There are plenty of online and book solutions for covering your concrete slab, but none seemed to describe how to do the same with an elevated slab. Many of my ideas and technical advice came from The Family Handyman and I encourage you to see specifics there. So, I decided to take the best from several sites and create a customized solution for people who want to cover their concrete that happens to sit on 4 feet of above ground cinder block. Here’s how I did it:
I have a Home Depot less than 5 miles from my house which is why I list HD supplies. I’m sure you can find materials comparable to the ones I have here at your local hardware.
Floating deck instructions (always confer with your local government about building codes and permits!).
1. Prep your concrete. Make sure your old concrete is clean, clear of paint, level and flat. If it isn’t level, apply a coat of exterior concrete leveler and let it cure for several days. Doing this will allow your thin support wood to lay flat and avoid bowing deck boards. It will also prevent standing water on your deck. This Old House does a nice job of explaining how to do this for a garage and works for this case.
2. Measure for deck boards. Once your leveler is cured, measure out the portion of the concrete slab that you want to deck, if not all. You will need enough deck boards to run flush with your concrete slab. Keep in mind there may be cutting needed and lumber from the store is usually short a quarter inch on most dimensions (allows lumber mills the ability to cut and put out more product quickly.) If you have stairs going up to your slab, I recommend 1 5/32 inch boards as it is not as noticeable when you move from one step to the next.
3. Low Profile Sleepers. Using well painted, flat 1X4 furring strips as your sleepers, apply a good layer of Liquid Nails to the bottom side of your sleeper. The gap between your sleepers should not be more than 16 inches. Because I have steps, my sleepers needed a low profile which is why I laid mine with the 4 inch side down. Press down and hold for a few minutes so the adhesive spreads and grabs.
Drill holes in the sleepers with a masonry bit until you penetrate the concrete slab. Make sure you read the depth specifications for your mason screws as most have minimum requirements. Some mason screws like Tapcon come with mason bits. If you are using a standard drill, use the rotary bits, not the hammer bits as it will not work properly. Screw in the boards for that extra layer of strength.
4. Close Sleeper Gaps. Box in your sleepers to avoid animals, debris and dirt from getting underneath your deck. I used 1X4 furring strips to fill in the gaps.
5. Place Deck boards. Place your cut deck boards on top of your sleepers, make them flush with your slab and screw them in using weather resistant screws. The goal with these screws is to hold the deck boards to your sleepers, not go through the concrete. Measure the depth needed to get most of the way through both boards.
If you plan on staggering your deck boards, check to see if you need to add another sleeper to catch the end of the staggered board to avoid the board warping or cracking. It is especially important to add the extra sleeper if this is a high traffic area of the deck (i.e. the front door to your house).
6. Framing your deck. Measure the bottom of your concrete slab to the top of your deck board for your frame. I needed a 1X8 deck board. Cut a 45-degree mitre on each end for a clean box end. Use construction adhesive and mason screws/anchors to hold the board into place.