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I'm designing an addition onto my existing deck (the existing deck is not pictured below). The addition will be roughly 20' by 15', and I'm planning on making a portion of it a single step lower. While it will butt up against the house, the deck will be self-supporting (I will not be tying into the house for support). The overall profile I'm looking for is this:

Top of the deck

My first thought was to frame both levels completely independent of each other, like this:

Complex framing

The obvious issue here being the large number of angled cuts in both deck bands and the complexity of getting beams (not pictured) in proper locations. My second thought was to build both decks as rectangular as possible (the cutout at the left side is for the bay window on my house, so it has to stay) and build a platform on top of the lower portion to create the angular top profile like this:

enter image description here

To make it clear what I did, here is the same design with the new platform moved to the side:

enter image description here

My question is, putting aside local building codes (which both appear to meet, and I'll definitely be getting a permit), is the second design reasonable? Is one better or worse than the other from a structural or safety point of view? Also, not to ask too many questions, but would toe nailing the additional platform to the joists/deck band of the lower platform be sufficient, or should I use brackets to join them together?

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My only concern with the second is if there is differential settling between the two decks, you might get a tripping hazard between the upper deck and the false deck. – Chris Cudmore Feb 11 at 18:08
@ChrisCudmore: Thanks, that's a good thought. I do plan to bolt both deck bands together to try to mitigate that, but notching out some support posts to go under the bolts might be a good idea, too, to support the point load. – Adam Robinson Feb 11 at 18:23
How high off the ground are these decks? Threaded fasteners, not nails need to be used. IRC requires bolts or lags in some locations. Not sure, but adjacent hanging decks may meet that requirement. Threaded is always better. – shirlock homes Feb 11 at 23:24
Where are the supported beams going? – shirlock homes Feb 11 at 23:25
@shirlockhomes: Roughly around 2', 3' maximum off the ground. I need to go out and measure (the yard is sloped). The beams I left off since I'll build them to code, but in general there will be one right up against the cutout on the far side (for the bay window), another near the step on the upper section, one near the step on the lower section, and one close to the end on the lower section. I will try to upload a drawing with the beams in place this evening. – Adam Robinson Feb 12 at 14:55

3 Answers

up vote 3 down vote

The second on is a better choice; in the first one, you have a lot of angles that will make it hard to carry the loads effectively. I would probably go with a 2x6 for the platform on the second deck to get your shape; that will get you 5.5" of difference in height. You could also go with a 2x8 for a 7.5" difference. 2x4 only gets you 2x4, and 3.5" is too short to meet code for a step.

It would be good to see the beams to comment on the overall structure.

Think about lighting for the edge so that you can safely see the step at night.

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Thanks; yeah, as pictured it's 2x6, but I have not decided if I'll go 2x6 or 2x8. I will try to modify the file with beams in place and upload an image this evening. – Adam Robinson Feb 12 at 14:56
up vote 2 down vote

First off, I would avoid the step if at all possible, you are really cutting the functionality of your deck down by adding it, plus it is a tripping hazard.

You can visually separate the sections of your deck by changing the decking pattern and colours.

However, if you are dead set on the multi-level design then the second way is the obviously easier choice. I would make sure to bolt the small section on to the large section as well to help keep any of the differential shrinking/settling problems to a minimum.

Any further advice would depend on the design of the rest of the structure, especially the beam where the two decks meet.

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2  
Yes. Imagine setting out a table with chairs around it. This step severely limits the places that could work, and how big the table could be. – Jay Bazuzi Feb 14 at 1:32
Considering OP has gone to the trouble of making at least two complex 3D models of his deck design, I'm going to go out on a limb and suggest that he may already have considered what this deck will be used for and whether or not a step is appropriate. He also mentions that this is an addition to an existing deck, which isn't shown. For what it's worth, I think breaking up a flat deck with a step like this can make it look much nicer. – Mike Powell Feb 14 at 4:22
sketchup models like that take only a few minutes to produce, But, yes I agree that he is likely set on the multi-level design. I always try to convince my clients out of a multi-level design but have rarely succeeded. I still feel the need to put it out there. Generally, two 100 s.f. decks have way less functional space than one 200 s.f. deck. You can visually break up large decks by using different decking patterns, borders and colours with beautiful results. – decker Feb 14 at 6:02
up vote 2 down vote

For the second option, why don't you just build the two diagonal corners instead of that whole bat-ears shape? Seems like that would be the easiest of them all.

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big "d-uh" moment here. while focusing on whether option 1 or 2 is better, we blindly miss the obvious but unmentioned option 3! – decker Feb 13 at 20:07

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