Strapping placed on an existing floor to create “sleeper bays” in which to run radiant tubing. Most often, 2 by 4’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 . For more information see The Suspended Slab Installation in the Installation Details section of this site.