Calculate the amount of timber that you need. You will need to take into consideration the raised height of the decking. Example:
The decking is raised a ¼ meter above ground level. With a 4"x4" decking post of length 1.8m - set at 4 corners and 2 intersects you will need.
Lets assume you're using a 4x4" - 1.8m long fence post. Their sturdy and long lasting. In the above example, 1 set post is going to be of length 0.35m. There are 6 total meaning:
6 x 0.35m = 2.1m total length needed. Fence post = 1.8m
2.1m / 1.8m = 1.16 Fence posts.
Now you need to calculate the timber needed for the perimeter of the decking frame. Its pretty simple. In this example were going to assume that you're building a rectangular decking.
The next step is measuring for joists. This can get quite complicated, but for the sake of simplicity we'll continue with our rectangular example. We'll mention laying joists later in the article, but an important point which needs to be considered here is the joist spacing. If your using 2"x4" x 3.6m timber for your joists then the recommended spacing between joists is 12-16 inches.
Here is a recommended deck spacing guide from decks.com
Next up is measuring the amount of decking boards you will need. Staying with the rectangular example, we will calculate the amount of decking boards needed from the set area formula Area = Length x Breadth.
2) Preparing the Ground:
Using pegs and string (Taught string which gives a straight line) set out the deckings perimeter. Once done clear all the grass, plants and loose turf from the area while patting down and compacting the residual underlying soil.
Lay a form of weed control fabric over the cleared area to prevent weeds growing up through the deck. Weighing down the fabric will ensure it is held in place. Hint, tent hooks are useful for securing the weed control fabric.
The framework for a decking should be laid onto concrete foundations. The supporting decking posts need to be mounted on a concrete area or set in dug concrete foundations. If digging foundations dig a hole to suit the dimensions of the post, pour in the concerete and insert post. Allow to dry. Ensure the post is level during setting. Check with a spirit level.
Another alternative is to lay concrete slabs in place to where the concrete posts will be. An idea is to lay them in a patterned design approximately 140cm apart from each other. If you are choosing this method then it is a good idea to lay squares of bitumen or rubber on the slabs to give both grip and shock absorption between the decking frame and concrete slabs.
3) Building the Framework
Start by laying your deck posts either on your concrete slabs or if you have already set them in a concerete foundation. From there on the outer frame of the post (outer facing side of the deck posts) line up your decking beams ensuring that they are in line / level. Check this with a spirit level. Your beams will form the perimeter of the decking frame. Screw in the beams using appropraite length wood screws.
Once you have constructed your frames perimeter with the posts and beams now we're going to start attaching the joists.
Depending on the size of your decking will depend on whether to lay joists in a single direction OR to form a cross section of joists. In this example were going to simply lay in one direction. So cut the joists to appropriate size. This can be done with a hand saw or for efficiency if you have a circular saw it will make the job alot faster.
If you are attaching the decking to your house ensure to use washers and leave a 10mm gap. You will need masonry screws to affix to a concrete or brick wall. Be careful not so splt the wood however. It is advisable to pre dril your screw holes in this instance. Ensure that the framework is sloping slightly away from the house also to prevent water running into the house.
The next step is to lay the joists. Lay the joists in one direction ensuring that they are at a right angle to the decking beams. Space the joists at approximately 12" intervals and screw to the frame using wood screws. This can be done directly through the wood or additionally use joist hangars to prevent cracking and provide more support.
You can also use some wood glue for additional support. For even more support add "noggins" these are short pieces of wood that attach BETWEEN JOISTS.
4) Fixing the Deck Boards
Once all the joists are in place the decking framework should be completely rigid. If the frame does need feel rigid enough to support the boards add in extra joists or noggins.
Boards MUST be layed horizontally or in the oppossite direction to the joists. This allows you to make a solid center fixing of the board and joist.
Lay a couple of boards at a time allowing about 10mm between them.This allows for expansion of the wood during hot weather as well as providing ventillation to prevent against rot etc. You can get specialsed decking screws or galvanised screws to attach the decking boards. Use either or because they don't rust and having rusted screws takes away from the look of your decking.
As mentioned before it is advisable to pre-drill screw holes to prevent cracking. Start by fixing the decking boards at either end of the beam and then proceed to center fixings. Ensure the decking board ends are in line; for cosmetic purposes. REMEMBER TO JOIN BOARDS OVER THE JOISTS. This will cover the joist as well as give a secure center fixing.