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Old 05-03-2010, 01:37 PM   #1
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How to cantilever a small deck?


I'm in the conceptual design stage of adding a second floor addition above my garage. I think I'm going to place the stairs on the exterior along the wall to maximize space inside the garage (21' x 22').

I'd prefer to not have any posts supporting the staircase and deck, so it seems that a cantilever design would be logical.

If I were to utilize engineered I-joists for the new floor, it's my understanding that these should not be exposed to the elements. So that seems to preclude extending several of the I-joists beyond the exterior wall to support the upper deck for the staircase.

Is the only option to use something other than engineered I-joists for the floor structure (such as pressure treated joists) or is there a way to use the I-joists and still devise a way to cantilever the deck? Or are there engineered I-joists available that can be exposed to weather?

This is what I want to avoid:


TIA.

Tipsy


Last edited by TipsyMcStagger; 05-03-2010 at 01:41 PM.
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Old 05-03-2010, 02:00 PM   #2
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How to cantilever a small deck?


How big is this deck going to be?

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Old 05-03-2010, 02:03 PM   #3
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How to cantilever a small deck?


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Originally Posted by kwikfishron View Post
How big is this deck going to be?
I really don't know specifically, but very similar to what's depicted in the image (which is just a random photo I found online...not representative of my garage).

Not much larger than the dimensions of the door and extending out only as wide as the stair tread (about three feet, I'm guessing).

Tipsy
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Old 05-03-2010, 02:50 PM   #4
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How to cantilever a small deck?


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Originally Posted by TipsyMcStagger View Post
I really don't know specifically, but very similar to what's depicted in the image (which is just a random photo I found online...not representative of my garage).

Not much larger than the dimensions of the door and extending out only as wide as the stair tread (about three feet, I'm guessing).

Tipsy
In commercial code landings have to be a minimum of the width of the stair tread (min. 36" for occupancies less than 50 people)

The general rule for a cantilever is 25%-33% (depending on local codes) of the length of your total member span i.e. a 10' structural span will get you roughly a 2'-6" to 3'-3" cantilever. You can probably extend your TJI's beyond your building as long as they are enclosed and protected from the weather. You also have to consider that your cantilever is also carrying part of the load from your staircase.

It would probably be in your best interest to consult an architect or engineer for the design and make sure everything is permitted and inspected.
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Old 05-03-2010, 02:54 PM   #5
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How to cantilever a small deck?


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It would probably be in your best interest to consult an architect or engineer for the design and make sure everything is permitted and inspected.
I'm going to do that. I'm just trying to determine if the I-joists can be used for this purpose.

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Old 05-03-2010, 02:58 PM   #6
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How to cantilever a small deck?


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I'm going to do that. I'm just trying to determine if the I-joists can be used for this purpose.

Tipsy
The engineer / architect will be able to tell you. A lot of this will depend on your local codes and where you live. Environmental conditions in Arizona are a lot different than the coast of Maine.
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Old 05-03-2010, 03:14 PM   #7
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How to cantilever a small deck?


You can't cantilever the typical I joist used in homes out into the weather.
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Old 05-03-2010, 05:10 PM   #8
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How to cantilever a small deck?


"Unless you like bouncy construction it would be a wise decision to limit the cantilever to about 25% of supported beam or joist length. An even wiser decision would be to never exceed 3 feet of cantilever in the construction of the deck"

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