Decks not only increase lifestyle options; they add functionality and spatial flow to even the smallest of homes. Built right, a deck will not only look great, it should last years and ultimately add value to your home.
When planning your new deck, there are a few things that should be factored in. These include the position of your house in relation to the movement of the sun, the proximity of your boundaries, and the direction of the prevailing wind. Think too about how you will access the deck either from your home or other parts of the property.
While a deck needs to be level, it’s visual shape need not be square in appearance. A smart design can allow for in-built planters and seating too. Recent code changes mean decks can be built up to 1.5 metres off the ground without a permit, but you must follow the building code.
Decks with a drop of one metre or more do require handrails. Check with your local council and/or building professional to make sure you comply with current regulations.
Before digging any holes, a check should also be made of your property’s plans for any underground piping, either plumbing or electrical.
Rarely will two decks ever be the same, as each site has its own characteristics. If you are going to build a deck with an elevated aspect or critical structural elements, then consult with a qualified builder, engineer and/or architect.
They will have a thorough understanding of the code requirements for each scenario e.g does the site require ordinary, braced or cantilevered piles?
Aesthetics and durability are key facets of decking materials. Ben Campbell, Technical Director at Abodo Wood advises that if longevity is a major concern “preservative-treated pine, preferably with a low toxicity non-arsenic treatment such as ACQ is a good option, as it comes with a durability warranty.”
Hardwood on the other hand, “is aesthetically pleasing and great in high traffic areas; but check to see if it is from a sustainable source and is FSC (Forest Stewardship Council) certified.”
The principles of construction are similar for most raised decks. Pile posts (minimum H5) are concreted into the ground with bearers (H3/H4) fixed onto the piles.
Joists then are fastened on top of the bearers; or in low-level situations, joists may be attached directly to bearers using stainless steel joist ‘hangers.’ Finally the decking boards are laid and nailed onto the joists.
Profile markers are generally set out first to create an outline of the deck.
Stringlines are attached to these and where applicable to existing structures, to achieve a building level across the entire deck space.
The secret to deck building is maintaining consistent levels and ensuring it is squared off against any existing structures, to achieve a building level across the entire deck space.
The secret to deck building is maintaining consistent levels and ensuring it is squared off against any existing structures. Decks can run up to a house but unless cantilevered, should not be attached to a house.
Pile hole depth should be 450mm deep (or until you hit firm ground) and 300mm square.
The spacing of the joists and the size of the bearer will determine the distance between each pile.
A 100mm base course of concrete is poured in each hole and left to dry.
This forms a solid platform for the pile post to sit on.
Once the concrete is dried, the bracing is removed and post heights are measured and marked with straight edge and level to achieve desired post height.
Trim posts with a handsaw or circular saw. Bearers must be laid in straight lines on edge and run continuous over two or more spans ie. Two pile posts.
If, when placing bearers on piles, the piles are wider than bearers then it is a good idea to place and mark your bearer position then cut a 45 degree angle from the surplus edge to ensure that water does not sit on pile.
On low level decks, fit joists inside the bearers as opposed to on top, attach using stainless steel joist hangers.
Bearer edges are governed by string lines and nailed into piles, two nails per side per post with two nails at each end.
A stainless steel ‘twisty’ or bearer-to-pile fixer is then fitted at bearer ends.
If a deck requires a handrail, then consider factoring in extra length pile posts on the deck perimeter that requires the handrail, and cut later to correct rail height. Check the building code for correct use of balustrades and barrier options, which can include timber, glass and aluminium.
Joist spacing is determined by the size of decking boards. Eg. For 21mm thick decking, ideally 400mm or 450mm centres maximum between joists. For thicker decking eg. 32 mm maximum 600 mm centres.
To enhance life span and performance of timber decking, pre-coat the deck surface boards on all ends and sides with a wood oil or similar.
This will reduce the damaging effects of rain and UVs that can cause colour change, swelling, shrinkage and cupping.
Always use premium grade decking to reduce the likelihood of knots.
Layout the decking boards and stagger the joints to avoid creating an obvious pattern.
Cut ends so that they finish centre of the joist. Allow a 2mm gap between boards.
Decking should be installed methodically starting at one end for each row.
To keep rows straight, a stringline can be used as a guide when laying up each deck board.
Sealing boards ends with coating or end seal preservative is particularly important, as this area has high risk of decay.
Gaps in a deck are important for water run-off, airflow and to accommodate board movement.
The gap should be determined according to the type of decking timber being used. For wet-treated pine, ‘green’ timber and some hardwoods use 2-3mm spacing between each board. In this case a nail can be used as a spacer between each decking board to give the required gap. For kiln-dried timber, leave a wider gap up to 6mm to allow for expansion.
Allow a 12mm gap where decking meets exterior walls. The stepdown from door level should be no less than 50mm to prevent rain entry. If it is to be a slatted timber deck, no stepdown is required, provided that there is a gap between the first slat and the house.
Pine decking can be nailed but hardwood decking requires pre-drilling of nail holes. Drill holes at an angle for better nail grip.
Use annular groove nails or stainless steel screws to fasten the boards ensuring the nail or screw head is countersunk below the deck surface. Screws are recommended for 140mm wide boards.
Tip: Prior to installation, Abodo’s Ben Campbell suggests: “Ensure all decking boards are kept dry, out of the weather or under plastic wrap, elevated off the ground. A professional will know where to get wrap for your deck. For non-kiln dried ‘wet’ or high moisture content timber, place thin timber ‘fillets’ between each row of boards. This allows the timber to season and will lessen the risk of unexpected movement once installed.”
This article by Jason Burgess featured on page 108 of Issue 015 of New Zealand Renovate Magazine. New Zealand's first and only magazine solely dedicated to home renovations.
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