Foundation & Concrete

Early-on we made a decision to keep our existing house foundation (pier & beam), but tear out the old garage foundation and create a new one (slab).

Because our house is on a left-to-right slope, the garage foundation challenges were somewhat unique.  A mistake was made by not getting a detailed topographical done on the property, and when we started the excavation for the garage the retaining wall ended up about 2+ feet higher than it was supposed to (note:  added cost).

We also had a set-back issue – the city looked at the courtyard retaining wall design and called it OK.  Then when the concrete forms were created the city changed its mind.  It was because they originally thought that there were two different structures:  the garage walls and the courtyard walls.  Turns out, the engineer made all of the walls fully integrated.  Long story short:  we had to shorten our courtyard a couple of feet (luckily the design still worked to allow me an outdoor bar area!).

Our foundation & concrete work features four Green elements:

  • Recycling – we recycled all of the existing concrete, including the foundation under the old garage.  Either we’re tearing out the concrete and sending it to a recycler to make gravel, or we’re using the recycled concrete slabs in the landscape design for terracing (remember our property slope issue).  None of our concrete will end up in a landfill.
  • Reuse – as noted above, we reused the house’s foundation and piers.  We had to add a front and back porch structure and a couple of new piers, but the existing foundation was deemed to be more than adequate for the new home.
  • Durability – LEED gives extra points for durability features.  Our foundation was engineered with more steel structural support than typical.  The rebar support was created at 8″ on center rather than the typical 10-12″ on center.
  • Content – we used 30% fly ash concrete.  Fly ash is a residue created from burning coal.  It’s either left to drift into the atmosphere as pollution or it’s captured.  However, 65% of what is captured ends up in landfills.  To learn more about 30% fly ash concrete and its ability to increase the strength of concrete and to help the environment, visit this link.

And finally, the last question:  how much extra did the Green elements cost?  The fly ash concrete is probably a 10% surcharge – which makes me wonder why every house doesn’t use this type of concrete.  The use of more steel reinforcements probably increased our metal cost by about 15% (non-inclusive of the higher price of steel).

Our overall foundation work went over budget significantly, but mostly due to the mistake in not understanding the extent of the foundation work required, the rework due to the city’s overly-zealous inspectors (and I say that mostly tongue-in-cheek), and the skyrocketing cost of metal caused by higher fuel prices to haul it.