Large Wood Deck

Dimensions

Cut list

Tools you'll need

• ✓

  Measuring tape (5m or longer)

  Used for measuring each component.

• ✓

  Pencil and carpenter's square

  For marking lines and confirming right angles.

• ✓

  Saw

  Use home center cut service recommended.

• ✓

  Electric screwdriver

  Impact driver improves work efficiency.

• ✓

  Sandpaper

  Prepare #120 and #240 grit types.

• ✓

  Level

  Essential for checking horizontal alignment during assembly.

• ✓

  Clamps (2 or more)

  Used for temporary fixing at joints.

• ✓

  Brush and paint tray

  Used for applying wood preservative.

• ✓

  Mason's line and stakes

  Used for setting reference lines.

• ✓

  Shovel and crushed stone

  Used for ground preparation and crushed stone spreading.

Materials

Build steps

1. 1

   Site Confirmation and Ground Check

   ≈ 30 min

   Measure the installation site for the large wood deck (3600×2400×300mm). Check ground levelness, sunlight exposure, ground strength (whether it is easily muddy), and drainage paths.

   Measure

   W 3600 mm

   MeasureSTEP 1 / 10

   Tip

   • If the ground is soft, ground preparation is necessary. Spread gravel thickly.
   • Maintain a deck height of 300mm to ensure ventilation underneath as moisture countermeasure.
   • Confirm rainfall flow direction and position the deck to prevent water accumulation.

   Watch out

   • If the ground is weak, the deck may settle and tilt over time.
   • Placing the deck where water pools causes the wood to deteriorate quickly.
2. 2

   Preparation for Cutting Components

   ≈ 30 min

   Prepare 36 pieces of Western Red Cedar decking boards (20×90×2400mm), 7 pieces of 2×4 lumber joists (38×89×2400mm), 5 pieces of 4×4 lumber beams (89×89×3600mm), 10 foundation blocks (150mm square), and 504 stainless steel coarse-thread screws 90mm.

   Cut

   Use the in-store cut service

   CutSTEP 2 / 10

   Tip

   • Western Red Cedar has high water resistance and is standard for outdoor decks.
   • Selecting lumber with fewer knots yields a beautiful finish. Though costlier, it increases longevity.
   • Stainless steel screws are essential outdoors. Iron screws rust and stain the wood black.

   Watch out

   • Using SPF lumber results in decay within 3-5 years. Use water-resistant species like Red Cedar or Ipe for decking.
   • Insufficient screw length will prevent strong joist-to-beam fastening.
3. 3

   Foundation Blocks Installation and Leveling

   ≈ 60 min

   Place foundation blocks (150mm square) at the four corners of the installation area. Dig the ground to embed the blocks. Use mason’s line and a level to align the top surfaces of the four blocks horizontally. Measure distances between blocks (about 450mm spacing side-to-side and front-back) accurately.

   Build the frame

   Tighten joints firmly

   AssembleSTEP 3 / 10

   Tip

   • Leveling the foundation blocks is the most crucial step for overall deck leveling. Spend ample time on this.
   • Using mason's line allows simultaneous confirmation of all four blocks' levels.
   • Set foundation blocks slightly above ground for better drainage.

   Watch out

   • Uneven foundation blocks cause the entire deck to tilt and items may roll on top.
   • Placing blocks where water pools allows moisture to rise into the wood.
4. 4

   Sanding Beams and Joists

   ≈ 30 min

   Sand the 4×4 lumber beams and 2×4 lumber joists with #120 grit followed by #240 grit sandpaper. Since these are outdoor components, surface preparation before painting is important. Pay special attention to sanding end grain, which is a penetration path for water.

   Sand

   #120

   SandSTEP 4 / 10

   Tip

   • Beams bear the most load. Place sides without knots or cracks facing upwards.
   • Joists are mounted perpendicular to beams. Both must have level horizontal surfaces.
   • Do sanding outdoors and wear a mask to avoid inhalation of dust.

   Watch out

   • Insufficient sanding inhibits paint penetration, leading to early deterioration.
   • Leaving sanding dust on surfaces causes paint unevenness.
5. 5

   First Coating of Beams and Joists

   ≈ 60 min

   Before assembly, apply wood preservative to beams and joists only. Pre-coating joint faces which cannot be painted after assembly is key. Apply outdoor wood preservative (such as Xyladecor) thoroughly and let dry for 24 hours.

   Paint

   Watco oil / varnish

   PaintSTEP 5 / 10

   Tip

   • Pre-coating joints greatly enhances post-assembly wood preservative performance.
   • End grain should be generously coated.
   • Components near the ground are at higher corrosion risk; thorough preservative application in this sequence is essential.

