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Installation & Maintenance

How to Install a Composite Deck Over Concrete

October 10 2019
composite decking concrete
How to Install a Composite Deck Over Concrete - Header Image

Tired of looking out over a concrete jungle in your own backyard? Upgrade your view by installing a natural-looking capped composite deck over concrete.

When you picture your perfect backyard, you probably think about things like meticulously maintained landscaping, a spacious in-ground pool (maybe with an adjoining hot tub), and plenty of room for your kids and pets to play. One piece that probably never enters your mind - the concrete slab jutting out from the back of your house.

Listen, we’re not saying there’s anything wrong with concrete – it’s an incredibly functional material. But this is your backyard, not the Hoover Dam. To get an outdoor living space you can really be proud of, you need something that’s both functional and aesthetically pleasing. Enter capped composite decking - the perfect material to upgrade your space by adding a gorgeous deck over concrete structures. 

If you have a concrete patio you want to transform into a more beautiful and impactful outdoor space, capped composite is not only a great choice, but it’s pretty easy to pull off. In this guide, we’ll provide you with basic instructions to help install a composite deck over concrete.

Step #1: Set up a Sleeper System

To install a composite deck over concrete, you’re going to need a sleeper system. A sleeper system is a substructure made up of joists that sits on the surface of the concrete below the decking. The space between the concrete and the decking material is essential because it allows for air circulation and water drainage to occur, thus protecting the capped composite deck boards from the risk of excessive moisture-related damage.

Another benefit of a sleeper system is that it makes it easier to clear out any accumulated debris from under the deck. Of course, before you begin installing a deck over concrete, you should always check with your local zoning commission to find out if there are any special building codes you need to follow.

Before Installing a Sleeper System

Here's what you need to consider before building your sleeper system:

  • Solve any water run-off or pooling problems on the patio before starting.
  • Depending on the condition of your concrete structure, you may need to level the surface before setting up your sleeper system. 
  • Mark the sleeper locations on the patio before you start drilling (remember to note the extra sleepers if you’re adding stairs or railings to the deck area).
  • Pre-drill holes for your concrete screws.
  • Sleepers need to be at least 1-1/2 inches in both height and width.
  • Sleeper systems should never be installed on gravel, sand, dirt, or on concrete pavers (although spacers are permitted for improved drainage).
  • Choose sleepers that are resistant to wet conditions and rot, especially if harsh weather conditions are a factor in your area.
  • Install the sleepers directly on the concrete and make sure the screws penetrate the surface by at least one inch.
  • Install the sleeper joists parallel to the direction of the water run-off.
  • Space the joists according to standard space codes (no greater than 16 inches on center).

Step No. 2: Protect the Sleeper System

With your sleeper system installed, you should now cover the sleepers with flashing tape. This is not a mandatory practice, but the flashing tape helps protect the tops of your sleepers from absorbing water. This step takes on greater importance if you’re using common grade lumber, as it will rot rather quickly if it remains damp.

Step No. 3: Install the Composite Deck Over Concrete

Next, you can install your capped composite deck over concrete like you would if were installing the boards on a traditional deck. (You can visit our installation page for detailed instructions on TimberTech decking lines.) Here are a few important things to consider based on which type of composite decking and design you choose.

TimberTech Specialty Deck Lines

It’s important to note that the surfaces on some TimberTech boards (e.g., ReliaBoard) are directional in manner. A notch has been added to one side of the boards so you can better identify the proper direction. When installing, the notched edge needs to be laid to the same side throughout the entire installation for a consistent appearance.

Fascia and Riser Boards

TimberTech’s Fascia and Riser boards are also directional in manner and have one long beveled edge on the front and back. With these two board types, the beveled edge needs to be laid to the same side throughout the installation to ensure a consistent appearance. This is important to remember if you rip a piece. Note the location of the bevel before you rip, so you don’t accidentally install the board facing in the wrong direction.

Installing a Multi-Color Deck Over Concrete

If you’re installing two different colors of boards for your deck, then you can screw the accent color boards into place temporarily to act as guides for the primary color boards. To cover the ends of the sleepers, install deck fascia board.

Ready to Upgrade Your Backyard?

Find a contractor near you to learn more about installing a TimberTech® composite deck over concrete structures.