Once you have a solid set of instructions and sound decking plans to work with, building a deck need not be a difficult process, even for an inexperienced carpenter.
The technique I explain in this article is a professional deck installation method which can be used for deck heights between 350mm to 1.8m above ground level.
Inserting timber posts
1. Draw up your deck plan on paper first. (If you are stuck for ideas, there are plenty of resources online that supply deck plans) To be able to properly draw your deck design you will need to work out exactly where to position your posts and your purlin structure and joists.
2. Lay out the perimeter of your deck with string or line. If you are building a square deck, be sure to check diagonal measurements.
3. Mark the positions of your posts using an ink marker or chalk. Your posts should be approximately 1.5 – 1.8m apart.
4. Now dig the holes for your posts going approximately 400mm deep. Insert your posts into the holes, lining them up and bracing them, making sure that the bracing will hold them in place while the concrete sets. The post will be cut later so it doesn’t matter how high they extend out of the ground.
5. Ensure your posts are plumb (level in the vertical plane.)
6. Pour some ready made concrete into the holes, filling them to the top.
7. Allow the concrete to set for 48 hours before pulling the timber bracing off and cleaning any concrete off the posts.
Purlins are horizontal beams running along the length of your deck to support the decking boards. The purlins are supported along their lengths by posts.
The purlin structure will run the same direction as the finished deck boards, which is normally parallel to the house / patio doors.
Decide what level you want your finished decking to be, then work out your post heights from this – calculate backwards.
Use a self-levelling laser level on a tripod to set levels over a large deck. Ensure any laser-level you use has been calibrated within the last 6 months.
Bolt 6″ x 2″ planks on their edge to either side of the posts, stagger your joists so that you don’t end up with two joints on the same post. (Timber locks can be used instead of bolts as they are just as strong and much faster to use. Pre-drill the 6″ x 2″ timber first, insert at least two bolts or timber locks.
As an extra reinforcement insert a 4″ x 2″ dwarf leg between the 6″ x 2″ and the concrete base and attach it to the post with screws or timber locks. This will ensure that your substructure will last 20 years plus. This will transfer the load to the ground.
To create a water run-off you must create a slight slope on your decking. We will aim for a slope of about 1 in a 100. To achieve this we will set our levels using builders line. 50mm in 4.8m will create a 1 in 100 slope.
Dwarf legs can be used to reinforce the purlins. Once the purlins are positioned and bolted / timberlocked the purlin structure is now complete.
Setting out the joists is now straight forward (ensure that the joists 4″ x 2″ (or 5 6″ x 2″) are regularised (that the joists are actually of same dimensions) – this is very important otherwise the deck could be uneven.)
Lay your joists out on top of the purlins at 90° to the purlin structure. The joists must be spaced at 250mm (10″) apart. The joists can be fixed to the purlin structure using 80mm stainless steel screws or 3″ galvinised nails. This should ensure the strength and durability for your decking to last two decades of use.
Now all that remains to be done is to insert bridging pieces between the joists to strengthen the joist structure. Use 10″ (250mm) pieces to do this.
Bridging pieces 250mm (10″) should be inserted between the joists to ensure a rigid, strong joist structure.