Gather your supplies
- Wall plate 190 x 45 x 5210mm treated pine
- Bearer 190 x 45 x 5300mm treated pine
- End joists (2) 190 x 45 x 2955mm treated pine
- Normal joists (8) 190 x 45 x 2910mm treated pine
- Posts (4) 90 x 90 x 750mm treated pine
- Blocking (9) 140 x 45 x 539mm treated pine
- Decking (21) 140 x 22 x 5400mm merbau
- Short edging (4) 90 x 19 x 3000mm merbau
- Long edging (2) 90 x 19 x 5338mm merbau
You'll also need
12 or 16mm-dia x 8m clear plastic tube; food dye (optional); galvanised joist hangers FB45180 (16); concrete mix (1-2 bags per post); 14mm coarse aggregate (1-2 bags); 10mm masonry bit; 120mm galvanised cuphead bolts and nuts (8); 100 x 10mm galvanised Dynabolts (10); 125mm batten screws (8); stainless-steel decking screws; Cabot’s Natural Decking Oil.
Decide on deck size. Here, it is 5.3m long x 3m wide, great for using standard 3m and 5.4m timber lengths with little wastage. Mark length of deck (5.3m) on wall of house. Decide on height of deck (here, it is same height as door threshold). Measure down 22mm (thickness of decking) and mark at each end of door opening.
To transfer marks to ends of deck, set up a water level. Fill plastic tube to within 200-300mm of top with plain or coloured water. Flick to remove air bubbles. Because water finds its own level, the water at each end of tube will be same height. With a helper, hold tube at door and far end of deck. Move tube up and down under door until water steadies on mark, then mark this height on wall at far end. Repeat at other end.
Place wall plate and bearer on saw stools and cut to length. Measure 45mm from each end of bearer and align ends of plate with these marks. On bearer, measure position where joists will meet bearer, here 45mm, then 539mm, then 45mm, and so on to centre. Do the same back the other way. Adjust to allow for wall vents, if any. Square across both plate and bearer. Nail 1 side of joist hanger to each of the 8 inner joist positions on plate and bearer so bottom of hanger will support joists at same height as bearer and plate. Don’t fit joist hangers to ends of wall plate or bearer.
Measure 45mm in from end marks on wall for length of wall plate. Measure distance to any vents the wall plate may cover and cut plate to leave vents clear. Prop wall plate against wall on timber offcuts or bricks. If wall plate runs into ground at high end, remove a little off bottom so it’s clear of ground. Predrill 10mm holes through wall plate every 600mm or so, using a wood bit, then use masonry bit in brickwork. Secure wall plate with 10mm Dynabolts.
At each side of vents, secure wall plate with Dynabolts, making sure every section of plate has at least 2 Dynabolts.
For width of deck, work to decking board sizes. These boards are 140mm wide and will be laid with a 4.5mm gap, so 21 decking boards and spaces give a total deck width of 3035mm. Allowing for a 35mm decking overhang, measure 3000mm square from house at each end of deck. Use the 345 rule to ensure you are square to house wall. Stretch a stringline parallel to wall. From each end of stringline, measure 345mm and 1885mm. Mark these 4 points on ground as post hole centres.
At each mark, dig a 250mm-dia x 600mm-deep hole, centred 45mm inside line. Use blocks or bricks to securely prop bearer in place over holes. Using water level, adjust height until top of bearer and wall plate are at same height.
Recheck distance from wall with tape measure. If bearer is too deep at 1 end, as here, remove some underside of bearer (here 30mm) so top of bearer will sit level at right height.
Pour 100mm of 14mm coarse aggregate in each hole. Use a spirit level to mark post positions on bearer so they will be centred in holes. Measure difference between top of aggregate and top of bearer to give post lengths. Cut to length and mark where each post goes.
Cut a 190 x 45mm notch in top of each post, then clamp to bearer and check for plumb. Drill through for 2 cuphead bolts, insert bolts, add a washer and wind on nuts. Tighten with a ratchet.
Screw 2 end joists to ends of wall plate, and screw bearer to joists, using 125mm batten screws. This gives basic rectangle of deck. At this stage, with your helper, measure diagonals of deck, which should be 6090mm. If they are equal and length of opposite sides are equal, the deck will be square.
Insert joists into joist hangers and close hangers. Then nail hangers to joists and to wall plate and bearer.
Install blocking down centre of deck frame to help stop joists twisting. Offset each second block so it’s easy to fix them in place. The top of each block is 25mm down from tops of joists.
Check again that deck frame, still supported on props, is square, and level in all directions. Adjust props, as necessary. Mix and pour concrete into holes with posts and tamp down so there are no air pockets in concrete. Allow concrete to set overnight.
If you can, buy decking boards in full 5.4m lengths. Select straightest decking board to use for outside edge of deck. Align with edge of deck so there is at least a 35mm overhang at ends and exactly a 35mm overhang along front edge. Screw down to end joists using decking screws. With 2 ends fixed, check edge decking board is dead straight. To do this, partly drive a nail into each end of board, then stretch stringline taut around edge. Place matching pencils or similar between string and board. This taut string will be straight, as long as it doesn’t touch board. Maintain same gap between string and board and first piece of decking will be straight.
Push decking into position at centre and drive in a screw. A second pair of hands may be useful. It’s easier to drive screws if you predrill.
Continue to lay decking using 4.5mm-dia nails or similar as spacers. Tap them in so they just hold, as they need to come out easily. At this stage, only screw down decking at each end and in centre, ensuring screws will be in line with each other. If decking boards are bowed, straighten them with a broad chisel, using either adjacent board to lever decking out if curving in, or tapping blade of chisel into joist and using chisel as a lever to pull board into line if it curves away from adjacent board. It’s also worth checking every 7 decking boards that combined width is same at each end and in centre. As there is 1 less gap than boards, the total width of 7 boards should be 1007mm.
With all decking boards down, draw faint straight lines across decking for screw positions, then drive in remainder of screws, using chisel to adjust gaps between boards, as needed. Once all boards are finally fixed, trim ends of deck by measuring 35mm from joist, drawing a line across boards, then cutting with circular saw. Finish end of cut near wall with a handsaw.
Cut and fix edging to cover face of bearer and joists. Leave a 5mm gap between boards. Allow deck to weather for a few days or weeks. Then coat with 2 or more coats of decking oil to bring out colour and protect timber. Repeat every 6-12 months to maintain timber colour, but this is as easy as sweeping the deck if you use a decking oil applicator.