To lay garden decking, set firm footings, frame treated joists level, then fix deck boards with gaps and corrosion-resistant screws.
Want a neat, durable deck without headaches? This step-by-step walks through planning, marking out, framing, fixing boards, and finishing so water drains, screws stay tight, and the surface feels solid underfoot. You’ll see clear checks, build-order tips, and small tweaks that prevent costly redo work.
Tools And Materials Checklist
Gather the kit first so the build flows. Use structural, pressure-treated timber for the frame and exterior-rated fixings throughout.
| Item | Why You Need It | Notes |
|---|---|---|
| String Lines & Pegs | Mark the footprint square and level | Crossed strings locate true corners |
| Tape, Square, Spirit Level | Keep lines straight and flat | Laser level helps on slopes |
| Post Holes & Concrete | Create stable pads or footings | Fast-set mix speeds the job |
| Treated Joists/Beams | Carry the deck load | Seal cut ends before assembly |
| Deck Boards | Walking surface with drainage gaps | Softwood, hardwood, or composite |
| Stainless/Coated Screws | Secure boards and framing | Exterior grade only |
| Joist Hangers & Angles | Fix joists to beams safely | Match to timber size |
| Weed Membrane & Gravel | Suppress growth and improve drainage | Lay under the deck area |
| Spacers & Packers | Keep board gaps consistent | Plastic shims won’t crush |
| Saw, Drill/Driver, Bits | Cut, pre-drill, and fix | Sharp blades reduce tear-out |
| Safety Gear | Protect eyes, hearing, hands | Gloves grip wet timber |
Lay Decking In A Garden: Step-By-Step
1) Pick The Spot And Size
Pick a zone with the light you like and a simple route from the house that won’t drag mud across boards. Sketch the plan with clear dimensions, then decide board direction and border style. Leave room at edges for airflow and future access to gullies or pipe cleanouts.
2) Check Rules And Heights
Many areas allow low platforms without a formal application, subject to limits on height and area. In England, raised platforms up to 30 cm and covering under half the garden generally sit within permitted development; see the Planning Portal page for the exact wording and local exceptions: decking rules.
3) Prepare The Ground
Strip turf inside the outline and dig out soft spots. Lay a weed membrane and cover with compacted gravel. On clay or wet soils, add more depth so water can pass under the frame. Keep drainage channels open at the perimeter.
4) Set Footings Or Pads
Mark pad positions to suit joist spans and beam size. For a small platform, concrete pads at 1.2–1.8 m along beams work well; larger spans need more support. On a slope, step pad heights so the top surfaces align on a level plane. Bed post bases or composite risers while the concrete is green so layout stays true.
5) Build The Perimeter
Cut beams to length, crown up, and seat them on the pads. Check the rectangle with the 3-4-5 method or by matching diagonals. Fix temporary braces, then install joist hangers at a consistent spacing that suits your board type and span.
6) Fit Joists And Keep Them Level
Drop joists into hangers and lock them off. Plane high spots or use non-compressible shims where needed so the tops sit on one flat plane. Add blocking to stop twist and to give solid edges for borders and steps. Leave a small gap from masonry so air can move along the wall.
7) Flashing, Venting, And Clearance
Where the frame meets a wall, fit proper flashing to kick water out over the boards. Keep a vent gap along the house face and a healthy void under the frame so it can dry after rain. Slatted screens, open skirting, or mesh vents keep airflow while hiding the underside.
8) Pre-Finish Cut Ends
Whenever you trim treated timber, brush on an end-grain sealer before assembly. This quick step limits water uptake at cuts and keeps treatment performance consistent.
9) Lay The Boards
Start with the board that sets the sightline—often along the house or at the visible edge. Use spacers for a consistent gap. Keep fasteners in line and the same distance from each edge. Stagger butt joints over solid support, never in free span. Sight down the run and nudge boards so the field looks straight.
10) Trim, Edge, And Finish
After fixing, snap a line and trim any overhang. Fit fascia or a picture-frame border to hide end grain. Clean the surface and, for softwood, add a penetrating oil after the first dry spell to slow checking.
Sizing Details That Keep Decks Solid
Correct spacing and fixings give a firm feel and fewer squeaks. Many trade sources and board makers converge on simple ranges. Softwood boards often sit on joists at 400–450 mm centres; some composites ask for 300–400 mm. Always check the installation sheet for your product. For fixings, use deck screws that bite well into the joist. The Timber Decking and Cladding Association advises screw length around two and a half times the board thickness and placing screws about 25% in from each edge and 25 mm from ends; see the TDCA’s deck screw guidance.
Ventilation And Board Gaps
Airflow below the frame lets the structure dry between showers. Leave clear slots for cross-venting at edges and keep soil or mulch back from the fascia. Use board spacers so rainwater runs off and through the field. In shaded plots or near planting, choose the wider end of the typical gap range.
