There are several North American manufacturers currently offering expanded polystyrene (EPS) panels that hold PEX, PEX-AL-PEX or PERT tubing between staggered rows of foam “nubs.” These panels are available in various thicknesses and compressive strengths to accommodate slabs in a wide range of buildings. The figure below shows a generic representation of how these panels hold tubing in heated slabs.
The concept is simple: Lay out the nominal 2-by-4-foot panels on a flat and stable base. The edges of the panels lock together to quickly form a tidy grid. Next, uncoil the PEX tubing and “walk” it into place (e.g., press it down with your shoe) between the nubs. The nubs usually allow spacing that is a multiple of 3 inches (6 inches, 9 inches, 12 inches, etc.).