Yes, you can build a deck over concrete, and the three practical routes are sleepers laid on the slab, adjustable pedestals, or an independent framed deck. Which one fits depends on slab condition, door threshold height, and whether the deck attaches to the house, which can trigger a permit. Before buying lumber, run a plastic sheet moisture test and measure your thresholds. Ask your building department which IRC deck provisions apply locally.
TL;DR:
- Tape plastic to the slab for 24 hours; condensation signals moisture risk, while cracks, shifting sections, or pooling should be addressed before framing.
- Local rules vary, but permits commonly apply above 300 square feet, over 30 inches above grade, or when decks attach to houses or serve required exits.
- Sleepers cost less but raise the surface and need spacers, flashing tape, and drainage gaps; pedestals level stable uneven slabs, while posts suit weak slabs.
- A concrete ledger needs approved 1/2 inch expansion anchors, specified embedment and spacing, and flashing; an independent post and beam frame avoids ledger attachment.
- DIY suits sound slabs and modest height increases if you know carpentry; hire a pro for tight thresholds, structural attachment, or complex drainage.
Table of Contents
- What should you check on the slab before building?
- When do you need a permit for a deck over concrete?
- Which framing method suits your slab?
- How do you keep moisture and water from rotting the frame?
- How do you anchor to concrete or build free-standing?
- What does a sleeper-style build look like, step by step?
- When should you do it yourself, and when should you call a pro?
- Ready to turn your concrete patio into a deck?
- FAQ
- Sources
What should you check on the slab before building?
A slab can carry a deck only if it is basically sound. Walk it with a tape measure, a level, and your phone camera, and look for these problems:
- Wide structural cracks, crumbling spalls, or one section sitting higher or lower than its neighbor. Heave and settlement like this often mean repair or removal comes first.
- Trapped moisture. Tape a square of plastic to the slab for 24 hours, then look for condensation underneath. Moisture wicking from concrete is a primary cause of framing rot, so a wet result changes your materials and details.
- Pitch and pooling. A slab that drains toward the house or holds standing water needs fixing before any deck goes on top. Drainage fixes for patio pooling are worth reading while you plan.
- Door thresholds. A sleeper deck raises your walking surface, according to Family Handyman’s patio deck guide, which can crowd door clearances and change stair riser heights.
If anything looks doubtful, photograph it, write down dimensions, and bring both to a contractor or your local building department.
When do you need a permit for a deck over concrete?
Rules vary by city, so treat this as a checklist of common triggers rather than a guarantee. Permits are commonly required when a deck is over about 300 square feet, when the walking surface sits more than 30 inches above grade, when it attaches to the house, or when it serves a required exit door.
- IRC Section R507 is the code section that covers decks, including ledger attachment to concrete walls, hold-downs, and a free-standing option that avoids attaching to a foundation wall. You can read the prescriptive text in the IRC deck provisions.
- If you plan a ledger on concrete, inspectors look for the right anchor type, embedment, and flashing that keeps water out of the connection.
- Bring slab photos, your planned footprint, and your target finished height to the permit counter, or have a contractor prepare the drawings.
Our own walkthrough of deck permit requirements goes deeper on what to gather before you apply.
Which framing method suits your slab?
Each method solves a different problem, so match the choice to what your slab and doors demand.
- Sleepers on the slab. Pressure-treated 2x lumber is fastened to the concrete with concrete screws, flashed, and spaced so water can drain. It costs less, goes faster, and hides rough concrete. The trade-off is added height and careful moisture details.
- Adjustable pedestals. Plastic or composite supports create a ventilated gap and make leveling easy on an uneven but stable slab. The finished height stays consistent across the whole surface.
- Independent framed deck. Posts, beams, and footings give you structural separation from the slab. This is the route when you must match a door threshold exactly or when the slab could not be trusted to carry loads. A free-standing beam next to the house, as allowed under IRC R507.10, avoids a ledger altogether.
Run through the same selection checklist each time: slab condition, finished height and transitions, budget, long-term upkeep, and whether your local code accepts a ledger attachment.
Pro Tip: Measure from the top of the slab to the underside of each door threshold first. If the available height is tight, sleepers may not fit, and a low-profile pedestal system or a framed deck may be a better plan.
How do you keep moisture and water from rotting the frame?
Trapped water is the enemy of any deck built against concrete, and the fixes are simple and cheap.
- Repeat the plastic sheet test in a couple of spots, especially low areas. Condensation under the plastic means wood in direct contact with the slab is at higher risk.
