What Lies Beneath: Our Homes' Foundations
by Lloyd Alter, Toronto 
on 04.10.07
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.
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This has been a good discussion so far. As I said at the outset, I don't think we are that far apart (if at all) in our respective views.
However, I do disagree with the sentiment of the ideal building dissolving back into the earth in 100 years. There are some places where that is preferable, but that cannot be the standard for all construction. A lot of building is, by its nature very long lasting. I've lived in a building that was more than 100 years old (though with more recent upgrades). A good building can last for centuries and serve its purpose well.
Unless you think people are going away sometime soon, shelter is going to remain a necessity. Having buildings that continue to stand and serve a purpose (even if it isn't the purpose for which they were initially constructed) is sometimes the greener approach.
I saw them use the Superior Walls or similar product on This Old House for a project. They even were able to tie into an existing foundation so it could even be used to add on to an existing structure. The nice thing about it besides the savings in materials was the speed at which it went in. The whole thing came on a truck and was craned into place in a day. The negative that I can see is the transportation of the panels from the plant to the jobsite.
Traditional foundation construcion would have been concrete forms, maybe some rebar , a pumper truck, and several cement trucks. The wall would be 8-12" thick using a lot of concrete.
Just for clarity - "pressure treated" means a solution of copper chrome and arsenic is driven into the wood under pressure, doesn't it?
LA: yes it does, which is why I do not like it very much and certainly not anywhere where it is in contact with anyone, like decks or handrails where is is commonly used. buried in a foundation, I think one can say that it is worth considering as an alternative to eight inches of concrete when it is on the outside of the wall.
And in many cases arsenic is now banned, although I do not know if that is the case for this particular use/
And don't forget PIN Foundations from Rick Gagliano which are one of the least invasive of all. They are now beginning to use them on houses after 20+ years for decks, foot bridges, etc.
Philip is right but the durability of a house here is somewhat a culture thing. In our culture much of your self esteem and worth is wrapped up in showing what you accumlate and the bigger the house--the higher your score. To build houses to last longer with less interm maintainence means building them better which equals a smaller house for the same cost--tough sell in our culture.
I'd not heard of PIN foundations until the reference above. I found the website and they look excellent. I think I'll use them on the new outbuilding on my property.
This a great article. However, it's pretty funny for the SIP manufacturer to point out that Venice is also built on wood and then promise a dry basement. Last time I checked Venice is rapidly sinking into the ocean and floods daily, their marketing group might want to rethink that one:)
All well and good. But I'm finding one significant problem with alternative foundations. Bank financing/mortgage generally look for traditional (stemwall) type foundation for loan approval; state building code approval often likewise. I'm trying to finance green casita style factory built manufactured home (16x40) on sonotube, Arizona desert locale. Contractors are negative--promote stemwall solution. I even researched/wanted to do ERBS (earthquake resistant bracing system). Contractors said there wasn't enough money installing such a simple and highly successful system. Solution is to overcharge to install ERBS system--promote stemwall alternative citing state recommendations. I just want a good inexpensive/simple solution--plus leave site as natural as possible. Any suggestions? Maybe take the project to an architect/contractor who can cut thru red tape and bs? Sonotube seems like decent solution...