How to Build a Deck Over a Concrete Patio

The ultimate solution for a hopeless slab

Is your old concrete patio an eyesore? You can avoid the cost and mess of tearing it out by just screwing down wood sleepers and decking over it.

By the DIY experts of The Family Handyman Magazine

TIME

Multi-day

COMPLEXITY

Moderate

COST

Varies

Before!

This was the ultimate bad patio: severely cracked and cratered, some areas raised by frost, others sunken after 50 years of settling. Originally, it was tiled, then the tile was chiseled off and the pockmarked surface got a coat
of paint.

A slab with this much damage can't be fixed. But it can be covered up—and this article will show you how. The results look just like a deck, but getting them is much easier and less expensive than building a deck from scratch. In most cases, this project is also less expensive than a new patio installed by a contractor. Local contractors estimated costs of $7 to $10 per sq. ft. to remove this patio and pour a new slab. You could probably replace your patio yourself for less than the cost of this project, but DIY demolition and concrete pours are big, backbreaking jobs.

Will It Work On Your Patio?

Even if your patio is in terrible shape, you can deck over it. Cracks, craters and seasonal movement along cracks are no problem. But beware of these three situations:

  • If an area is badly cracked and sinks noticeably year after year, any decking you put over it will also sink and develop a low spot. In most cases, settling concrete stops sinking eventually, so delay this project until it does.
  • This project raises the level of your patio by 2-1/2 to 3-1/2 in. (depending on the thickness of your decking and whether or not you put spacers under the sleepers). So any door thresholds adjoining the patio must be at least that far above the concrete. If not, this project won't work for you. If you live in a climate where the ground freezes, allow an extra 1/2 in. so that seasonal “frost heave” can raise the slab without damaging the threshold.
  • Stairs connected to the patio can complicate this project. To keep step heights equal, you'll have to raise the treads by the same distance you raise the patio (2-1/2 to 3-1/2 in.). On concrete steps, that's a straightforward job: You can treat them just like the patio, screwing sleepers to the treads and risers and decking over them.

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Time, money and tools

Covering a patio with decking typically takes a weekend or two. This patio took much more time—five long days. That's partly because it's a big one (14 x 28 ft.). The grid pattern formed with different-colored decking also added a few hours to the job. But the biggest time factor was the unevenness of the patio surface. All those ridges and sunken spots meant hours of tedious shimming under the sleepers to form a flat surface for the
decking (see Photo 3).

The cost of this project depends mostly on the decking you choose. Decking ranges from about $1.50 per sq. ft. for treated wood to more than $10 per sq. ft. for a top-grade manufactured product. The other materials for this project add up to about $1.50 per sq. ft., so your total cost could be anywhere from $3 to $12 per sq. ft. For looks and durability, we used two different colors of decking made from PVC, but there are less expensive alternatives.

Aside from standard carpentry tools, you'll need a hammer drill for this project. You can get a hammer drill for less than $50 that will do the job. But consider spending $100 or more. Even a very small patio will require more than 50 holes, and a more powerful drill will make that chore a lot easier. Also consider buying an impact driver. Impact drivers pack a lot more torque than standard drills or drivers and will drive concrete screws much better. Most models are cordless, but you can still find inexpensive corded models online.

Figure A: Deck Over a Patio

Sleepers screwed to the concrete allow you to screw on decking. Spacers and flashing tape protect sleepers from moisture and rot. Fascia boards hide exposed edges for a neater look.

For a, printable version of Figure A, see Additional Information, below.

This cutaway shows how to build a deck over a concrete patio. Figure A: Deck over a patio
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Plan the layout

The layout of your sleepers will depend on the layout of your decking. If you want a standard decking design—all the deck boards running one direction—all you need are rows of parallel sleepers. If you want a more complicated decking pattern, like the one shown here, you'll need doubled sleepers to support any boards that run perpendicular to the others (see Figure A). We also installed sleepers to support the steps we later added to the concrete stoop (see Photo 1).

Solve Water Problems First

This corner of the patio had settled by more than 2 in. over the years. That meant a big reservoir after rain—and water in the basement. So we filled the reservoir with exterior-grade self-leveling compound. After the first batch hardened, we poured on a thin coat and gave it a slight slope so water would run away from the house.

Self-leveling compound hardens fast, so you can get on with the project. But it's also expensive. If you're not in a rush, you can get similar results for less than one-third the cost with concrete topping mix such as Sakrete Top 'n Bond or Quikrete Sand/Topping Mix.

We also took a couple of other water-fighting steps. To prevent water from seeping down along the foundation, we caulked the gap between the patio and the house. At the other end of the patio, a corner of the slab had sunk slightly below the level of the soil and rainwater pooled there. To correct that, we shaved off the sod with a spade, dug out a couple of inches of soil and replaced the sod.

Fix any water problems before you build a deck over a concrete patio. Water problem
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Lay the sleepers

The sleepers don't have to be level‐they can follow the slope of your patio. But they do need to form a flat plane. If your patio is in good shape, you'll get a flat plane automatically. If your patio has ridges and sunken areas, you'll spend lots of time fussing with shims.

