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How to build a decking boardwalk

Adam_W
Valued Contributor

Difficulty: Intermediate

 

Create all-weather access to your home or garden with a decking boardwalk.

 

This project uses basic decking techniques to create a functional and attractive boardwalk. You can adjust the size to suit your needs.

 

Video Tutorial

Steps

Step 1

Measure the area for your boardwalk. Use set-out paint to mark approximate location of all sides and planned location of stirrups or anchors. We positioned our anchors at approximately 1400mm centres. Centre is the middle of the timber or support you’ll be fixing off rather than measuring to an outside edge. For larger projects use string line and pegs.

 

Step 1 - measure and set out.png

Step 2

Your boardwalk won’t be carrying much weight, so you don’t need extensive footings. The corners need the most support. Dig holes for corner supports approximately 300mm on each side and 400mm deep (loose soils will require bigger holes). Dig slightly smaller holes for the additional side supports (not less than 200mm on the sides and 300mm deep).

 

Step 2 - excavate corner support holes.png

Step 3

Cut the side beams to length. Mark location on beam for the stirrups or anchors at each end and drill with 12mm bit. Position beam and bring to required height, checking level, securing on blocks and holding with clamps. In our case one end was attaching to an existing structure so we initially secured with one 125mm construction screw, later adding two more, to allow for adjustments.

 

Use shorter M12 bolts to securely attach end stirrup or anchor to side beam (this should be on the inside of the frame). Double-check levels and relevant positioning measurements before concreting corner support in place. Repeat for additional side stirrups or anchors.

 

Step 3.1 - cut side beam position and support.png  Step 3.2 - Attach supports.png

Step 4

Repeat Step three for the second side beam but before concreting in place make sure that spacing between beam is even from end to end and that the second beam is level in relation to the first.

 

Step 4 - position second side beam.png

Step 5

Measure for the end panels, cut lengths of 140mm x 45mm to suit and then secure in place with long construction screws. Your external bearer frame is now complete.

 

Step 5 - attach end panels.png

Step 6

Measure for the internal joists. These should be spaced at no greater than 450mm centres. In our case we had two internals. Cut 140mm x 45mm pieces to suit. Mark locations for joist hangers at each end and nail hangers in position with clout nails or screws. Drop joists in place and secure with a generous number of clouts or screws.

 

Step 6 .png

Step 7

Determine location for the instant foundation supports for your joists. These do not need to be at 1400mm centres as the external frame bearer supports were. In our case we ran a line of supports through the centre. If necessary level where the instant foundation will be positioned, measure for the post and cut a section of 90mm x 90mm post to suit. Use 12mm bit to drill through both the joist and post. Slip longer M12 bolts through and secure.

 

Step 7 - add instant foundations .png

Step 8

In a deck such as this blocking or bridging is added to prevent the bearers and joists rolling or twisting. These blocks go at right angles between the bearers and joists to create a grid-like pattern. We positioned ours at approximately 1000mm centres. Fix in place with 70mm bullet-head nails or use a nail gun with 70mm nails.

 

Step 8 - Fix off blocking.png

Step 9

If you are adding trim to your external bearers it is easier to do it now. If you are decking with 140mm Merbau you will find one board will totally conceal the bearers. We used 90mm treated Pine in keeping with the nearby screening.

 

If you need to paint adjoining areas or trim it’s easiest to do it now before you lay the decking boards.

 

Step 9.1 - add trim.png  Step 9.2 - paint before decking.png

Step 10

Adding edging around your boardwalk allows for the creation of a step-down point that will be dry in any weather. Excavate as needed, cut 150mm x 25mm Pine and position. Secure board with edging or plinth pegs. Hammer these in with the rubber mallet to avoid damaging the galvanising. Pre-drill timber to avoid splitting and join boards with 40mm decking screws.

 

In our case the main step area had drainage issues so we dug in an agricultural drain and covered with drainage gravel.

 

Step 10.1 - Join edging with decking screws.png  Step 10.2 - add drainage if needed.png

Step 11

Lay drainage fabric over area inside edging (this prevents the gravel from sinking into the soil) and then cover with a thin layer of drainage gravel. Then add a good layer of decorative pebble to bring to level with the timber edge. This is more cost effective than filling to the entire depth with the more expensive pebbles.

