This wooden sundeck we constructed in Durban was a low-level deck which was barely off ground level. We were taking it flush off the level of the floor in the lounge and extending it outwards into the garden. The grass was not growing properly in this area due to large trees that were creating a large shadow so the client wanted to deck it to eliminate this problem.
The biggest challenge when building a wooden deck near or on ground level is to get a support beam underneath the joists where needed. There are two methods one can use. The first is what I call the cleat and beam system whereby a beam is placed underneath the joists to give them their support. We normally use a 38 x 114 joist and a 50 x 228 beam. One needs to span the 38 x 114 to a maximum of 2m but 1.8 is preferable. So every 1.8m to 2m one needs to slot an under beam below so as to support those joists. Posts should be used every 3m on the 50 x 228 beam. With this spec one can save on timber while still providing adequate support so that the deck is structurally sound.
The problem with this system arises because if you have a 228 beam, plus a 114 joist and then a 19mm deckboard on top of that your total height needed above ground level is 361mm. If the deck is too close to ground it will mean excavating soil to be able to drop that beam down enough to still arrive at the original height of your deck. Although this is quite possible and not that too time consuming, it sometimes results in the main beam sitting in soil or it may come into contact with wet soil over time. One must therefore use at least H4 CCA Treated SA Pine as the beam and in fact that whole substructure should be H4, even though the joists aren’t in contact with soil, to ensure that no rot will occur.
The other method is to create a frame, all in the same plane using 38 x 114 and use no under beam. This will result in the deck only being 133mm in height so that no excavation will be needed in order to bring the deck up to the required height. However now that you don’t have a beam to attach posts to, you will need to attach the posts to the joists and fascia beams. Again this is not a problem, but it will require a few more posts than in the first method as you can only span your 38 x 114 to a max of 2m. Hence more posts, more concrete and more labour in digging holes.
We used the joist and beam system here as we had enough space below to set the beam without having to dig too far into wet soil. So our work was made lighter by not having to dig too many holes.
Once the substructure is up, the deckboards can go down. On this wooden deck we used 19 x 68 balau deckboards. We used two deckboards as a fascia to cover our joists and beams, filled our holes with epoxy, sanded and sealed.
For a free no obligation quote or advice on your deck or other outdoor timber construction please call us on 082 496 5444 or use the form below to contact me.