This is a great question, Mim.
TimberTech deck planks cannot be installed directly over an existing surface. However, with the use of a minimum of a 1-1/2” sleeper system supported by and connected to the substructure (concrete), TimberTech planks may be utilized in this application. Be sure to have provisions for drainage in place, because the supporting sleeper system cannot impede drainage. The sleeper system should be set to a maximum span for the specific decking profile of choice. As with any project, we recommend you review local building codes and if needed, consult a contractor prior to installation. For more information – check out our decking install guide.