- Place spacer blocks between each sleeper and the slab. Family Handyman recommends cutting them from PVC trim and setting them between sleepers to help keep the wood from sitting in pooled water.
- Cover the tops of the sleepers with flashing tape before decking goes down, which stops water from soaking in through the screw holes.
- In damp or shaded spots, composite or PVC boards cut maintenance, though drainage and airflow still matter. Our breakdown of composite decking cost helps you weigh the price difference.
Pro Tip: Do not seal the edges of the deck tight against the house or the slab. A visible gap and open airflow let the underside dry out after rain.
How do you anchor to concrete or build free-standing?
Tying a deck to concrete takes the right hardware. Under the code language in the IRC public comment text, a ledger attached to concrete uses approved 1/2-inch expansion anchors installed to the spacing and embedment rules, and you should follow the manufacturer’s instructions as well.
- Tension hold-down devices are described in the American Wood Council’s DCA 6 deck guide, and an engineered alternative is allowed when it is documented.
- If a ledger is impractical or you simply want to skip it, a free-standing beam and post system beside the wall is the prescriptive alternative.
- For sleepers, use a hammer drill with a masonry bit and drill slightly deeper than the screw length so dust has somewhere to go. Choose concrete screws with an embedment suitable for the slab and follow the manufacturer’s instructions.
- Flash every ledger connection so water cannot track behind it.
What does a sleeper-style build look like, step by step?
Use this sequence to plan your own project or to check a contractor’s quote.
- Prepare. Sweep and wash the slab, run the 24-hour moisture test, record every door threshold, and fix trip hazards or pooling spots.
- Lay out. Find the slab’s high point, set straight boards to align your sleepers, and place spacers between the sleepers and the slab. Check that the tops of the sleepers form one flat plane.
- Fasten. Predrill through sleeper and spacer with a masonry bit, go slightly deeper than your screw length, then drive concrete screws to the embedment specified by the manufacturer.
- Protect. Cover each sleeper with flashing tape before any board goes on.
- Deck. Install boards with exterior-grade deck screws, as specified by the deck plan and fastener manufacturer, keeping gaps for drainage.
- Finish. Add fascia or trim for a clean edge, then confirm the transitions at doors and stairs are safe and consistent.
The tools are modest: a hammer drill, a level, a circular saw, a driver, and masonry bits. Most of the labor is in layout, so take your time there.
When should you do it yourself, and when should you call a pro?
Our view is simple. DIY makes sense when the slab is sound, the height increase is modest, and you are comfortable with carpentry. It stops making sense when thresholds are tight, the deck must attach structurally to the house, or drainage problems are tangled up with the slab.
We run consult-to-build projects with our own in-house crews, warranty-backed installations, and experience with composite, PVC, and cedar. If you decide to hire out, bring slab photos, measurements, your target finished height, and any known permit constraints. Our guide on how to choose a deck contractor shows what to verify and why to collect several bids. If you are still deciding between a deck and simply keeping the patio, this comparison lays out the trade-offs.
— Vlad
Ready to turn your concrete patio into a deck?
We handle the slab assessment, permit paperwork, and build under one roof, so you are not coordinating trades yourself. Relevant services include:
- new deck installation service with our in-house crew
- Custom deck installation tailored to your thresholds and layout
- Deck replacement when removing and rebuilding makes more sense
- Everett deck design service before any lumber is ordered
For a consultation, have slab photos, dimensions, your preferred decking material, and notes on door heights ready. Start on our new deck installation service and tell us what you have.
FAQ
Can you put decking directly onto concrete?
Not directly. Boards need support and airflow, so they sit on sleepers, pedestals, or a framed substructure instead. Skipping that gap traps moisture, which is the main cause of rot in deck-over-concrete builds.
Is it possible to lay decking boards directly on concrete?
Technically yes, but it is a poor idea. Boards laid flat on a slab cannot drain or dry, and they tend to cup, stain, and decay early. A sleeper system with spacers and flashing tape gives water a path out.
What is the cheapest way to cover a concrete patio?
A sleeper deck is usually the lowest-cost route because it uses common lumber and concrete screws. It does raise the walking surface, so check your door clearances first.
How do you test a slab for moisture before building?
Tape a square of plastic to the concrete for 24 hours. Condensation underneath means moisture is moving up through the slab and you should plan for drainage gaps and moisture-tolerant materials.
