Open Terrace Deck

Dimensions

Cut list

Tools you'll need

• ✓

  Measuring tape (5m or longer)

  Used for measuring all materials.

• ✓

  Pencil and carpenter's square

  For marking lines and checking right angles.

• ✓

  Saw

  Using a home center cutting service is recommended.

• ✓

  Electric screwdriver

  Impact drivers improve work efficiency.

• ✓

  Sandpaper

  Prepare two types: #120 and #240.

• ✓

  Level

  Essential for checking level during assembly.

• ✓

  Clamps (2 or more)

  Used for temporary fastening during joining.

• ✓

  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 leveling and spreading crushed stone.

Materials

Build steps

1. 1

   Confirm Location and Check Ground Conditions

   ≈ 30 min

   Measure the installation site for the terrace deck (no roof) (3000×2400×300mm). Check ground levelness, sunlight exposure, ground strength (susceptibility to softening), and drainage paths.

   Measure

   W 3000 mm

   MeasureSTEP 1 / 10

   Tip

   • If the ground is soft, prepare the foundation by laying crushed stone thickly.
   • Ensure deck height allows ventilation underneath (300mm) to prevent moisture problems.
   • Check direction of rainwater flow to avoid water accumulation.

   Watch out

   • Weak ground may cause sinking and tilting over time.
   • Placing where water accumulates leads to rapid wood decay.
2. 2

   Prepare Materials for Cutting

   ≈ 30 min

   Prepare 30 pieces of Western Red Cedar deck boards (20×90×2400mm), 7 pieces of 2x4 joists (38×89×2400mm), and 5 pieces of 4x4 girder beams (89×89×3000mm). Also prepare ten 150mm square deck blocks and 420 stainless steel coarse-thread screws (90mm).

   Cut

   Use the in-store cut service

   CutSTEP 2 / 10

   Tip

   • Red Cedar is highly water-resistant and the standard for outdoor decks.
   • Selecting wood with fewer knots results in a more beautiful and longer-lasting finish, despite higher cost.
   • Stainless steel screws are essential for outdoor use. Iron screws cause rust stains that blacken the wood.

   Watch out

   • Using SPF lumber will cause decay within 3 to 5 years; deck boards must be water-resistant species (e.g., Red Cedar, Ipe).
   • Insufficient screw length fails to firmly join the joists and girder beams.
3. 3

   Install Deck Blocks and Level Them

   ≈ 60 min

   Place deck blocks (150mm square) at the four corners of the installation area. Dig into the ground to partially embed them, then use mason's line and a level to align the top surfaces of all four deck blocks horizontally. Measure to ensure spacing between blocks is consistent (approximately 450mm left-right and front-back).

   Build the frame

   Tighten joints firmly

   AssembleSTEP 3 / 10

   Tip

   • Leveling deck blocks is the most critical step determining overall levelness; spend adequate time here.
   • Mason's line allows simultaneous level checking of all four blocks.
   • Placing deck blocks slightly higher than ground improves drainage.

   Watch out

   • Uneven deck blocks cause the entire deck to tilt, causing items to roll on it.
   • Positioning deck blocks where water pools raises moisture to the wood.
4. 4

   Sand Girder Beams and Joists

   ≈ 30 min

   Sand the 4x4 girder beams and 2x4 joists starting with #120 grit sandpaper, then finish with #240 grit. This prepares the surface before painting, especially important for outdoor use. Sand cross-sections carefully to block water ingress.

   Sand

   #120

   SandSTEP 4 / 10

   Tip

   • Use knot-free and crack-free surfaces of girder beams on top since they bear the heaviest loads.
   • Joists are laid perpendicular to girder beams; maintain level surfaces on both.
   • Perform sanding outdoors to minimize dust; wear a mask.

   Watch out

   • Insufficient sanding causes poor paint absorption and early deterioration.
   • Leaving sanding dust causes uneven paint coating.
5. 5

   Apply First Coat of Paint to Girder Beams and Joists

   ≈ 60 min

   Before assembly, paint only the girder beams and joists. Pre-painting the connection surfaces, which are inaccessible after assembly, improves durability. Apply outdoor wood preservative (e.g., Xyladecor) thoroughly and allow 24 hours drying.

