How far apart should joists be on a deck?
The optimal spacing between decking joists depends on several factors. These include the type of decking material, the anticipated load, and local building regulations. Before beginning projects, those responsible for construction should always consult relevant regulations. However, there are also some useful general guidelines to follow.
For traditional decking materials, such as timber or composite boards, a typical maximum joist spacing of 16 inches (40.6 cm) on-centre is common. On-centre refers to the practice of measuring from the centre of one joist to the centre of the next. This spacing ensures adequate support and minimises the risk of sagging or bouncing between the joists. In some cases, you can reduce the spacing to 12 inches (30.5 cm) on-centre. This is more common for thicker or heavier decking materials and environments where the deck is expected to experience significant loads.
On the other hand, thinner or lighter decking materials, such as PVC or aluminium, may allow for wider joist spacing. In such cases, you can increase the spacing to 24 inches (61 cm) on-centre, or even higher. With premium RYNO aluminium decking joists for waterproofed balconies, terraces and roofs, the maximum spacing permitted is 80 cm or 31 inches.
The two main reference points when constructing decking are local building regulations and manufacturers’ recommendations. While general rules of thumb are helpful, manufacturers' guidelines always supersede them.