Dear MIXING IT:
Prep for ceramic or porcelain tile Post 3
Although it was quite short, I did answer your question on 9/29/14.
My new questions to you are: Why do you need a heated floor if the floor already has a built in radiant heating system. Do you feel that it is not enough? Radiant heat systems in slabs or mats do not make the floors a “hot plate”. They do warm, slowly, and methodically. If not, the floors would be difficult to “live on”. The same goes with the Hydronic heating systems you desire. Of course, you would save energy on the second (Hydronic) system however; you must follow certain “NTCA” rules, and your wish to raise the floor an additional 3/4” is not quite the space a Hydronic System requires.
It would raise your floor, above the original slab the thickness, the diameter of the tubing and the new “dry packed” cement floor that would encapsulate the tubing. And the “dry pack” must be higher by a minimum of ¾” above the tubing. There must also be some mortar, about ¼” under the tubing in order to encapsulate it 100%. 1/4” "dry pack"below, plus the tubing is which is usually 1/2” inside diameter, plus the thickness of the walls, usually 1/8” x 2.
Now let’s do the math:
1/4 “+ 1/8” + 1/2” + 1/8” plus 3/4” of Dry pack. Total = 1 ¾”. Of course, this does not include the thickness of the new tile which could add another ½”. In addition, the tubing must remain flat with no curls that might lift up by natural resistance when you are bending the tubing at each wall, to loop again and again until the entire floor is covered. Typically, heat tubing, as well as electric wires should be no closer and no further apart than 3” apart. You might consider less tubing coverage for more important living areas.
Since you do not wish to injure the radiant slab, you would have to be creative with galvanized half circle tubing clamps by gluing the clamps/clips with a hot glue gun to keep the tubes from lifting in the bends or anywhere. In addition you would have to do serious math in calculating the unbroken total length of the tubing required for this huge slab so you refrain from splice-joints which can be trouble waiting to happen down the (wet) road. If you can’t or do not wish to raise the floor this total height.
If there are stairs going down into a basement. The height of the first step would be lower than the others violating the minimum code variations allowed; usually 7 1/8” to 7 ½”.
The distance between the tops of all the steps combined (usually 11). If the installation is getting inspected there are no exceptions to this steadfast ruling. If it is not being inspected and you sell the home, you would have to reveal this lower first step variation in your disclosure statement to a buyer. It could “kill” a sale or cost a ton of dollars to revamp.
Lastly, is your 4 season climate. You must never turn off the Hydronic heating system in cold weather, or if you go on vacation, or some other mishap happens. A tile installation must have room to expand and contract around the perimeter, or you could have a bunch of tile “teepees”. To play it safe, in this 4 season climate, I would recommend two expansion joints, + - 13’ apart, perpendicular to the 37 ft longer length.
If you still wish to proceed after all I have said, please let me know.
Your friendly, knowledgeable, guide. Armen Tavy