Construction Design-Concrete-less Slab Foundation

A few weeks ago work began on a new home that I helped to design.  I’m not the general contractor on this project, more of a consultant conducting testing and assuring the building science side of the project goes as planned.  This posting will be the first of several about this build.

I first saw this unique floor system on the JLC website, designed by architect Steven Baczek.  The foundation features insulated concrete forms (ICF) on a 12″ x 24″ poured footing.  The soil is carefully backfilled and compacted in lifts of no more than 6″.  We used clean pit-run sand for the backfill.  The top 3″-4″ of material is rock fines, a local material sometimes used for the top course of a driveway.  It packs harder than the sand.

Many single level homes in my area are being built with frost protected foundations, read more about this type of foundation here.  The design for this home requires a full frost footing, five foot deep for my climate zone, which the exterior walls of the home will sit on.  The entire home will be built and dried in without the floor system in place.  More on the floor system later, first, some photos showing the progression of the foundation.

Foundation excavation. That’s my dad in the foreground. 72 and still operating the excavator.
Insulated concrete forms (ICF) are in place, backfill has begun. Part of the process includes wetting the sand to assure good compaction.
Compaction was completed in six inch lifts and mechanically rolled.
Sand backfill is complete.
Rock fines are placed but not compacted. Final grading and compaction will take place after dry-in and plumbing rough-in.

The floor system is part of what makes this home unique.  After the below grade plumbing is complete, the rock fines will be graded and compacted.  A 6 mil vapor barrier will be placed on top of the rock fines to keep any ground moisture out of the floor assembly.  Two layers of expanded polystyrene foam (EPS) are placed above the vapor barrier and two layers of Advantech flooring sit on top of the EPS foam.  This type of flooring system will be warm without in-floor heat and any floor covering can be installed over the Advantech flooring.

The one concern with this type of floor system is what happens if a plumbing leak should flood the home.  We don’t want an unintended indoor swimming pool.  There will be disaster floor drains placed in the mechanical/laundry room, kitchen, and bathroom, basically any room that has water.

With the foundation work complete, next step is to start building the walls.  The drawing at the top of the posting shows some of the details.  I will be posting more as the home’s build progresses.  Stay tuned.

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