 

Step 11 - add finishing gravel and pebbles.png

Step 12

At a few points measure width for decking boards, ensuring you allow for an overhang of about 30mm on each side. Note that hardwoods can have a longer overhang, up to about 50mm. You can now cut all of your decking boards to size.

 

To speed up board installation lay cut boards out in piles of four or five boards along the length of your work area.

 

Step 12.1 - measure to check decking board size.png  Step 12.2 - lay piles of cut boards out along work area.png

Step 13

Position your first board, checking that it is straight and square. Counter-sink and pre-drill and screw down with 40mm screws. Each board must have a screw towards each edge into each joist or bearer. As you add each board use a square or straight edge to check that it is correctly aligned with the last. Tip: set your adjustable square to check distance from edge of board to bearers as you go.

 

Use a spacer to keep your gaps consistent. We use the 4mm plastic joining strips from yellow-tongue floorboards. These are sold individually as “cable feeders” as electricians often use them for mousing cables through wall cavities.

 

Step 13.1 - Counter-sink and pre-dill and start installing.png  Step 13.2 - Use a spacer for accuracy.png

Step 14

Once all boards are down you need to take the sharp edges off the boards. This looks better and stops edges chipping and splintering with foot traffic.

 

Leave your boards to settle for a few weeks before oiling (longer if hardwood).

 

Tip – if you have gaps along the front of your edging boards fill them with coarse sand. Grass will easily grow into this and it will also add excellent drainage.

 

Step 14 - sand the edges to remove sharp corners.png  Tip - fill gaps with coarse sand .png

Materials

  • Timber for bearer and joists – 140mm x 90mm H3 treated Pine
  • Decking of your choosing (we used 90mm x 22mm treated Pine)
  • Anchors or stirrups (we used 400mm x 6mm M12 fishtail anchors)
  • Cup head bolts, M12, galvanised. Lengths suitable for both stirrups and anchors (60mm) and 90mm posts (150mm)
  • 90mm x 90mm H4 treated Pine post
  • TuffBlock Instant Foundation System Deck Support
  • Quick-set concrete. Allow two 20kg bags per stirrup or post support. We used higher-strength 32MPa concrete
  • Decking screws (we used 10-8 x 50mm Climacoat treated Pine and hardwood decking screws)
  • Timber or landscape construction screws, 125mm or 150mm
  • Joist hangers to suit 45mm x 140mm joists
  • Galvanised clout nails or screws, 30mm long to secure hangers
  • 70mm galvanised bullet-head nails (or collated nails for gun)
  • Optional – Treated Pine for edging – H4 150mm x 25mm
  • Optional - Edging (plinth) pegs, galvanised, 400mm x 25mm
  • Optional – Decorative river pebbles, 20kg bags
  • Optional – Drainage gravel, 20kg bags
  • Optional – Geotextile/drainage fabric
  • Optional – Slotted agricultural drainage pipe (we used 65mm socked pipe).

Tools

  • Drill driver (two will be useful)
  • Power saw
  • Sander
  • Measuring and marking tools – tape measure, framing square, adjustable combination square, rafter square, levels of various lengths, set-out paint
  • Hammer and rubber mallet
  • String line and survey pegs (for larger areas)
  • Nail gun (optional)
  • Digging spade
  • Wheelbarrow
  • Countersink and pre-drill combination bit (to suit screw size)
  • 12mm timber drill bit
  • Quick-release clamps.

Images

Step 1 - measure and set out.png

Step 2 - excavate corner support holes.png

Step 3.1 - cut side beam position and support.png

Step 3.2 - Attach supports.png

Step 4 - position second side beam.png

Step 5 - attach end panels.png

Step 6 .png

Step 7 - add instant foundations .png

Step 8 - Fix off blocking.png

Step 9.1 - add trim.png

Step 9.2 - paint before decking.png

Step 10.1 - Join edging with decking screws.png

Step 10.2 - add drainage if needed.png

Step 11 - add finishing gravel and pebbles.png

Step 12.1 - measure to check decking board size.png

Step 12.2 - lay piles of cut boards out along work area.png

Step 13.1 - Counter-sink and pre-dill and start installing.png

Step 13.2 - Use a spacer for accuracy.png

Step 14 - sand the edges to remove sharp corners.png

Tip - fill gaps with coarse sand .png

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