How to Build a Deck

Adding a deck on to a house can add valuable outdoor and entertaining areas with the ability to extend a room. A deck can be built on to the house and integrated around trees or to surround a pool. If the ground falls away from the house it is a simple matter of lengthening the posts so that the deck is level with the house floor. There is no need to level the site or to remove trees as long as the trees are strong and healthy.

Setting out the Deck

Trees can be left be part of the design of the deck and can provide shade and cover. Many times a tree is not part of the design and a cover is to be built on top of the deck. If this is the case the posts around the deck should be installed at the full height of the pergola or awning roof. This way the posts that hold up the deck also hold up the pergola roof. Check span tables to make sure your post are strong enough to hold both the deck and the pergola roof.

Using a string line and a laser level or automatic level (dumpy level) set the height of the deck. Set the finished height of the deck level with the floor of the house or at your desired height. Mark along the house and check the level that it is completely straight and level. Then measure down to mark the bottom of the bearer. For example:

  • 20mm Decking board
  • 140mm joist
  • 140mm bear

In this example you will need to measure down 300mm from the finished deck floor level mark and mark the wall again. This measurement will vary with the size of your deck and the different sized timber you need. This measure down mark is the bottom of your bearer or you can just measure down 160mm for the top of the bearer. Whatever method you use you can now start to set your bearers and posts to the correct height. Span tables will be able to show you the correct spacing for your beakers which will depend on the size and span of your deck.

Choosing your timber


If you can afford it class 1 hardwood looks the best and is the most durable or H4 treated pine. Both these timbers can be used in ground; although I believe it is always best to use hot dipped galvanized strips in ground and the timber used above ground for maximum durability.


Joists can be class 1 or 2 hardwood or H3 treated pine for above ground use. Most joists will not be seen so as long as it is durable hardwood or treated pine will not change the look of the deck.

Decking timbers

Hardwood decking timber looks the best and is the most durable. There is no need to stain the timber just coat it in water based or oil based decking sealer. Treated pine can be used and stained or painted to the desired color however they generally do not look as good as the natural colors found in hardwood. Although treated pine is cheaper than hardwood and is a valid choice for decking boards.

Decking tips

  • Always use hot dipped galvanized or stainless steel fittings and fittings.
  • If your deck is near the coast 316 stainless fitting are a must.
  • All decks with the floor height above 600mm must have a balustrade of 1000mm or 1 meter high.
  • Steps should be strong and be wide enough for two to past each other.
  • Before you start, check your deck with council.
  • Make sure you have a clear plan and drawings.
  • If you are building around trees leave room for them to grow.
  • Always check you have the correct sized timber and the deck is very strong.