Pros & Cons: SLABS

November 1:  My plan calls for a slab-on-stem-wall home, not a framed-floor-on-basement home. It’s an unusual choice for our corner of the Midwest, and a little risky from a re-sale point of view. From a low-carbon-footprint and affordability point of view, it makes perfect sense.

Concrete is a high embodied energy material. That means a lot of energy has to be expended to quarry the materials, transport them, crush & cook them, and deliver the mix to the building site. The less concrete used, the better for the environment.

My stem wall is 4′ high, so compared to a basement with an 8′ ceiling, it uses half the amount of concrete. I considered a few alternatives: Insulated Concrete Forms (ICF) or Durisol block—both of which use less concrete, and a Frost Protected Shallow Foundation (FPSF) which uses even less. These alternatives aren’t exotic, but require some amount of special order and special expertise. One of my goals for POEMHOMES is to make choices that are easily replicated. For my first go at general contracting, I need things to be somewhat “plug & play”.  A 4′ stem wall is familiar to the trades—and manageable by me.

Having no basement saves money because there’s no stairway and no framed floor. There’s no need for drain tile, damp proofing, and a sump pump (with backup power). Potential leaks or flooding are eliminated—-and so too worries about mold and mildew. An insulated slab stays high and dry and the hard trowel finish becomes the finish floor. When the sun shines, it soaks up heat energy—releasing it back into the rooms as temperatures cool. A slab can be set on or close to ground level, for easy accessibility. I’ll have one 8” step up—not the usual 20” or more necessary in conventionally framed floors.

Of course there are disadvantages and trade-offs. With a basement, mechanicals are easy to install and switch out. Storage is plentiful, you can build out a rec room or additional bedroom, and you’ve more-or-less got a tornado shelter. A slab commits you to a smaller footprint (sans future addition). You have to find space for a mechanical room and plan ahead for plumbing, electrical, and HVAC runs.

My design has a small walk-in-closet on the main floor for the grinder pump, water softener, and hot water heater. Above is an attic of sorts, for the HRV (heat recovery ventilator) and the ASHP (air source heat pump). Electrical runs and ductwork will be routed across the length of the house above the living areas.

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Notice in the illustration above how the slab rests on a 4″ layer of foam (blue), which overlays sand fill (brown).  It’s a lot of fill.  The lot looks flat, but it’s not.

A tornado shelter—if done to FEMA standards—is a major expense. I’ve wrestled with this, and am satisfied I have a good-enough answer. See future posts for more.

Slabs may not be most people’s preference, but if the Village of Spring Green is going to grow they are inevitable. People here remember the “Flood of ’08”. Rising groundwater—from record-breaking rain the previous summer, record-breaking snowfall that winter, and above-average rain that spring—flooded basements and sent homeowners packing. A whole subdivision—-just a mile north of me—was razed. To forestall more financial ruin, the Village passed an ordinance—affecting lots just a stone’s throw from mine—that restrict basements to storage and utility only—-no “below grade living space”. Other lots require slabs. My goal is to show how liveable, pleasant, and affordable a slab home can be.

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