I used TimberTech 5/4 product over my concrete slab.

I used 1 1/2 sleeper system and attached the 5/4 product to that. The product was just over an 1"

So you would be fine with the clearance you stated 6".

Hey, thanks for the help, but I'm not familiar with some of this...

What is " 1 1/2 sleeper system"? It sounds like a support layer under the decking itself... Is this right?

My main concern was the gluing of composite to concrete-- would I have to prep the concrete at all, etc. The guy at the local orange big box said I could use construction adhesive (decking direct to concrete) but it would start to come loose in 5-6 years....

Texas Boy

For composite decking, you should use screws 2 1/2"(stainless steel). the sleeper system should be made with:

treated lumber 2x4 or 1/4 make a frame using 2x4's or 1/4 as joist spans should be no more than 16" and attach TimberTech 5/4 to it. I would recommend doubling up the butt joints for added fastening support. When you are attaching the product, make sure you space the planks 1/8" side to side and at the butt joints.

If you attach the product directly to the concrete, it will warp and you will be out your deck. I hope this helps.

Thanks,

The deck guy