I know you feel the same way I do about this, and maybe this isn't the right spot for the debate, but what the heck since I'm typing and its a bit of a hobby horse for me....the standard is based on a very poor understanding of the biology of trees, and specifically the action and impact of root, it is based almost slavishly on the British standard which has the same idiotic base line of 1.5 x the height of the tree as the preferred distance for trees from building foundations.
We have a professional soil engineers and geotechs who make a very good living out of investigations and reports on the nature of soils in any particular area, where buidlings already exist or where buildings are planned to be built. Now to this fine body of men and women trees seem to be a total anathema, the existing standard along with local and state building regs don't help so instead of gradually getting more trees (properly) retained on new sites, and existing trees (properly) managed on existing sites we still seem to be in the trap of painting trees as the bad guys.
Trees can and do move vast amounts of water in the soil every day, but we need to recognise that movement is not simply one way (evapotranspiration) trees also lift vast quantities of water from lower in the soil profile to upper protions of the profile. Moisture gradients in the soil also lead to changes in localised moisture content....drying soils pull moisture from adjacent areas with greater moisture in other words..without the help of any vegetation.
The impact of altered relative moisture levels in a volume of soil is dependant on numerous factors previously mentioned in this thread,....and the impact that these soil changes have on buildings is also dependant on the nature of the civil works undertaken during intial subdivision and the foundations for that building.
So what am I getting at? The Goode ruling based on the evidence from the transcript is bad in so many ways, it reflects some of the fundemental misunderstandings that persist about tree roots and building movements. I'm not saying trees are never a major cause of soil volume alterations and resultant building damage...that would be silly...however I do understand enough about soil physics and chemistry to know that this simplistic model that underlies the current standards is shifting both the blame and the responsibility for subsidence from the people who alter the structure of the soil profile so fundamentally to trees that more often than not were there long before bulding on the site was even considered.
Good quality, properly installed moisture barriers (note not root barriers) have a real role in this area I think. Surround the foundations of a building by such barriers to a depth 1-2m below the excavation depth and you will effectively isolate the sub soil profile from aterations in relative moisture levels. The impact of the original cut and/or fill process and the thermal mass fluctuations created by the building will have an impact on the soil and its volume and therefore over time there will still be some buildings that still have cracking, and shortened service life span as a result.....some experts would still blame the tree 15m away in the neighbours yard for that, and if you had the same commissioner as the Goode case residing well bad luck tree.....
__________________ Sean  Trees are poems that earth writes upon the sky,
We fell them down and turn them into paper,
That we may record our emptiness.
- Kahlil Gibran
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