Strapping placed on an existing floor to create “sleeper bays” in which to run radiant tubing. Most often, 2X4’s laying flat, 16″ on center, act as the best sleepers. They raise the floor 1 1/2″ and allow adequate room for even the largest tubing. Sand or concrete is generally placed over the tubing, between the sleepers, and the sleepers are then used 1) to screed across in the case of a concrete floor, or 2) for nailing down the finished floor.