Polystyrene, Rebar, and Concrete

The main floor of our new addition is a suspended concrete slab (i.e., a slab that is not in direct contact with the ground.) We are using the LiteDeck ICF system for this slab.


The LiteDeck system starts with a base layer of 6″ thick expanded polystyrene (EPS) with imbedded steel C channels (both for strength and to provide a way to screw on the basement drywall ceiling). It is shaped with a beam pocket 6″ W x 4″ H every 2′.


Then foam “top hats” (4″thick in our case) are added to deepen the integrated concrete beams to 8″ H x 6″ W.


Next is the rebar. Lots and lots of rebar: Two ¾” pieces along the bottom of each beam, two ½” pieces along the top, ½” U-shaped cross pieces to help hold the length-wise bars in place, topped with a 2′ x 2′ grid of 1/2″ to stiffen the slab.


Ready for concrete. The rebar is all wired together as a unit. The foam pedestals are for running plumbing and electric through the slab. You can also see the sole plate at the edges – the outside band is temporary bracing. The wooden box-like protrusion on the left is the where the basement stairway will go, the one on the right is for our dumbwaiter.


The result (as poured yesterday.) The slab is around 4½” thick. At the top is the vestibule, a 3-season unheated room that also serves as an airlock for the addition entryway. To the right is the cantilevered floor of the bow window.

As I type this the plumbers are here to run a new well pipe through the previously-installed conduit that runs through the foundation. Once inside, it is going to temporarily run through the dumbwaiter window and reattach to the existing house plumbing. Later, we are going to relocate all the plumbing mechanical (pressure tank, de-acidifier, water heater) into the addition’s basement mechanical room. But for now, this will keep the pipe from freezing this winter and allow us to finish back-filling around the north end of the new foundation where the well is.

Next week, the exterior wall framing should begin. The bottom of the wall will be triple-plated so that when the exterior shell, including roof, is in place we can pour the final 4″ of concrete for the final floor. Before that happens, though, I will be running the heat tubing that will end up embedded just above the middle of the 9½” thick floor slab.

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