beam cantilever problem

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Old 05-02-18, 10:34 AM
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beam cantilever problem

Hey all, new to the forum, and I'm looking for some help/advice with a deck plan that I'm working on. Here's the scoop: This is a free standing, ground level deck, measuring roughly 18' wide (parallel to the house) by 12' deep. Originally, the plan was to dig 4 footings per 18' beam on 6' centers and do a flush beam made up of double 2x8s and use 12' 2x8 joists on 12" centers. This should have been straight forward. Here's where the problem is and I need some advice. In digging my footings, I had to move them away from the house and closer together to get away from the house foundation because the backfill from the overdig made the soil too soft, even down to 8 foot hole depth (That was a royal pain in and of itself). So I went ahead and moved my footings and improvised my plan on the fly because I was renting the auger and now I'm left with 2 rows 10' apart of 3 footings each that are on 6' centers for a total width of 12'. My improvised plan was to cantilever a drop beam (bearing directly on the concrete footings for low clearance) 3' on each side (1/4 of 12') of the footings, so I'd still have 18' wide. What I didn't take into account is that the span of the beam is measured between posts, not total length. The bigger problem is that I already have the decking which was sized to fit the 18x12 deck built to plan. I have about $4k invested in lumber and decking sitting in my backyard and I can't return it. So I need to figure out a way to make an 18' beam span across three footings that will support 2x8 joists with a 10' span and 2' cantilever on the house side. Here's the kicker, it needs to be as low profile as possible. I also don't have much wiggle room on the location because it has to serve the back door which is all the way at one end, I could lose one of the cantilevered ends but I still need that 3' cantilever on the other end. See my keyboard drawing below...

---{-----12'------}---
---O-----O-----O---
10' -
---O-----O-----O---
{--------18'---------}

I know this was a long and probably very confusing read, so I'll try to clear things up.

In my haste, I poured huge footings for a deck that's too small for what I need and I ordered very expensive materials for a very specific plan and then changed the plan.

Here are my questions:
1. how can I span 18' with the given footing spacing?
2. anybody want to come to southern Maryland and buy $3k worth of ipe decking, $500 worth of lumber, and $500 worth of hardware and brackets?
3. would it be better to just suck it up and dig/pour another footing at each end so there is no cantilever, thus making 5 footings per row on various centers?

thanks to anybody that has read this far. more thanks to anybody that has any suggestions.
 

Last edited by Kjb87; 05-02-18 at 11:03 AM.
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Old 05-03-18, 07:56 AM
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@Kjb87 I'm no pro, but I see that no one else has weighed in on your situation, so I'll just share my opinion based on what you wrote. Consider it to be about as authoritative as asking the checkout guy/girl at your local grocery store for his/her opinion.
I think you should add at least two more footings (one on each of your two rows of footings). If you want to keep the same symmetry of the deck, add four more footings--so you're adding to both ends of your rows. I know it's work, but concrete is cheap. You can keep your plan and you'll have peace of mind.
 
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Old 05-03-18, 08:20 AM
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Only comment I have is I would reconsider the 3ft beam cantilever. Even if code allows up to a 1/4 cantilever vs. span doesn't mean you should do it.
 
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Old 05-03-18, 09:32 AM
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SturdyNail, that was sorta what I was leaning towards, but it’s the digging that I’m worried about. I have a ton of concrete left over and I have a concrete mixed, so that parts easy. It’s physically getting deep enough that’s my concern.The house is only 6 months old and that backfill is soft so I’d be going down potentially 8 feet or more per hole to get to solid ground on the side by the house.

Mossman, the cantilever is much less than ideal. I’d rather be able to put the beam on the post on all four corners, but that wasn’t an option at the time I was digging the original footings. Now I’m trying to dig myself out of this predicament, both literally and figuratively.

I called the inspector this morning and his advice was to use a triple 2x12 beam and span the two outside posts so I can then cantilever the 35” in accordance with the code. The problem there is that it raises the deck too high. If I use triple 2x10s then I can only cantilever 30” but that may be enough. The frustrating part is that this beam is going to be below grade and the deck is ground level so I’m not worried about it collapsing or safety or anything, but I have to still follow the same rules that apply to decks 9 feet high.

