Let me first say that the advice you have been given by both Highclimber OR and Newt* is good and valid in relation to what maintenance costs you will face down the track with these two trees, its probably the case that the trees will cause you major problems as they grow over and into your building.
What I would like to add to the thread is that when clients recieve geotech reports in relation to movement under or around their house/building footings/foundations pointing the finger at the nearest tree I tend to be a little sceptical. I am not suggesting that youe engineer is telling fibs or that I am smarter than them, but simply this:
In the disputes I've been envolved with in this particular area of tree work...roots nuisance and damage claims...the relationship between vegetation and relative soil moisture levels, plasticity and soil suction is often presented as being simple and direct. It is niether of these things. Clients that have wished to retain trees are often prepared to have additional soil testing to determine what the physical and chemical properties of the subsoil under their buildings are, and how moisture is being altered in that environment, and what implications the alterations have for their building.
Put more simply trees do suck water (evapotranspiration) as everyone knows, but so does soil. Different soils hold onto their water with different strengths, suction in soils is measured by the pF value and (again simplifying) the suction of some soils in certain circumstances can greatly exceed the wlting point of trees. In other words you may have changes in your soils under foundations relating to varied relative soil moisture levels, these will have a relationship to the vegetation growing in the upper soil horizons, but if that relative moisture level drops below the point at which the vegetation can pull water from the soil changes in soil structure and stability after that are not connected to that process.
Yes my over simplification probably makes it sound like trees are never causally linked to sinking foundations, yes they can be, but I repeat the relationship is much more complex and important points of fact drawn from the geotech investigation need to be examined first.
