What Lies Beneath: Our Homes' Foundations

There was a hot and heavy discussion over the use of insulated concrete forms a while back, where I said "with rare exceptions all foundation technologies are pretty gross, primitive and invasive and few systems tread lightly on the landscape." and the consensus of readers was "give me a break." But in fact there are lots of different ways to build that do not require such a massive intervention and disruption of our landscape. For centuries people living near water or in hot climates have built their homes on stilts, like the house in Fort Myers, Florida shown above. Stilts keep you above the flood, above the bugs, and can catch the wind. Kieran Timberlake did a lovely job with them in the Loblolly house for exactly that reason: keep above the flood plain and minimize disruption of the terrain.

Even less invasive than sonotubes with concrete are helical piles, which screw right into the ground to below the frost line or to provide sufficient anchorage, and when you are done they can screw right out again. Check them out at ::TechnoPost.

Ted Owens says "The ideal green home is one that will last for over 100 years, yet, when the time comes, will dissolve harmlessly back into the earth. Straw bale, adobe (mud bricks) and wood all meet this criteria." His foundations are rubble trench: "only the top eight or so inches are poured with concrete. The remainder of the foundation trench is filled with "rubble" that consists of 1.5 to 2-inch crushed gravel. The depth of the trench is determined by building code and must go below the frost line in your area (the depth of potential freezing of the earth). This system was used frequently by the architect Frank Lloyd Wright." and his houses are mostly still standing.


Philip Proefrock at Green Options describes an innovative system out of Pennsylvania that builds prefabricated foundation walls out of steel, insulation and a bit of concrete. the Xi wall has terrific insulating value without a lot of mass, yet you can finish it easily. Quoting Philip: Superior Walls manufactures a wall that has just 1.75" concrete (plus a bit more in vertical ribs spaced every two feet along its length). That means it is only using about 20 percent of the concrete used in a standard 8" concrete foundation wall. Superior Walls panels also incorporate rigid insulation in the panels, so that they have an R-value significantly higher than solid concrete. Furthermore, with the ribs, the panels are cast in a configuration much like stud walls. This allows finished basements to be easily constructed, and with only a little pre-manufacturing coordination, electrical and plumbing services can fairly easily be accommodated into the walls. The walls can also have additional insulation installed between the ribs, very much like stud walls."::Superior wall. PDF datasheet with great information here.

SIP manufacturer Thermapan points out that in Venice, all of the buildings are standing on piles made of wood and there is no reason not to use it for basements. If you protect wood from becoming a food source by pressure treating it, and design a proper drainage layer, it works just fine. They have developed a PWF (permanent wood foundation) SIP (structural insulated panel) with pressure treated exterior plywood, up to R-45. Over a thousand houses have been built with it. They promise the following benefits:

* Dry basements with no mustiness
* Cost equivalent to concrete
* No framing required to insulate and finish basement
* No cracking
* Fast construction – no concrete to cure

I would not normally recommend using pressure treated wood in a home, but here it is separated from the interior by a minimum of six inches of foam, so I think it less of a hazard. More Info at ::Thermapan

Then there are container based homes, trailer based homes, homes that move with the occupant, a wide range of options where we don't dig, blast or move the earth or need massive infrastructure investments for services and plumbing. Perhaps we are overly fixated with tying ourselves down in one spot and really don't need foundations at all.

Tags: Concrete