2 ft cantilever? and is 2x10 joists 16 o.c. overkill? what size joists would you use? and spacing?
 
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Old 06-13-12, 06:09 PM
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Trying to consolidate all this. Your cantilever can't be more than 2' based on your joist length. Bridgeman covered that. Your last post and beam should be where you are showing it.....at the beginning of your angle and cantilever. 2x8's will span 9' without problem. Using 2x10's will ensure no bouncy bouncy. Definitely 16oc no matter what you use, since your final decking will require it. Having the joists at the same level as the beams won't allow for the overhang behind the deck, nor the cantilever. Set all your joists on top of the beams so you can effect your cantilevers on both edges and reduce deflection of the joists.
 
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Old 06-13-12, 07:07 PM
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thanks for all the help i am going to start digging for the footings...what size footings do you think i should use? i was going to use a 12" diameter and 24"deep. no frost line here. you think that would be good?
 
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Old 06-13-12, 07:32 PM
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Footing size depends on the bearing capacity of your soil, along with the deck's parameters. The IRC likes a minimum diameter of 16" for a 7' beam span (with joists spanning less than 10'), based on a 1500 PSF soil bearing capacity. If you have junk soil, you might want to kick up the size a bit--concrete is cheap. The last deck I was personally involved with (performed home owner's inspections 6 years ago) used 12" diameter footings, about 4' deep (deep frost in Colorado), with 18" elephant's paws on the bottom. The soil was a sandy, granular-clay mix, probably good for 2000 PSF.
 
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Old 06-13-12, 09:10 PM
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Ya i just looked at a chart and since i have sandy clay soil i am going with 18" diameter 2 foot deep the diameter i am gonna go with is a little bigger than what the chart says but better to be too big than too small.how much should the forting be above the dirt? and are square or cylinder footings better? do they sell 18" quick tubes?thanks for all the help i just wanna make sure i have a solid plan before I start.
 
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Old 06-14-12, 02:47 PM
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I know i got allot of questions but i need some help..
 
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Old 06-14-12, 03:39 PM
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Just don't stumble on too much information at once. Let's get the footings in. 18" round sonotubes is fine. Let the crown be a couple of inches above grade. This will keep your metal post base out of the muck, too.
 
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Old 06-14-12, 07:04 PM
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alright sounds good i will post after i get the footings in. thanks.
 
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Old 06-17-12, 12:37 PM
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alright well before i starry digging these holes i want to make sure i am not going to be wasting a ton of money and time, my concern is that the final height of the deck is going to be thirty inches off the ground so when i add the 2x10 joist to the top of the beam the posts are only gonna be around 20 or so inches. I was planning on putting two rows with 4 6x6 posts sitting on 16" diameter x 2' footings..is that way over kill should i just use deck blocks since the deck is so close to the ground? I priced out how much concrete will cost and it would be around 200 dollars that is using 5.5 80 pound bags of concrete. any opinions on these concrete blocks v.s. poured footing would be great...thanks.
 
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Old 06-17-12, 07:22 PM
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Is there a reason for your going 2' deep with the footings? Making a lot more work for yourself than necessary (not to mention the extra concrete you'll need), unless your topsoil is that deep and you want to get down past it to some decent bearing material. Frost line shouldn't be an issue in California, and the IRC only requires 12" min. footing depth. And your $200 concrete price must be the California inflation factor figured in--around here, a 90-lb. bag of Sakrete High Strength is only $3.79, meaning you'd only spend just under $10 per hole if you go with 18"-dia. footings 12" deep.

Be careful if using the trapezoidal deck blocks. They are usually too shallow to get below topsoil depth while keeping the tops 6" above grade, so you can expect some future deck settlement if you use them.
 
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Old 06-17-12, 10:20 PM
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Well i was going to do the 2 ft because my soil is really sandy/clay. i was just going to go 16"x16" but then i was like what the hell i would rather have the footings over built than to have them not enough for the weak soil...so 2' depth is way over kill? should i just stick with a 16" depth? I just wanna make sure the footings don't move..
 
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Old 06-18-12, 03:16 PM
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If you're going to worry the rest of your life about an extra 8" of footing depth, just go with the deeper depth and be done with it. Most of the rest of us wouldn't, but maybe we're just a bit older and more worn out. At least your digging should be easy.
 
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Old 06-18-12, 05:46 PM
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Ya bridge man it is reallllly easy digging here at my house...When i had to dig 8 1'x2' post holes for a fence i was done in 1hr. I have another question..would it be ok to cantilever my double 2x10 beams over the end of the corner posts about 18", I want the posts to be as tucked away as possible..Thanks a ton for all the help i apologize for all the questions that may seem a little stupid but i am the obsessive type that really doesn't want to have to go back and fix something i did wrong that could have been avoided...
 