   Watch out

   • Assembling before coating leaves joint faces uncoated, allowing moisture ingress and decay.
   • If rain occurs before drying, paint film may run off. Check weather forecast before painting.
6. 6

   Installing Beams

   ≈ 45 min

   Place five 4×4 lumber beams (89×89×3600mm) parallel on the foundation blocks spaced about 450mm apart. Insert a waterproof sheet between each beam and the block. Fix from below using stainless screws or specialized hardware. Confirm level at all four points using a level.

   Build the frame

   Tighten joints firmly

   AssembleSTEP 6 / 10

   Tip

   • Insert waterproof sheet (rubber sheet is acceptable) between foundation blocks and beams to prevent capillary water ascent.
   • Special foundation block hardware increases joint strength and is available at home centers.
   • Align beam length direction with natural water flow direction.

   Watch out

   • Omitting waterproof sheet allows moisture to rise and rot beams.
   • Beams not leveled cause entire deck to tilt.
7. 7

   Installing Joists

   ≈ 45 min

   Place seven 2×4 joists (38×89×2400mm) perpendicularly over two beams spaced 300mm apart. Drill φ5mm pilot holes on beams and fasten joists with two 90mm stainless coarse-thread screws per joint (eight screws total).

   Build the frame

   Tighten joints firmly

   AssembleSTEP 7 / 10

   Tip

   • 300mm joist spacing is standard support span for 20mm thick decking boards; wider spacing causes sagging.
   • Pilot holes prevent wood splitting. 4×4 lumber is thick but prone to cracking.
   • Check joist top surface level while fastening.

   Watch out

   • Joist spacing exceeding 500mm causes decking to sag under weight.
   • Insufficient screw length fails to reach beams, reducing strength.
8. 8

   Installing Decking Boards

   ≈ 60 min

   Arrange 36 Red Cedar decking boards (20×90×2400mm) perpendicular to the joists. To maintain 5mm gaps between boards, use 5mm thick spacers (equivalent to one nail thickness) while fastening. Drill φ3mm pilot holes at joints and fix each board with two 50mm stainless screws (18 screws total).

   Build the frame

   Tighten joints firmly

   AssembleSTEP 8 / 10

   Tip

   • 5mm gaps are essential for drainage and ventilation; closing gaps traps water.
   • Use 5mm spacers to ensure uniform gaps.
   • Fix boards with cupped sides downward (concave down) toward joists. Upward cupping causes discomfort when walking.

   Watch out

   • Omitting gaps causes water accumulation and backside board rot.
   • Screw placement too close to edges causes board splitting.
9. 9

   Sanding and Painting Decking Boards

   ≈ 90 min

   Sand all decking boards with #120 then #240 grit sandpaper. Sand board surface, edges, and end grain carefully. Remove sanding dust and apply two coats of outdoor wood preservative. Dry 24 hours after first coat, then apply second coat and dry another 24 hours.

   Paint

   Watco oil / varnish

   PaintSTEP 9 / 10

   Tip

   • Sanding opens wood pores, improving paint absorption.
   • Apply extra preservative to end grain.
   • Choose stainless steel screws; iron screws rust within a year.

   Watch out

   • Missed spots allow water ingress and decay; paint carefully.
   • If rain occurs before drying, paint film may run off. Check weather forecast before painting.
10. 10

    Final Inspection and Maintenance Plan

    ≈ 30 min

    Inspect entire deck. Check screw tightness, board levelness, uniform gaps, and even paint coverage. Pour water to verify drainage. Avoid placing heavy objects on the first day to allow paint to fully cure. Annual reapplication of wood preservative ensures deck lifespan exceeds 10 years.

    Done!

    Done — nice work!

    DoneSTEP 10 / 10

    Tip

    • Annual light sanding with #240 grit followed by reapplication of the same preservative extends lifespan beyond 10 years.
    • Monthly removal of leaves and mud under deck cuts moisture sources.
    • In cold regions, coat before winter to maintain protection through spring.

    Watch out

    • Neglecting maintenance outdoors causes paint peeling and decay within 2-3 years; annual repainting is key to lifespan.
    • Ignoring moisture sources like leaves and soil accumulation under the deck causes decay from below.

Warnings

• ⚠️When used outdoors, wood preservative coating is essential (reapply annually recommended).
• ⚠️Use stainless steel screws (iron screws will rust).
• ⚠️Drill pilot holes before screwing to prevent wood splitting.
• ⚠️Set foundation blocks level (uneven blocks will distort the joists).

Find more blueprints in this category or store