Timber And Board Choices
Softwood boards give a friendly price and easy cutting. Go for pressure-treated stock that suits outdoor use. Hardwoods resist wear and dents and hold crisp edges; pre-drill to prevent splits. Composites bring color stability and low upkeep; follow the maker’s gap and joist rules closely, since spans and clip systems vary.
For the substructure, many UK trade guides align with BS 8417 and recommend a treatment grade suitable for exterior structural duty for posts, beams, and joists that carry the load. Use joist tape on beam tops to shed water away from fastener penetrations.
Board Direction, Borders, And Drainage
Run boards along the longest sightline to reduce butt joints, or across the shortest span to raise stiffness. A picture-frame border hides cut ends and gives a clean edge at steps and planters. Keep a gentle fall away from the house so surface water clears quickly. Gap consistently across the field so drainage stays even.
Cut-List Planning And Layout Tips
Good prep saves timber and time. Draw a simple scale plan and count joists, noggins, and hangers. Decide where butt joints land so every joint sits on a joist with two screws per board end. If you want a border frame, add blocking under the picture-frame courses and miter corners on a backing strip for strength.
Common Sizes And Spacing
The table below lists practical ranges used on many builds. Always defer to local codes and your board maker’s instructions.
| Element | Typical Range | Notes |
|---|---|---|
| Joist Centres | 300–450 mm | Composites often tighter |
| Board Gap | 4–6 mm | Wider near planting |
| Screw Length | ≈ 2.5× board thickness | Exterior screws only |
| End Distance | ~25 mm from board ends | Pre-drill dense timber |
| Edge Distance | ~25% in from each edge | Gives clean lines |
| Ground Clearance | As high as design allows | Aids airflow and drying |
Detailed Build: From String Lines To Last Screw
Square The Footprint
Knock in pegs and run string lines. Set width and length, then tweak until both diagonals match. Mark footing spots on the ground and spray a quick dot so they don’t vanish while you dig.
Set The Pads
Dig holes below topsoil. Tamp the base, pour concrete, and trowel tops level to a shared datum. Drop in post bases while the mix sets so they line up. Re-check the rectangle before the mix cures.
Install Beams And Joists
Seat beams on bases and fix to anchors. Fit joist hangers at your chosen spacing and set joists with crown up. Add blocking mid-span and at borders. A straightedge across several joists shows where to shave or pack to keep a flat plane.
Flash And Protect
At the wall, run flashing behind cladding or render and over the deck edge. Cap beam tops with joist tape to shed water from screw penetrations. Keep soil or bark away from beam sides so air can reach the timber.
Board Laying Pattern
Decide on the look: all boards parallel, or a picture-frame border. Pre-drill dense hardwoods. Keep screw heads just below the surface, not buried. Strike a chalk line every few rows so each course stays straight across the span.
Stairs And Edges
For steps, fix stringers to a solid bearer and use the same board gap on treads. Add a nosing strip or a border board for grip and a crisp finish. Fit edge trim where the deck meets gravel to stop small stones dropping between boards.
Safety And Durability
Wear eye and ear protection when cutting and driving. Handle treated timber with gloves and wash up after work. Keep a tidy site so offcuts and screws don’t cause trips. Where a platform is high, add balustrades and check loading where groups gather.
Weather Windows And Curing
Pick a dry spell for pouring pads and fixing boards. Wet timber can shrink as it dries, so keep gaps consistent across the field rather than butting boards tight. Let oil finishes soak in during a dry, mild day.
Fastener Choices And Patterns
Use stainless or polymer-coated deck screws on all boards. Two per bearing, in line with the grain. Hidden clip systems can work on many composites; follow the maker’s spacing rules closely. For framing, use structural screws or bolts sized for the hangers and connectors you select.
Troubleshooting Quick Fixes
Boards Cupping
Look for trapped moisture under the frame. Open up ventilation paths, trim landscaping back, and check that gutters aren’t dumping water near the platform.
Squeaks Or Bounce
Add blocking, tighten screws at joints, and confirm joist centres suit the board type. If spans are wide for the product, insert extra joists between existing ones.
Dark Marks Around Screws
That points to corrosion. Replace with stainless fixings and, where staining is heavy, sand and oil the surface once dry.
What To Budget
Cost swings with size, timber grade, fixing type, and site prep. A modest softwood platform built on pads costs far less than a raised hardwood structure with long stairs and a border frame. Price the frame first, then add boards, fixings, finishes, and disposal of spoil. Include waste allowance so a last-minute run to the merchant doesn’t stall the day.
Why This Method Works
You’re building a flat, well-drained platform on a stable base with the right treatment, fixings, and airflow. Those elements keep movement low, water moving, and screws tight. Follow the order above and the result stays straight, quiet, and good-looking through the seasons.