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Old 06-18-12, 10:15 PM
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An 18" cantilever is acceptable for any member spanning more than 6' between supports. So in your case, I suspect it's OK (based on your previous sketch for span lengths). And I don't blame you a bit for not wanting to do things over if/when the first round doesn't work.
 
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Old 06-21-12, 02:19 AM
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OK -- so the left coast has finally found a little time and would like to chime in on this one.

First,peescal, there is no reason for you to build your own beams. You're in CA -- use a 4X6 for the beam and avoid all of the labor of making sandwiched beams for this thing. You will be hard pressed to find a 4X6 over 20' long, so use a 4X6X10 and a 4X6X12 (or two 4X6X12's) and have the joint in the beam occur at the center of the post supporting the beam. Lay your post spacing out so that this can happen.

Check with your local Bldg. Cept. about the required depth for the footings. They know your soil type. Clay soil doesn't require a footing anywhere near 2'. Sand does. Sand and clay are at the opposite ends of the spectrum. Which one do you have?? (WHERE in CA are you??)

Cantilevers -- you bldg. dept. won't allow anything more than 2'.

Your original post said the deck will be 24" above grade. An inch off of that for the deck boards and using 4X6's for the beam, that will only leave 17" to be filled in by your joists and your posts. Using 2X10's for you joists means the bottom of your beams will be 7" above grade. Are you SURE that's what you really want??

If I were building this deck, I would use 4X6 beams, 2X6 joists, and have posts that were about 12" tallsupporting the beams. Figure the spans based on using that size lumber at whatever spacing is involved. (I've only built about 300 to 400 similar decks in CA, and all but about 5 have been free-standing. I didn't like using ledgers under the UBC, and the IRC totally eliminated them for me!!)
 
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Old 07-06-12, 08:23 PM
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Ok so i want to cantilever the ends of my beams 2' what spacing do i need to have when it comes to post if i am using double 20' 2x10's? the total width of my deck is going to be 20'. so the spacing of the posts if i use three is going to be 5.5 ft or so?
 
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Old 07-07-12, 03:41 AM
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If you use 3, the spacing will be at center, or 10'. If you use 4, then your spacing will be reduced to 6' or so. That will be fine. I figured we'd have pictures of this deck by now
 
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Old 07-07-12, 07:49 AM
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Can I cantilever the ends of the beams over the posts 2' if i only have the posts spaced 6 feet? I know i am taking forever..I am wayyyyyy over thinking this thing.
 
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Old 07-08-12, 12:15 AM
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If this deck is only going to be 24" above grade, I don't understand WHY you are thinking about using dbl. 2X10's for the beam!! There's no need to, and you'll be placing the bottom of the beams almost at grade.

Like I said before, use 4X6's for the beams,2X6's for the joists, add more posts (which will require smaller footings. You'll have no problem with a 2' cantilever as long as the joint in the beams occurs over a post near the center of the deck and the joist is properly gussuted.
 
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Old 07-08-12, 10:10 AM
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Hope the deck gets built before the OP's grandchildren are too old to use it.
 
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Old 07-09-12, 09:37 PM
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ok so i know you guys think i am all messed up but i have made some progress...now left i know you are really thinking i am an idiot already and you probably will think so even more after i tell you my situation...so the progress i made is that i have poured my footers i am only going to have 3 per beam which gives me 8ft 2 inches between footings center to center..I had to use 3 per beam instead of 5 which i was planning to because in the other spots i was planning a post i had gas lines..sewer lines..electrical lines running.... I made the tops of my footings high enough so that my beam will sit on it not a post...I am planning on using a 20 ft 4x12 for my 2 beams..I am using this so that i know it can handle the 20' cantilever at both ends and the 8ft 2 inch span between footings.my question is where can i find a adjustable base that is made for a 4x12? I put the anchor bolts in the concrete... the biggest adjustable base i can find is a 6x6..will that work?any links or pictures would help thanks for all the help guys.
 
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Old 07-09-12, 10:31 PM
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peescal,

I'm not thinking that you're an idiot. (Never have, never will.)

Now you've encountered utility lines to complicate the project. (So much for the best laid plans!!)

As far as a cantilever, no matter what size of dimensoinal lumber you use, a 2' cantilever is all you can do. (Or at least that is all I would ever do!!)

Keep us posted on how the project progresses, and whatever problems you run into. Been there, done that with the issues you are finding out. NOW you need to get creative!!

Good luck.

Mike
 
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