Step-by-step instructions for installing a floating deck over concrete

Yes, you can build a floating deck on top of a concrete patio if the slab is sound and drains away from the house. Create a low, ventilated platform using sleepers on pads or adjustable pedestals with joists, then lay your decking (wood, composite, or PVC). Follow simple rules: keep joists 16" on center (12" if boards run on a diagonal), leave gaps for expansion and water, never anchor to the house, and protect the tops of sleepers with flashing tape. Maintain door and wall clearances, and don’t block water flow.

Read more: How to Design a deck layout for a small backyard (4m×6m) with steps and seating.

What “floating deck over concrete” really means

• Floating = freestanding. The deck does not connect to the house with a ledger. It sits on the slab using pads, spacers, or pedestals that raise and ventilate the frame.

• Good candidates: Ground-level patios; slabs that are stable, crack-free (or only hairline), and sloped away from the building (about ¼" per foot ≈ 2%).

• Poor candidates: Roof membranes or balconies (different systems and codes), slabs with standing water, doors with too little clearance, or concrete that’s heaved or crumbling.

Safety note: Local rules vary. Adding railings, steps, or lighting may require a permit. Check your city’s guidelines first.

Read more: What deck shape fits an L-shaped house?

Before you start: measure the “height stack”

You need enough height for every layer:

Concrete slab → pads/pedestals (¼"–2" typical) → sleepers/joists (1½" if 2× framing) → decking (¾"–1"+).

• Door thresholds: Aim for at least 1½–2" (38–50 mm) of clearance from the new deck surface to the bottom of the door.

• Walls/siding: Keep a ½" (12 mm) perimeter gap for expansion and airflow, and never cover weep screeds.

If you’re tight on height, choose low-profile pads + sleepers instead of taller pedestals, and consider thinner composite boards.

Read more:  modern deck ideas with low maintenance.

Choose your build system (pick one)

1. Sleepers + spacer pads (lowest height)
   
   

• Lay treated sleepers (2×4 or 2×6 on the flat) across the slab on rubber/HDPE pads spaced every 16–24".

• Pros: Thin build, simple tools, budget-friendly.

• Cons: Limited ability to level a wavy slab; best for slabs that already drain well.

2. Adjustable pedestals + joists (best levelling)
   
   

• Place adjustable pedestals on the slab, set height, then lay joists across them.

• Pros: Fine control, easy to keep the deck plane flat while preserving water flow beneath; great for uneven slabs.

• Cons: Costs more; adds height.

3. Deck tiles (fastest alternative)
   
   

• Interlocking wood/composite tiles on pads or small pedestals.

• Pros: Quick makeover, minimal tools.

• Cons: Limited design options; usually thinner and not ideal for complex edges or stairs.

Read more: Deck: wood vs composite vs stone—pros, cons, cost, maintenance.

Materials & tools

Materials

• Decking boards (composite/PVC/wood) + brand-approved clips or exterior screws

• Sleepers or joists (pressure-treated ground-contact, or composite framing)

• Pads (rubber/HDPE) or adjustable pedestals

• Flashing/joist tape for the tops of sleepers/joists

• Shims (if using sleepers)
  
  

• Fascia/trim and vent screen for open edges

• Concrete patch (if needed), construction adhesive (optional, for trim only)

• Concrete anchors (only if restraining to slab—not to the house)

Tools

• Tape measure, chalk line, laser level or long level, straightedge

• Drill/driver, impact driver, masonry bit (if anchoring into slab)

• Circular or miter saw with appropriate blade, jig saw for notches

• Safety gear: eye/ear protection, dust mask, gloves, knee pads

• Broom/pressure washer, grinder or rub brick for high spots

Read more: Which deck material stays coolest in summer?

Spacing & layout rules (pin this near your saw)

• Joist/sleeper spacing:
  
  

• 16" on center (406 mm) for straight-laid boards

• 12" on center (305 mm) for diagonal patterns or as your decking brand requires

• Board gaps: Follow your decking brand (commonly ⅛"–3⁄16" / 3–5 mm between boards).

• Perimeter gap: Leave ½" (12 mm) at walls and curbs for movement and cleaning.

• Airflow: Keep a continuous water/air path under the deck—don’t dam the slab with blocking or solid fascia.

• Fasteners: Use stainless or coated exterior fasteners; prefer hidden clips on composites/PVC for clean looks and even spacing.

Read more: Slip-resistant deck options for rainy climates?

Step-by-step installation

Step 1 — Inspect and prep the slab

• Clean thoroughly: sweep, power-wash, and let it dry.

• Check slope: water should move away from the house. Hose-test any low spots.

• Repair small spalls and fill cracks as needed. Grind down obvious high ridges so pads or pedestals sit flat.

Step 2 — Plan your layout

• Choose board direction (along the long side usually looks best).

