The Slab

Yesterday the slab was poured for the first floor.  As you may or may not have known, the home is designed as slab-on-grade construction.  However, the slab has been slightly lifted out of the ground to avoid the slab appearing to be right at grade from the front entrance.  Further, you will notice in the photos that the slab at the front entry is lifted 8″ higher than the rest of the first floor to give that space a bit of definition and also allow for a nice transition from interior to exterior.

The final finish of the slab is to remain it’s natural gray tone, simply sealed with the soy-base sealer Acri-Soy.

In terms of the slab itself, we did some research into proper insulation for both the slab itself and also the foundation walls.  We made some changes along the way and have learned some things during the process as well.  We feel the end solution will perform much better than our initial details had shown.  We wanted to make sure the slab was properly insulated but still stayed within a reasonable budget.  The initial thought, before additional research, was to use 2″ rigid insulation up the interior face of the foundation walls and then to extend it parallel to the slab 2′ in around the entire perimeter.

There were two places in particular, however, that we modified this initial insulation strategy.  We decided, after some research and recommendations, that it would be beneficial and more efficient to provide some sub-slab insulation under the entire slab…as opposed to simply this 2′ band around the perimeter.  As a result, we continued the rigid insulation under the entire slab which will provide a greater insulation value and allow the floors to stay warmer in the winter.

The second modification was to address the issue of the thermal bridge between the foundation block and the slab itself.  Originally, and what is typical in many slab-on-grade details, is to simply allow for the slab and the foundation to essentially butt up directly to one another…with some sort of expansion joint.  This, however, creates a thermal bridge and can cause a temperature differential between the edge of the slab and the underside of the slab.  As a result of this bridge, we placed tapered 2″ rigid insulation between these two elements, eliminating this thermal bridge.  The reasoning for the tapering was to allow the slab pour to extend completely to the interior wall edge.  Below is an illustration found during our research which demonstrates this detail (ignore the radiant heating aspect though):

We are very pleased with the results of the pour and can begin to envision the living spaces a little more.  In other news, we received the money from the city today for the manufacturing of the SIPs (Structural Insulated Panels).  So, we should be moving forward with the walls as final shop drawings come in the near future.  Can’t wait till we see some walls going up on site!


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