How To Build a Deck Over a Concrete Patio

Determine the deck layout

The layout of your deck 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 in this project, you’ll need doubled sleepers to support any boards that run perpendicular to the others. We also installed sleepers to support the steps we later added to the concrete stoop.

For a standard decking design:

• From the top center of the deck, use a pencil and tape measure to mark the layout of the first sleeper on the concrete. Start a 1/2 inch from the house’s foundation or concrete edge.
• Continue measuring and marking from the first sleeper. Use standard joist spacing of 16 inches on center (o.c.) until reaching the end of the patio.
• Repeat this process on the left and right sides of the patio, 1 foot from the patio edge.
• Next, measure and mark 1-1/2 inches to the right of the 16 o.c. marks.
• Use a level or straightedge to draw a line connecting these three new parallel marks.
• Each sleeper edge will be positioned next to these lines.

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Cut and install spacers (optional)

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. While optional, spacers let you run sleepers parallel to the house, so decking can run perpendicular to the house (if that’s what you prefer). Otherwise, sleepers parallel to the house will block water runoff.

Spacers also allow sleepers to dry, preventing rot. “As long as the sleepers are following the pitch of the slab, you don’t need spacers. But if you want that as extra insurance it doesn’t hurt,” Collinsgru says.

• Measure, mark and rip the PVC board into 3 1/2-in. strips using a table saw or circular saw. This is the width of the sleepers.
• Mark and cut each strip into 2-in. sections with a miter saw. These will be your spacers.

Position 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.

Our project’s biggest time factor was the patio surface’s unevenness. 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).

• Lay a straight board across the patio in a few spots.
• Look for the highest hump in the patio and plan to position your first sleeper there.
• If using spacers, space them every 18 inches along the sleeper edge line marked on the patio.
• Lay the sleeper board onto the spacers or directly onto concrete if not using spacers.
• Work outward from the high spot, adding spacers and sleepers.
• Check for flatness along each sleeper and across them using a 4-ft. level.
• Add plastic shims to raise low spots.

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Predrill for concrete screws

All surfaces must be predrilled before securing with concrete screws.

• Position the 3/16-in. masonry drill bit over the center of a sleeper and spacer.
• Drill through sleepers, spacers and into the concrete with a hammer drill.
• Pull the bit completely out of the hole once or twice while drilling each hole to clear the dust. As you drill, dust compresses around the drill bit. That slows you down, strains your drill and overheats the bit.
• Drill the holes 1/4- to 1/2-inch deeper than the screw will reach. Extra-depth provides a space for dust and grit, so screws are easier to drive.

Pro-tip: 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.

Screw down sleepers

With holes predrilled, secure sleepers to the concrete.

• Use a drill with a driver bit to drive in concrete screws. Overhang the sleepers along one edge of the patio and trim them to exact length later.
• Screws should penetrate the concrete by at least one inch, 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.

Set sleepers in plane

When all the sleepers are screwed down, take a few minutes to double-check for flatness.

• Set a 4-ft. level on each sleeper, both across it and along it.
• If you find spots that are 1/16-inch or more out-of-plane, back out the screw and add or remove shims.

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Install flashing on sleepers

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.

“Flashing tape is very beneficial,” Collinsgru says. “It’s a cheap insurance to ensure water is not sitting trapped on your sleepers causing rot.”

• Lay flashing tape along the top of a sleeper board.
• Apply firm pressure to adhere the tape to the surface.
• Use scissors or a utility knife to cut it to length.
• Repeat this process across remaining sleepers.

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Plan decking layout

To avoid a half board or less at one end of the deck, check the layout first before securing. If necessary, cut end boards on each side of the deck floor for a more uniform look.

If using dried pressure treated wood, space decking boards 1/8-inch apart. If the wood is not dried, butt the boards tightly against each other, as they will shrink when dry. For composite boards, follow the manufacturer’s spacing recommendations.

• Lay deck boards in place across the sleepers.
• Make adjustments or cut end boards as necessary with a circular or miter saw.

Install decking boards

Installing deck boards over sleepers is just like installing them over standard deck framing. “Make sure you are using fasteners that are not too long,” Collinsgru says. “You don’t want them to hit the concrete.”

• Use deck screws to fasten deck boards to the sleepers with a drill and driver bit.
• Secure each board with two screws at each sleeper. “Always use screws, because nails back up over time,” Ricalde says.

Install a fascia board

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

• Measure the space between the bottom of the decking and the concrete.
• Transfer this measurement to a 1/2-in. PVC board.
• Rip the board to width using a table saw or circular saw.
• Fasten the fascia board to the sleepers using deck screws.

FAQs

What’s the difference between decking and wood?

Composite decking lasts longer and requires less maintenance than wood decking.

Should I use composite decking over my concrete patio?

If your budget can cover the added cost of composite decking, it can be an excellent choice over wood. “Composite boards are nice to use, but they’re expensive,” Ricalde says.

About the Experts

• Paul Ricalde has over thirty years of experience in the construction industry. He also provides in-depth home improvement videos on his YouTube channel, Paul’s Toolbox with over 360,000 subscribers.

• Sean Collinsgru is the owner of Premier Outdoor Living, an outdoor living space design-build firm in Southern New Jersey. Mr. Collinsgru is a Deckorators Certified Pro-elite, and specializes in unique decks, patios and landscaping.