The more I think on this the more I regret buying exotic materials that have to be trucked in. A local hardware store would have been much easier and I could just swap out what I need to change the layout. Or I should’ve laid a patio.
 
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Old 05-03-18, 05:20 PM
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L/4 of the beam span (the distance between piers) would be only 2 ft. L/o (overall span) would be 3ft cantilever... but since that is 50% more than L/4 it's not recommended, especially with a 2x8 beam. 2x12 beam would be stronger and could logically cantilever farther.

Assuming your joists are SYP, the maximum joist overhang on the house side is 1'10".

See the DCA6 deck guide for your specific application. http://www.awc.org/pdf/codes-standar...Guide-1804.pdf
 
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Old 05-05-18, 07:30 AM
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The word of the day is... CANTILEVER!

I think I may have figured out a solution... the original problem is that the deck was going to be too small which made it too far away from the house. My new plan is to attach a 2x10 ledger board directly to the solid concrete basement/foundation wall below the 2’ cantilevered kitchen and run a few 2x10 joists on 12” centers out to the beam away from the house which will be a 14’6” span, with a 16’2” max allowance and then 5 or 6 2x8s out to the closest beam to the house. This will negate the need for an excessive cantilever of the beam. The joists under the cantilevered kitchen can remain undecked since they will be mostly
obscured by the landing and totally inaccessible. I only need the ledger board to be 7‘ which is the width of the door, so then I can put a landing on top of that section and just live with the 1’ gap between the ground level portion of the deck and the house. I’ll put a bed there or something. This will do away with any type of cantilevered beam and only requires one additional footing on the bottom left corner of my diagram above.

Hopefully this visual will make sense to you guys like it does to me. In my mind the way I picture it is like an American flag where the blue field is the landing and steps to the French door, and the stripes are my deck boards at ground level. The footings are even with the bottom stripe and the 4th stripe from the top. The only difference now is the top stripe of the flag is going to be replaced by flower bed instead of deck boards since I can cantilever my joists that far. For framing, the beams will run parallel to the stripes and the joists will
run perpendicular. The 7’ ledger board will go 2’ above the top of the blue star section and the joists will run all the way to the bottom of the flag. The rest will
be 2x8s on 12” centers spanning 10’ between beams and cantilevering 2’ on the top side of the “flag” up to the missing top stripe. I was never really comfortable with putting a landing on top of cantilevered joists which sat on top of a cantilevered beam. The only footing would have been right in the center of the blue stars section. That sounded sketchy even for a guy like me.

Now I just need to find nd code guidance on attaching a ledger to solid concrete foundation walls. Do the same bolt spacing requirements exist? Can I use the guidelines for attaching a ledger to a bandjoist? I’d think my way would be exponentially stronger since it’s going into solid concrete and there’s no chance for wood failure. Do I still need any type of weather seal like flashing or anything like that? Or spacing between the concrete and wood for airflow behind the ledger or do I go solid against the concrete wall? It has a poured brick “appearance” from the forms for aesthetic reasons so it’s not perfectly smooth. Any suggestions/advice given the new plan? Also, sorry for the lengthy novel and the over use of the word cantilever.
 
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Old 05-22-18, 07:23 AM
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See figure 15 and 19 in the dca 6, mentioned earlier.
 
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Old 05-22-18, 12:21 PM
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Awesome. Thanks sleeper.

What does it mean when it says that joists shall not frame in from opposite sides of the same beam? Does that mean that one joist made up of two boards cannot meet at the same point on top of a beam? I had planned on running a 3’ joist from my ledger to the beam, then continuing out from there another 11’ to the opposite end. Do I need to get 16’ joists and cut them down to 14’ now instead of the 3’+11’ joist that I had planned on, or can they still meet in the middle on top of the beam? If I use blocking like I plan, I don’t imagine there’s be a lot of twisting potential.
 
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Old 05-22-18, 03:42 PM
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It's referring to placing joists in joist hangers on both sides of the same beam.
 
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