   Paint

   Watco oil / varnish

   PaintSTEP 5 / 10

   Tip

   • Pre-painted joining surfaces greatly enhance post-assembly wood preservative performance.
   • Apply extra preservative to cross-sections.
   • Focus preservative on components closer to the ground due to higher decay risk.

   Watch out

   • Assembling before painting leaves uncoated joint surfaces vulnerable to moisture and decay.
   • Rain during drying washes away the coating; check weather forecast before painting.
6. 6

   Attach Girder Beams

   ≈ 45 min

   Lay five girder beams (89×89×3000mm) parallel on the deck blocks with 450mm spacing. Insert a waterproof sheet between girder beams and deck blocks to prevent capillary water rise. Secure from beneath with stainless steel screws or special connectors. Use a level to verify all four points are level.

   Build the frame

   Tighten joints firmly

   AssembleSTEP 6 / 10

   Tip

   • Inserting a waterproof sheet (rubber sheet acceptable) prevents capillary water from rising into the girder beams.
   • Dedicated connectors ('deck block connectors') strengthen attachment and can be sourced from hardware stores.
   • Align girder beam direction with water drainage flow.

   Watch out

   • Omitting waterproof sheets causes water rise and rot in girder beams.
   • Uneven girder beams cause the entire deck to tilt.
7. 7

   Attach Joists

   ≈ 45 min

   Place seven joists (38×89×2400mm) perpendicular on two girder beams spaced at 300mm. Drill 5mm pilot holes through the joists and screw two 90mm stainless coarse-thread screws per connection (8 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; 4x4 lumber is thick but prone to splitting.
   • Check and maintain the joist top surface level when fastening.

   Watch out

   • Joist spacing over 500mm causes decking boards to bend under load.
   • Short screws that do not reach girder beams compromise strength.
8. 8

   Attach Deck Boards

   ≈ 60 min

   Lay 30 Western Red Cedar decking boards (20×90×2400mm) perpendicular to joists. Insert 5mm gaps between boards by spacing with a 5mm thick spacer (thickness of a nail). Drill 3mm pilot holes into the joists under each board and drive two 50mm stainless steel screws into each board (total 18 screws).

   Build the frame

   Tighten joints firmly

   AssembleSTEP 8 / 10

   Tip

   • 5mm gaps ensure water drainage and ventilation; closing gaps traps water.
   • Use 5mm thick spacers to maintain uniform gaps.
   • Install boards with concave side down (joist side) considering board warp; convex up causes discomfort when walking.

   Watch out

   • Omitting gaps causes water pooling and decay underneath boards.
   • Screws set too close to edges cause end splitting.
9. 9

   Sand and Paint Deck Boards

   ≈ 90 min

   Sand the entire deck boards starting from #120 grit then #240 grit, focusing on surfaces, edges, and end grain. Remove sanding dust then apply two coats of outdoor wood preservative: coat one, dry 24 hours, then coat two and dry another 24 hours.

   Paint

   Watco oil / varnish

   PaintSTEP 9 / 10

   Tip

   • Sanding opens wood pores, improving paint absorption.
   • Apply extra preservative on end grain.
   • Choose stainless steel fasteners; iron fasteners rust within one year.

   Watch out

   • Missed spots allow moisture intrusion and decay; paint thoroughly.
   • Rain before drying causes paint to wash off; check weather forecast before painting.
10. 10

    Final Inspection and Maintenance Plan

    ≈ 30 min

    Verify all screws are tight, boards are level, gaps are even, and paint is uniform. Test drainage by pouring water. Avoid placing heavy objects on the deck on the first day until paint fully cures. Annual repainting maintains deck durability for over 10 years.

    Done!

    Done — nice work!

    DoneSTEP 10 / 10

    Tip

    • Lightly sand with #240 grit annually before repainting to extend deck life beyond 10 years.
    • Remove leaves and mud monthly from underneath to cut moisture sources.
    • In cold regions, paint before winter to maintain protection until spring.

    Watch out

    • Skipping annual maintenance causes paint peeling and decay within 2-3 years; yearly repainting is key.
    • Neglecting debris under deck sustains humidity and leads to decay from below.

Warnings

• ⚠️Wood preservative coating is mandatory for outdoor use (recoating recommended annually).
• ⚠️Use stainless steel screws (iron screws will rust).
• ⚠️Drill pilot holes before screwing to prevent wood splitting.
• ⚠️Place deck blocks level (tilting causes joist distortion).

Find more blueprints in this category or store