how to attach a 3 season room to my cabin

[FrankInWI]

I have a "cabin" I built on a slab (no footing) that I would like to add a screen porch too.  We love the outdoors but in the summer you can be eaten by the mesquites.  The porch would be closed in, more like a 3 season room in Wisconsin.  (I bought the 1 ½ story plans, but built with trusses cause of approaching winter.)
I'm tempted to do piers like the plans I have and build the porch on top of them.  I would have posts and beam to hold up the back part of the porch adjoining the cabin instead of ledger board attached to cabin.  I am "connecting" to the house roof line only to keep the rain barrier constant but would not have it structurally relying on the cabin (most of the roof line I am connecting too is a faux roof edge on the first story of a gambrel roof building. 
The windowed/screened - porch/room would be across the front above.  the roof line under the dormer is just trim like, not structural. I'd take off that facia board and tuck the plywood porch roof sheets up against the sheets already on the building.

Do I have a problem with a 10 X 20 front porch solidly anchored to earth being somewhat joined to a cabin floating on 25 tandem dump loads of sand (to get above 100 year flood plan)?   
<a href="https://s82.photobucket.com/albums/j262/fauer/?action=view&current=Picture322.jpg" target="_blank"><img src="https://i82.photobucket.com/albums/j262/fauer/Picture322.jpg" border="0" alt="Photobucket"></a>

[FrankInWI]

Did I do something wrong?  Bad manners asking this here?  I'm I so far off base no one replies? 

thanks / confused

Frank

[rocking23nf]

If the cabin is floating, Its expected to shift correct?

If the extension is anchored, its not going to move.

So when one shifts, and the other doesnt, I could see some problems there.

But im not familiar with the type of foundation you have, because a cabin that size I would assume would have needed a anchored foundation.

[FrankInWI]

although it's in wisconsin (clay) it's in an area that is very sandy.  Took topsoil off and dumped more sand and some pit run at the top and put slab on top of that.  Permit says garage/storage but inspector knew upper was to be converted to residense when house would be built next to it.  He made no issue of slab as it was, many houses are just on slab like that here.  all that said....there is a continuous hairline crack on the floor somewhat parralell to one end.  If it stays hair line, I won't worry much. 

Because it is on slab... that is why I figure porch to stand on it's own, with roof line only co-joined.  I don't expect so much movement as to create an issue there.  (I think....)

[John Raabe]

Frank:

The slab probably had a thickened edge with rebar reinforcing did it not? (I see where you said no footing). At any rate your plan to support the screen room separately is a solid idea. My only question is will the floor levels work out and do you have enough height for the piers, beams, joists and decking? If you don't have plumbing and wiring you need to get at in the floor, then all the wood framing could be PT and set pretty low.

[FrankInWI]

thanks....it is thicker concrete around the perimiter.  I hope they did the right thing with the rebar.  I'll just have to keep my eye on that crack and stay nervous.  I probably should have spent a little more and had it done better yet. 
I was thinking not PT cause not in ground contact, but I can see where I should stop cutting corners too and will go pt. 
no plumbing, and electric coming out from boxes in existing house wall.  I don't expect height to be an issue, in fact I was worried it might require a step down.  Guess not.
thanks folks

[John Raabe]

Little hairline cracks in a slab are not a concern unless they start to open up. Then it could be settlement and not just stress contractions as it cured.

The general rule for PT lumber is anything closer than 6" to the soil needs to be treated. In termite and carpenter ant areas there can be good reason to do all exposed framing in PT.