GuidePatios & Paths
How to Build a Ground-Level Floating Deck
A floating deck sits just above the ground on concrete blocks instead of posts dug deep into the soil. It is not attached to the house, so it is a manageable first decking project and a quick way to turn an uneven corner of the garden into a level seating area.
What you will build
You will level and prepare the ground, set concrete deck blocks in a grid, build a rectangular frame of joists on them and screw decking boards across the top. The deck stays low, typically a few inches to about a foot above the ground.
Joist size and spacing depend on the lumber you use and the decking board's maximum span; many decking boards are made for joists at about 16 in (40 cm) centres, but always check the decking manufacturer's instructions. Even low decks may be covered by local rules in some places, so check before you start.
Real-world examples
Photos of similar builds by other people, shared under open licenses. They show the idea in practice; the details differ from this guide.
Materials
- Concrete deck blocks (precast piers), enough for a grid under the frame
- Framing lumber for rim joists and joists, rated for ground contact if close to the soil
- Decking boards (wood or composite) and the screws or hidden fixings their maker specifies
- Joist hangers and the specified nails or structural screws
- Weed-control fabric and gravel for under the deck
- Exterior wood screws
- End-grain preservative for cut ends of treated lumber
Tools
- Tape measure, string line and stakes
- Long spirit level or laser level
- Spade and a tamper
- Circular saw or mitre saw
- Drill/driver and impact driver
- Speed square
- Safety glasses, hearing protection, knee pads and gloves
Step by step
1Mark out and prepare the ground
Mark the deck's outline with stakes and string, and check the diagonals so it is square. Remove turf and a few inches of topsoil, level the area roughly and compact it. Lay weed-control fabric and cover it with gravel so water drains away and weeds cannot grow up through the boards.
2Place the deck blocks
Set blocks at the corners, along the edges and in a grid under the joists, at the spacing your joist size allows. Bed each block on compacted gravel and check them with a long level or laser so their tops are all at the same height. This is the most important step: a level grid means a level deck.
3Build the outer frame
Cut the rim joists and screw them together into a rectangle on top of the blocks. Measure the diagonals again and adjust until they are equal, then check the frame is level in all directions.
4Fit the inner joists
Fix the inner joists between the rim joists with joist hangers, at the spacing your decking requires. Make sure each joist sits on blocks along its length and that the crowns (slight upward bows) all face up.
5Lay the first board straight
Start with a full board along the most visible edge and screw it down, checking that it is perfectly straight. Every other board follows this one, so take your time here.
6Lay the rest of the decking
Work across the frame, leaving the gap between boards that the decking maker recommends so water drains and the boards can swell. Use spacers for even gaps, drive two screws per joist, and stagger the board joints so they do not line up.
7Trim the edges and finish
Snap a chalk line and cut the board ends in one straight line, then fit a fascia board around the frame if you like. Treat cut ends of treated lumber, and apply an oil or stain if your decking needs it.
Tips for a better result
- Pre-drill near board ends to stop splitting, especially with hardwoods.
- A slight fall of the ground away from the house helps drainage under the deck.
- Leave a gap between the deck and any house wall so the deck does not trap water against it.
- Buy all decking boards from the same batch so the colour matches.
Common mistakes to avoid
- Setting the blocks by eye instead of with a level, so the deck rocks.
- Joist spacing wider than the decking boards allow, giving bouncy boards.
- Butting boards tightly together with no drainage gaps.
- Laying the deck straight on soil without a gravel layer, so the frame stays wet and rots.
Safety
- Lift with your legs and get help with long boards and concrete blocks.
- Wear eye and hearing protection when cutting, and a dust mask when cutting treated wood or composite boards.
- Use knee pads; you will spend hours kneeling.
- A deck higher than a low step may need railings and may fall under building rules; this guide covers ground-level decks only.
General guidance only. Follow the instructions for your tools and materials and your local rules, and use a qualified professional for electrical, gas and structural work.
Finishing up
A floating deck gives you a level, dry outdoor floor in a weekend or two, without digging deep footings. Sweep leaves out of the gaps each autumn and re-oil wood decking when water stops beading on it, and it will look good for years.
About this guide: written by the DIY Outdoor Builds editors from general, widely used building and gardening practice. Text and illustration © DIY Outdoor Builds. Photos are by the people credited under each one, used under their licenses. Found an error? Let us know.
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