To raise deck height, cut new joists to suit distance from top of existing joists to top of door sill, less 25mm for thickness of decking, here 85mm. Nail new joists across existing, spaced at 450mm from centre to centre. Use top of joists to set levels for boardwalk.
To set out boardwalk, run stringlines where edges of boardwalk will be. Ensure they are square to house and parallel. Also set out to extend deck partially along its width. Make end of this extension a multiple of 145mm plus 50mm from house to suit decking board width.
Mark ground for long (handrails) and short (lawn side) posts. Space posts evenly between house and edge of circular area not exceeding 1800mm apart. Along side where handrail will be, outer face of post should meet stringline. Along sides that meet lawn and circular area, outer face of posts should be 50mm from stringline. Use post-hole digger to dig holes for handrail posts 700mm deep. Along lawn sides, dig holes 300mm deep.
Place posts in holes, make plumb and concrete in position. Posts for handrail should be at least a metre above decking level while top of short posts on lawn sides should be
at least 25mm below decking level.
Along lawn sides and where it goes into circular seating area, install sleepers against outside of short posts to retain soil. Top of sleepers should be at decking level. Screw through sleepers into posts.
Nail bearers against both sides of handrail and short posts, flush with outer face of posts. Top of bearers should be 165mm below decking level. At end of deck extension, run a bearer along the short posts. Screw bearers to posts using 2 screws per bearer per post.
Place joists on bearers. Make joists between handrail posts flush with outer face of posts. Joists on lawn side should sit against short posts. Space intermediate joists between these at 450mm centres. On deck extension, align joists with those on the deck so decking nails will be in line.
Starting from house, lay decking. Leave a 5mm gap to house and use plastic packers to space following boards 5mm apart. Every 5 or so boards, measure to end of deck and deck extension at a number of points to ensure boards are running square. If measurements are different, adjust gap slightly on subsequent boards until they are the same. Butt ends of boards into sleepers and make flush with joist along side with handrail.
Cut decking to fit around handrail posts. To support cut ends, nail blocking to side of posts.
Along handrail side, fix decking boards to side of deck so edge is flush with top of boards.
Mark handrail posts 955mm above deck. Use power saw to cut posts at this mark.
Place handrail on top of posts. Predrill and screw through handrail into posts. Join handrail over posts, as required.
Prepare and paint exterior walls, handrail, any pergola, doors, windows and architraves as outlined in materials list.
Apply decking oil to deck to protect and maintain it.
Use 50mm galvanised wood screws to attach a pre-painted length of decking to inner side of handrail posts, 5mm above decking. This acts as a wheelchair stopper.