I am building a deck and have questions

[dauffenbachkevin]

I am planning on building a deck for my parents over an existing concrete patio.  I know how to do the framing etc.  I just have a couple questions on what materials to use.  The patio is roughly 20' x 12' and will only sit about 1' above the concrete slab.  The deck will sit in a corner of the house so two sides will butt up to the house/garage and the other two are open.  I was first thinking of making a free standing deck but stabilizing it better by extending the deck past the edge of the slab and pouring 4' deep column footings for the 4" x 4" posts to be fastened to.  These footings will run on the 2 sides that are not butt up against the house.  On the 2 sides that do butt up against the house I was going to fasten the posts directly to the concrete slab (I know probably a bad idea but I think it will be fine with 2 of the sides being supported by 4' deep footings).  The only reason I wanted to go freestanding is because the deck is so low to the ground that if I did a ledger against the house I would have to attach it to a CMU foundation wall at the garage (which I dont feel comfortable doing)

I plan on using 2" x 10" for the joists and spacing them every 16"
I plan on spacing the footings and 4" x 4" posts every 4 - 5 feet

Attached is a link to my dropbox with  a sketch with post/footing layout.  Dashed lines are the joists and hatched are is the house/ garage

LINK: https://www.dropbox.com/s/is7czrr8nj15z8u/Deck%20Sketch.pdf

GIVE ME YOUR THOUGHTS PLEASE!!!!

[Redoverfarm]

Maybe I am missing something but why not just lay up concrete block on the poured patio for your piers.  As far as the load it will be very little difference than the way you are considering.  The height which you are trying to achieve will be difficult in that using 2X10 you already have 9-1/4", add the deck boards of 5/4" and you are already at 10-1/2" which doesn't leave a lot of base to rest your rim joist on.  Maybe a 4" solid block will work.

With very little elevation from the slab you might be better off to use a fabricated concrete deck block.  If you have half the deck resting on the slab and one end resting on poured piers/4X4 then any frost heave might be uneven whereas by resting the entire deck on the slab it might be more consistent from one end to the other.

[SouthernTier]

Haven't studied your sketch, but the way to build a deck is to follow this:

http://www.awc.org/publications/dca/dca6/dca6-09.pdf

[dauffenbachkevin]

@Redoverfarm

So I can fasten the posts directly to the concrete block or deck blocks with a galvanized post mounts?  That seems a lot easier and cheaper.  I can also fasten the 4" block to the existing slab as well.  If I put in more posts/block do you think I would be fine with using 2 x 8 's in lieu of 2x10's?  Maybe put cross bracing in with 2x8's just to be safe?

[Redoverfarm]

@Redoverfarm

So I can fasten the posts directly to the concrete block or deck blocks with a galvanized post mounts?  That seems a lot easier and cheaper.  I can also fasten the 4" block to the existing slab as well.  If I put in more posts/block do you think I would be fine with using 2 x 8 's in lieu of 2x10's?  Maybe put cross bracing in with 2x8's just to be safe?

The block can be mortared in place and later mounts can be bolted to the blocks using wedge bolts or similar. Prefabricated deck blocks are made to saddle the joist.  You would need to secure them to the slab with a bolt and then tapcon a strap to the joist.  Is has been awhile since I looked at the Simpson site but they may have an applicable mount to use in this application.   As far as the spacing and dimensional lumber for your span I would check a span chart.  I think there is one in the forum or use the search feature to find it. You might find is here  http://www.awc.org/pdf/wsdd/toc.pdf

My point being using dimensional lumber your support would be so short using 4X4 that there would be insufficient for attachment to the slab and the joist.  I am sure there is probably a solution that will work but it may take a little "out of the box" approach.  Of course there may be some code requirements in your area that would dictate the manner that you construct the deck.