Deck or Shed Foundation On Slope

[flyingvan]

   I used to supplement my pay by building decks and sheds for other firemen.  I wouldn't use this for a living quarters, but this is one way to get a perfectly square and level smaller foundation every time.

   You build the floor framing first, (I used 2x8's typically) building it from the inside out.  Every 4' there is a 3 1/2 inch slot formed, then a rim joist holds it all together. 
   Nail it all together on a flat surface somewhere, and square it up by measuring the diagonals.  Screw in a temporary diagonal brace to hold its shape.
   With help, carry it over to the building site.  Just sort of block it up somewhere close to level with scrap wood, rocks, whatever.
   Using the frame itself as a template, rough mark where each pier strap will go.  I just rammed my digging bar down in each corner and the middles of the 3 1/2" slot.
    Get the frame out of the way, and dig the footing for each pier strap.  Dig down to undisturbed soil and set the piers in concrete---I always use a minimum of 200# for each.  Don't worry about getting them set in the perfect spot, but make sure all the pier straps are oriented to be perpendicular to those 3 1/2" slots.
     After the concrete sets, carry the frame back over and position it over your piers.  Cut sections of 4x4's, pound them down through the 3 1/2" slot and between the metal pier straps.  Since you've positioned your straps perpendicular to the slot, the 4x4's are free to move a few inches in any direction---sliding between the straps one dimension, and sliding in the slot the other. 
      Now block up the frame again, and level the whole darned thing at once.  Make sure all your 4x's are seated on top of the piers and plumb, then run carraige bolts through them---through the holes in the pier straps, and through the frame itself.  (you can throw a few nails in first just to hold it all together if you want) It's good to end up with the 4x4's under the sole plate of your frame for weight transfer.  If your slope is such that you have some pretty tall 4x's, add diagonal bracing tying them together.  Your subfloor will keep it square while you frame.


        This deck was built like this 10 years ago as a 'temporary' structure.  Still rock solid.  I should have painted it.

     

[Backyardigan]

Well, I didn't build the framing first ...  I had stakes with copper wires running everywhere to try to get it all square--even figured out the square root of 2.  Then, with half the holes off by almost a foot, I finally realised I could just lay down my plywood sheets to square it, duh ....  Live and learn.

[OlJarhead]

I hate to say it but that sounds like too much work to me.  I simply measure out the area, dig my footings, drop in the piers, square the piers, build the deck on top of the piers and back fill.

No need to build the floor and then move it.

After many years my deck is still where it was built and still in good shape though I need to stain it again