DIY - $4250 (Have it done for $7120)
Skill – 7/10
Time - 8 days
A pergola provides the ultimate in backyard relaxation during summer, especially in a sunny backyard. They provide shade from the hot summer sun when covered with bamboo or a shade cloth, and in winter the covering can be removed to allow sun to stream through.
This sunny poolside had a bare patch of ground adjacent to the paving, so a pergola was built above a freestanding deck to create a stunning resort-style relaxation area.
Seven 90 x 90mm posts support the pergola, with the existing shed corner post serving as the eighth, front right post. Four back posts support the rear beam.
Rafters span the beams, with battens fixed perpendicular to the rafters to support the bamboo roofing.
Preparing the site
Measure and peg out the deck area, removing vegetation and debris. The pergola post setout was measured from the corner of the existing shed, along the angled pool paving header course, with a post positioned on the change of angle so the shape of the deck matched the paving.
Set stringlines for the back and centre-lines of the stump posts, marking post positions with pegs.
Excavate the holes to 400mm-square and 600mm-deep using a posthole digger if the ground is soft, or hire a powered auger.
Concrete can be mixed on site using a ratio of four parts aggregate (gravel), two parts fine-grain sand and one part cement. Set the posts in concrete with 100mm of gravel for drainage. Concrete the deck stumps when the pergola is finished.
Building the deck
The raised merbau deck is positioned adjacent to the existing paving. Bearers are secured to the posts clear of the ground, creating a step up.
The deck is set on 140 x 45mm treated-pine bearers and 90 x 45mm joists, with bearers supported by 90 x 90mm pergola posts and a central row of 100 x 100mm stumps equally spaced between pergola posts to support the intermediate bearers.
Tips for building a low deck
- Surface: Grade the ground to provide surface drainage.
- Ventilation and access: Make sure there is ventilation under and around the deck, and access for inspection and maintenance.
- Timber: Select a timber species that meets building regulations. Check your choice when you submit the plans to council.
- Fixings: Use hot-dipped galvanised or stainless-steel nails, screws, bolts and framing anchors.
- Bracing: Prevent lateral movement of deck and pergola by embedding posts in the ground and securing lattice panels between back posts. Provide additional bracing by adding double diagonal braces at 90º at the top corners of posts.
To align the front of the pergola posts with the edge of the header course, lift four pavers at each front post to excavate the holes and position the posts 10mm outside the paving line. When the concrete is set, re-lay the pavers.
Position the corner posts and plumb and cross-brace. Clamp 40 x 19mm braces to the posts and secure to ground pegs. Concrete around the posts, tamping and sloping the tops for drainage. Position the intermediate posts and concrete.
Transfer the height to the posts using a straight edge and spirit level, marking a square line around the posts to cut away excess with a circular saw.
TIP Use a water level for accurate measurements.
House the top of the back corner posts and the left front corner post at 190 x 45mm for the beams. Cut a 45 x 45mm notch from the outside edge so the outside rafters slot over beams.
TIP Seal all cut treated-pine surfaces.
Set a circular saw blade 45mm deep and make a series of cuts about 7mm apart to the height of the housing, removing the waste with a sharp chisel and hand plane.
TIP Test-fit a beam offcut to ensure it’s flush.
Allowing a 500mm overhang at each end, cut the beams with a circular saw to match the rafter end template. Lift the beams into place, mark the rafter position on the face of the beam and clamp the beam to the post.
Use a short and long beam along the front and back line of the posts, clamping on the centre-line of the housing. Drill two 10mm clearance holes, securing with M10 x 100mm galvanised cup-head bolts through the centre of the overlap.
Position the end rafters across the beams to mark the notches. Lay the template on the ends and set out the rafter ends from the notches. Position the end rafters over the front and back beams, tapping hard up against lugs on corner posts.
Clamp the rafter to pull it hard against the beam, skewing a nail through the rafter and into the beam to hold it in place. To secure, attach galvanised framing anchors on either side of the rafter and fix to the beam with galvanised clouts.
Space the remaining rafters, marking the positions on the front and back beams at maximum 900mm centres. Measure the length of the rafters before cutting and preparing. Secure rafters as for Step 9.
Space battens at 600mm centres with 500mm overhang and butt-join at the centre-line of the rafters. Position the first and last batten above the front and back beams, securing all battens with 65mm x 8g stainless-steel decking screws.
Cut four bearers to length. Set levels at the pergola posts, cut 10mm checkouts for the bearers and secure with two offset M10 x 130mm bolts. Position the first and last joists on the bearers, securing with 75mm x 14g batten screws.
Space the stumps at maximum 1300mm centres and cut a 140 x 45mm housing on each. Position the intermediate bearers on stumps, using M10 x 100mm bolts to secure (see Diagrams 4 and 5). Concrete the stumps, sloping the top for drainage.
Cut joists and mark the spacing at 450mm centres perpendicular to bearers, following set stringlines. Skew-nail either side of the joists into bearers with 75mm x 3.15mm galvanised bullet-head nails. Trim the overhang even with the posts.
Since the decking isn’t square on the ends, provide a fixing point for the boards and fascia by cutting two 90 x 45mm end trimmers to fit between the joists. Drill 2mm pilot holes and secure with 50mm x 8g decking screws.
Secure a starter board then lay six boards at a time. Mark the centre-line of the joists on the boards, drill two 2mm pilot holes and countersink with a combination bit. Space boards using 50 x 2.0mm nails, securing with 50mm x 8g decking screws.
Stretch a stringline aligned with the outer face of the posts at each end then use a hand or circular saw to trim the decking boards level with the posts and sand all cut edges.
TIP If using a circular saw, position a straight edge for accurate cutting.
Cut the fascia to length with angled cuts at the change of angle along the front and at the corner. Position the fascia and secure to the joists and end trimmers using two 65mm x 8g stainless-steel