• Snap chalk lines for the first and last rows of sleepers/joists. Mark centers at 16" O.C. (or 12").

• Mark the perimeter gap and any door transitions. Decide if your deck will follow the slab’s slope or be perfectly level (with pedestals).

Step 3 — Place pads or pedestals

• Pads (low-profile): Set them every 16–24" under sleepers. Double up under future high-traffic zones.

• Pedestals (adjustable): Space per the manufacturer (often 2–3 ft apart). Dial to your target height. Keep under-deck channels clear for water.

Step 4 — Set sleepers/joists

• Lay out sleepers or joists along your chalk lines.
  
  

• Shim as needed (sleepers), or adjust pedestal heights until the frame plane is flat—aim for ±1/8" over 10 ft (3 mm over 3 m).

• Optional restraint: You may pin sleepers to the slab with a few Tapcon anchors to limit creep (do not connect to the house). Follow your local rules.

• Treat cut ends of wood sleepers; keep all wood off the slab using pads/pedestals—no direct contact.

Step 5 — Protect the frame tops

• Apply flashing/joist tape along the tops of sleepers/joists. Press firmly so water can’t creep under the edges. This simple step greatly extends frame life.

Step 6 — Install the starter edge

• At your most visible side, install a straight starter strip (for clip systems) or a perfectly straight starter board (for face-screwed wood).

• Check square against adjacent walls—tiny twists here are obvious later.

Step 7 — Lay the field boards

• Work outward from the starter.

• Use clips or fasteners per the brand’s instructions; maintain the board gap.

• Stagger joints and add blocking under butt joints as your brand requires.

• For diagonal layouts, confirm you’re on 12" O.C. support and add extra blocking at seams and borders.

Step 8 — Borders, fascia, and vents

• Trim board ends flush or add a picture-frame border (looks premium, hides end cuts).

• Install fascia/trim with approved screws and a small gap at joints for movement.

• Add vent strip or mesh along open edges to keep critters out while preserving airflow.

Step 9 — Steps, ramps, and transitions

• If the deck meets a yard or another surface, plan a code-compliant step or a low ramp.

• For any steps on slab, use pads/pedestals under a small step frame so it breathes and drains.

Step 10 — Final checks

• Confirm fastener heads are flush, gaps are consistent, fascia is straight, and water flows freely under the deck.

• Rinse the surface to clear dust. Walk the deck—no bounce, no squeaks.

Read more: What’s the cost to build a 300 sq ft deck (DIY vs pro)?

High-quality spec table (decisions → specs → why they matter)

Cost & time snapshot (for planning only)

• Materials (pads/pedestals, sleepers/joists, tape, fasteners, decking): commonly $10–$27 per sq ft depending on the system and brand line.

• Labor/time: A simple 12'×16' (3.7×4.9 m) build is a weekend-plus for two experienced DIYers using sleepers; pedestals add setup time but save time on shimming. Complex borders, stairs, or railings push beyond a weekend.

(Always compare your decking brand’s structural and fastener requirements; they vary.)

Common mistakes to avoid

1. Screwing into the house “just to be safe.” That’s a ledger connection—don’t do it unless you’re designing a code-compliant attached deck.

2. Letting wood rest directly on the slab. It will wick moisture; always use pads or pedestals.

3. Blocking water flow with solid fascia or framing laid across the slope. Leave channels.

4. Ignoring door and wall clearances. You’ll trap debris and water; doors may jam.

5. Skipping flashing/joist tape. Small cost, big life extension.

6. Wrong spacing for the board type. Many composite/PVC boards demand 12" O.C. support for diagonals.

Read more: How Much Does It Cost to Resurface an Existing Deck? (2025 Guide)

Maintenance (10-minute seasonal checklist)

• Rinse the deck and clear leaves from edge vents.

• Check board gaps and perimeter spaces; clean them out for airflow.

• Inspect fasteners and any movement at edges.

• If you used wood, inspect and reseal cut ends if needed.

• After severe storms, confirm under-deck drainage paths are open.

FAQs

Can I do this without drilling the slab?

• Yes. A true floating deck can sit on pads or pedestals with no anchors. Some builders add a few anchors to limit creep; if you do, anchor only to the slab, not to the house.

Do I need a vapor barrier under the deck?

• Generally, no on exterior slabs. You want airflow, not sealed moisture. Keep wood elevated and the perimeter vented.

Can I use composite or PVC boards over concrete?

• Absolutely—as long as you install them on properly spaced sleepers/joists with the brand’s clips or screws, and maintain ventilation.

Should the deck be level or follow the slab?

• Either works. Following the slope keeps water moving. Levelling with pedestals gives a perfectly flat walking surface while preserving drainage beneath.

How high should the finished deck be under a door?

• Common practice is to keep 1½–2" of clearance. Always check your local rules and door manufacturer.