18" high deck - cantilever or flush beam

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Old 01-29-19, 09:39 AM
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18" high deck - cantilever or flush beam

hello, I am designing a deck I plan to build, that is ~24'x20'
It is 18" from grade to the base of the door that would lead to the deck
Short question - should I do cantilever with smaller boards, or flush beam use 2x10 s?

Long question - there's a kitchen bay that complicates the flush beam (see picture - black line is the house)

I have an area at the end where ideally I would like to have a cantilevered area past a bay. So would have beam in front of bay and cantilever 1' 6" past either side of the bay.

However, with this deck height is that possible? I don't really want to go below 2x8 for the beams or joists. Or would 2x6 be ok, and would enable the use of post, beam, and joist, and then the cantilever?

At this height is the only option the flush beam , in which case I can't do the cantilever?

I am considering using helical piers, so might be able to get closer to foundation, but with concrete or helical i wont be able to get close enough to frame a flush beam there

I don't want to use a ledger board either, which I know might help here. We have a brick facade and I just don't want to risk the potential for providing a water channel into the house framing etc later on.

Any advice appreciated! otherwise I need to convince my wife she really wants a patio...

added potential stack up if I use a drop beam...
 
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Last edited by northwood9; 01-29-19 at 11:03 AM.
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Old 01-29-19, 09:52 AM
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This guide may help you out. (See figure 5... and instead of a ledger, that will need to be a beam that is spaced away from the brick) Depending on the width of your bay, additional piers and posts could be added.

https://www.awc.org/pdf/codes-standa...Guide-1804.pdf

Due to your low height, I would try to do flush beam everywhere rather than doing joist over beam. (See figures 7, 8a, 8b) The problem you will encounter is that your footings next to the house need to be on undisturbed soil meaning they need to be just as deep as the house footing is. (See Footings R403 and figure 12)

And yes, a patio would be much more practical with less long term maintenance.
 
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Old 01-29-19, 11:02 AM
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thanks, very helpful. Using figure 5, to have a beam instead of a ledger by the house (if doing flush beam), then that would mean a pier right next to the foundation, as you can't cantilever the flush beam? so I think flush beam might be out unless I was using a ledger

I am trying to attach a second drawing of the stack up to the original post...If i used a dropped beam, i could come out up to 2 ft, and using the 2x8 joist cantilever into the area around the kitchen? 2 questions
1) is 3" enough post before it gets notched, will it split? could go 6x6 if needed
2) can you have a joist that is larger than a beam.. 2x6 beam, 2x8 joist

Probably making it harder than it needs to be, but don't see a way to get around it with the current deck height. If I use helical piers, the guy said he would likely be going down 10+ feet anyway due to heavy clay here... so if I can get a pier within 2' it would work
 
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Old 01-29-19, 11:13 AM
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There is nothing wrong with having a pier next to the foundation, you would just need to pin the new and old footings together with rebar and make the new footing the same height and thickness as the existing footing... (even if it means the post will be half on the original footing and half on the new pier.)

You can only use 6x6 post or larger according to most current codes, fyi.
A 2x6 "beam" is not much of a beam unless you plan to have piers and posts every 4 feet... see table 3a, where the spacing of the piers gets closer as the span of the joists gets longer.

A joist can only be larger than the beam if it is joist over beam.
 
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Old 01-29-19, 12:05 PM
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thanks again, I should probably give up on trying to figure out the cantilever to get into that space. To pin a pier to the foundation I imagine would get expensive quick, its Illinois so 4' frost line minimum, plus the foundation wall is an 8ft basement. so that would be a deep hole + the rebar and concrete preparation

will think around how a flush beam could get in there... or just not have those 2 inlets/cantilevers as deck and make some big planters to fill the hole or something
 
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