Viega Rapid Grid
A recent radiant floor install was the perfect opportunity to try out the high impact polystyrene foam board system for my first time. Rapid Grid is a 2’x4′ interlocking foam board system with raised knobs that hold 3/8″-5/8″ PEX tubing with minimal use of staples or the need for wire tying to grid work.
Typically my radiant floor installs consist of using 2-1/2″ foam board staples to attach 1/2″ oxygen barrier tubing directly to 2″-25psi 4’x8′ foam board insulation. Normally the insulation is installed by the general contractor or another sub but I have done it many times so installing the Rapid Grid was useful for comparison purposes.
Our building code requires a vapor barrier, regardless of the insulation system used but the typical 4’x8′ foam board also requires a poly seam tape coverage on all joints. That’s the main difference I took away from the actual laying of the Rapid Grid. The Rapid Grid has a directional tongue and groove type of system that joins each piece to another. This overlapping joint system negates the need for sealing the seams and also holds the insulation together well.
I did go over each loop and staple where I felt needed, especially on each loop end. Staples are not entirely eliminated but mostly due to the memory in coiled PEX tubing. The tubing is held very well withing the Rapid Grid knobs however its not perfect. Watch close in the video and you’ll see very brief spots where I stapled in between loop runs.
In the end, after a cost comparison using current pricing available for 4’x8′ 25psi foam insulation board and my current pricing from a local supplier, Rapid Grid is higher price per sq. ft.
Given the labor savings, this system was installed in just over 3.5 hours verses an average 4.5-5 hours of my typical installs this size, I can see the Rapid Grid being competitive when typical foam board market pricing is elevated. This floor is just under 3K sq ft, smaller projects like slab on grade additions could be an excellent application.