For a professional look when using timber slats between two points, keep gaps between slats the same.
• Decide on your preferred gap (say 30mm) and add this to the width of your slats (90mm). Divide this number into distance between points (say 2720mm). Round out to the nearest whole number for number of slats (here, 23).
• Multiply slat width by 23 (2070) and subtract combined slat width from distance between points.
• Divide remainder (650) by number of gaps (here, same as slats as there is a gap at top and none at bottom), giving 28.3mm as exact gap width.
Gather your supplies
• Post nailing plates 90 x 22mm treated pine decking
• Timber posts 88 x 88mm primed treated pine
• Ceiling joists 90 x 35mm treated pine
• Screen 90 x 22mm treated pine decking boards
• Ceiling battens 90 x 45mm treated pine
You’ll also need
50mm countersunk metal screws; cordless drill; power saw; 75 x 75mm galvanised bracket; 6mm masonry drill bit; ShureDrive masonry anchors; 65mm 14g hex head timber screws; 120-grit sandpaper; Cabot’s Exterior Varnish Stain in Native Mahogany; Berger Jet Dry Non Slip in Clear Concrete; Dulux Weathershield Low Sheen in Domino; 40mm galvanised bullet head nails; 25mm hex head metal screws; 40 and 100mm treated pine screws; Pryda Multigrip brackets
Step 1 Measure existing metal posts and cut post nailing plates to length. Attach to posts using 50mm metal screws every 400mm. Offset screws from centre of post, so you don’t hit them with nails later.
Step 2 Mark 3 timber posts to cut a notch that will fit around roof beam. Measure from face of beam to face of post nailing plate. Deduct this distance from width of timber post to find depth of notch. Set power saw to this depth. Mark height of roof beam at 1 end of timber posts. Starting from this line, cut across each timber post, moving a few millimetres towards end with each cut. Knock out waste with a hammer and clean with a chisel.
Step 3 Find position for timber posts by pushing a length of pine decking against post nailing plates, then marking positions equally spaced between existing metal posts. Ensure gap between posts is no more than 900mm.
Step 4 Paint existing metal posts and roof beams. To help paint stick, give coating on metal a light sand.
Step 5 Locate galvanised brackets on slab so face of timber posts will meet line drawn between posts. Drill through bracket holes using masonry bit, then attach bracket to slab using masonry anchors.
Step 6 Cut timber posts to length so notch sits on underside of roof beam. Screw through brackets into posts using 65mm hex head screws. Use a spirit level to get posts plumb, predrill, then fix posts to beams with 100mm screws.
Step 7 To support ceiling battens, using 50mm metal screws, fix ceiling joists to sides of existing crossbeams, 45mm up from underside. To fix extra ceiling joists between roof beams, screw through joists into timber posts, also up 45mm from underside. At other end of joists, screw Multigrip brackets to side of roof beams using 25mm hex head metal screws. Screw through brackets into joists using 40mm treated pine screws.
Step 8 Paint timber posts and joists. Paint slab using a non-slip paving paint. Cut screen and ceiling battens to length, then stain. Let dry.
Step 9 Position first screen board, make sure it’s level, then nail in place. Cut spacing blocks and put on first board. Put next board on top, ensuring it’s flush at ends, then nail in place. Continue laying boards, checking level every 4 or so boards.
Step 10 Leaving a gap to roof beam, hold up first ceiling batten on the flat. Screw into ceiling joists using 100mm screws. To easily get gap to next batten while working overhead, fix a spacing block to an offcut so it will sit across top of battens. Push next batten hard against spacing block and fix in place. Occasionally check spacing by measuring to roof beam at each end and gradually adjusting spacing until measurements are same.