One question we frequently hear is, “Can I reuse my deck’s support system and just resurface with composite decking?” While this is alright to do on a rare occasion, it’s not usually a good idea. One of the biggest hinderances to doing this is the fact that composite decking requires specific joist spacing that is often different than what a wood deck has. Before we dive into the basics, let’s clarify. What is joist spacing?
Joist Spacing
Joists are crucial to the framework of your deck. Joists are the horizontal boards that run the length of your project and they have the important task of supporting the decking itself. Joists must be strong enough to carry the weight of the decking on top of them. Joists are most often wood or steel. This is because plastic, composite and other materials do not have the necessary strength to bear the weight of the decking.
Joist spacing is the distance between two joists. Joists are measured from the center of one joist to the center of the next. This type of measuring is called “on center”. This is different than measuring a gap from edge to edge. If you measure from the center of one joist board to the center of the next and it measures 24 inches, the joist spacing is “24 inches on center” or 24in O.C.
Why does joist spacing matter? The longevity and durability of a deck is reliant on its framework. If the joist spacing of a deck is too far apart, the decking will sag. The kinds of decking that are available for your deck have different joist spacing requirements. This is to make sure the deck framework can support the specific type of decking properly.
What is the Proper Joist Spacing for Composite Decking?
Most composite or PVC decking manufacturers require a 16” O.C. maximum. Commercial projects or decks installed at a 45 degree angle may be required to have joists that are 12” O.C. Each manufacturer specifies the joist spacing requirements in their installation instructions. It is also a good idea to check your local building codes before you begin to ensure your plan meets city or county requirements.
Some wood decks built before building codes were implemented have joists that are spaced wider than 16in O.C. For this reason among others, it is not recommended to install new composite decking over old joists. Your composite decking will sag. Installing composite decking on old joists that are spaced correctly is a possibility, but your joists will need replaced long before the life of your composite decking is done.
For more information regarding joists and joist spacing, feel free to comment below, give us a call, or send an email! We are more than happy to answer your questions.
