Expert: Bruce E. Johnson - 10/23/2009

Question
Hello Bruce,
We are currently getting estimates to have a new 12'x28' deck built onto an existing, 8 year old concrete patio that was, for some reason, poured in two sections #3'x12' and 10'x12'#, separated by an expansion space.  The patio slopes gently for drainage along the house.  There is a door leading out to the patio with a brick edge step down depth #about 2 1/2" plus door frame thickness).
One contractor says door height should not be a problem using cedar but the other contractor wonders if it will be enough so that the door will not impact with the cedar decking.
Also, we live in Texas, very hot, very humid and the deck would be in very intense direct sun most of the year along with short, very frigid winters.  The soil/ground cracks easily here.

My questions are: 1)Would there be a problem using cedar boards with door height even with "sleepers" or shims as recommended by the contractors?  2)What would be the best way to allow circulation under the deck being so close to the patio?  3)Is deck weight a concern, or could it cause cracking of the concrete in case the ground makes the deck shift?  4)One guy wants to anchor the runners to the concrete with posts buried in the ground, the other guy wants to "float" the deck runners with posts buried in the ground. Which would you recommend?

Any advice would be appreciated!  Thank you!
Mary

Answer
Hi mary, I don't see any reason to worry about deck "circulation" in your case.  First of all you would want your sleepers to run with the slope of the deck so that water will drain as the original slab was designed for.  A 1x4 sleeper tapconned to the patio is 3/4" thick, plus the cedar decking thickness of 1 5/8" should allow for the door to swing over it if you have a 2 1/2" step down. Secondly I would use pressure treated wood for the sleepers instead of cedar and then use the cedar for the decking.  I don't see a weight problem using the existing concrete for bearing, it is done all the time with reasonable results..I'm not sure what your contractors are talking about with the posts buried in the ground and one "anchors" and one "floats"..Both seem to be talking about the same thing since both are burying posts in the ground and attaching the deck to them..Definitely you can anchor to the concrete slab where possible, obviously you will have to support the part of the deck extending over the concrete patio by either pouring concrete stip footings, using pressure treated wood pilings buried in the ground to support carrier beams, or using precast footing blocks embedded in the ground to support carrier beams which in turn support your deck framing..I hope this information helps, please feel free to write again regarding this or other matters, sincerely bruce e johnson..bejohnsonconsulting.com