To preview the situation, lay a straight board across the patio in a few spots. Look for the highest hump in the patio and fasten your first sleeper there. Then work outward from the high spot, adding sleepers and checking for flatness along each sleeper and across them. Add shims to raise low spots.

Screwing down sleepers with concrete screws (Photo 2) is simple, but there are some things to keep in mind:

  • Screws should penetrate the concrete by at least 1 in., so 3-1/4-in. screws are perfect. In low spots, where we had to stack up shims, we switched to 3-3/4- in. screws.
  • As you drill, dust compresses around the drill bit. That slows you down, strains your drill and overheats the bit. To clear the dust, pull the bit completely out of the hole once or twice while drilling each hole.
  • Drill the holes 1/4 to 1/2 in. deeper than the screw will reach. Extra depth provides a space for dust and grit, so screws are easier to drive.
  • Have extra drill bits on hand. As a bit wears, it doesn't just drill more slowly; it also bores a slightly smaller hole and screws become harder to drive. We replaced each bit after about 40 holes. When all the sleepers are screwed down, take a few minutes to double-check for flatness. Set a 4-ft. straightedge on each sleeper, both across it and along it. If you find spots that are 1/16 in. or more out-of-plane, back out the screw and add or remove shims (Photo 3).

Why Use Spacers?

You could lay your sleepers directly on the concrete, but we bought a 1/2-in.- thick PVC trim board and cut spacer blocks from it. Here's why:

  • Spacers let you run sleepers parallel to the house so decking can run perpendicular to the house (if that's what you prefer). A patio typically slopes away from the house so that water runs off. If you run sleepers parallel to the house and set them directly on the concrete, each sleeper will block runoff. But with spacers, water can run under the sleepers.
  • Spacers allow for longer decking screws. We wanted to use Cortex screws, which come with cover plugs made from the same material as the decking. They're easy to use and almost invisible. But they're 2-3/4 in. long; that's too long to sink into our decking if we use sleepers only.
  • Spacers let the sleepers dry out. If kept damp, common grades of treated wood will eventually rot. Spacers keep the sleepers off the damp concrete so they can dry.

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Install the decking

Before decking, we covered the sleepers with flashing tape. Without it, water soaks the tops of the sleepers and the decking prevents the wood from drying. Common grades of treated lumber will rot if kept permanently damp, and flashing tape is the best insurance against that.

Installing deck boards over sleepers is just like installing them over standard deck framing (Photo 4). We began with the darker “accent” boards, screwing them into place temporarily to act as guides for the “field” boards. When we reached the end of the deck, we removed the center divider board and cut it to final length. Then we removed and mitered the border boards and trimmed the sleepers to final length.

To cover the ends of the sleepers, we used a deck “fascia” board made from 1/2-in.-thick PVC. We cut the fascia into strips and screwed them to the sleepers.

Materials List

Aside from the decking, here's an estimate of what you'll need to cover 100 sq. ft. of patio. Exact quantities depend on the shape of your patio and the layout of the decking.

  • 90 linear ft. of treated 2x4
  • 90 linear ft. of flashing tape
  • Sixty 3/16” x 3-1/4” concrete screws
  • 1/2”-thick PVC trim or deck fascia (for spacers), plastic shims, 3/16-in. masonry drill bits (minimum drilling depth of 3-1/2 in.)

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Keeping it simple

If you're a beginning DIYer, don't let all the details on our deck scare you away. Your project can be a whole lot easier if you choose a simple decking design like the one at right. With all the deck boards running in the same direction, all you need are sleepers centered 16 in. apart. You won't need to do the careful measuring required by our design, or make angled miters and other fussy cuts. A simple deck design makes this project almost impossible to get wrong. If you have a badly uneven patio like ours, flattening the sleepers with shims (Photo 3) may take hours. It's tedious but not complicated.

You can slash the cost by using treated wood deck boards instead of manufactured decking. And if you live in a drier climate where the sleepers won't stay damp, you can skip the spacers and flashing tape.

More Ways to Improve a Patio

Whether your patio is in bad shape or just bland, there are many ways to revive it. But before you weigh the options shown below, there's one thing to consider…

The crack factor Cracks in your patio drastically limit your options. That's because cracks tend to move. Some grow wider over time, while others shrink and widen as the soil freezes and thaws. Some become uneven as one side of the crack sinks. Any movement happens so slowly that it's hard to detect. But if you know—or even think—that you have moving cracks, you have to choose a patio upgrade that can “float” over moving cracks without becoming damaged.

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More cover-ups for a cracked patio

Along with the deck project shown on the previous pages, here are some other projects that can withstand moving cracks:

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Projects for a crack-free patio

If your patio isn't cracked, you could choose any of the options above or either stain, tile or resurface the concrete.

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Required Tools for this Project

Have the necessary tools for this DIY project lined up before you start—you’ll save time and frustration.

  • Miter saw
  • Circular saw
  • Drill/driver, cordless
  • Level
  • Hammer drill

Required Materials for this Project

Avoid last-minute shopping trips by having all your materials ready ahead of time. Here's a list.

  • Treated 2x4s
  • Self-leveling compound
  • Flashing tape
  • 3/16 x 3 1/4-in. concrete screws
  • 1/2-in. thick PVC trim
  • Plastic shims
  • Decking