The lot was heavily wooded, was predominately diabase, and had terrific Neshaminy soil, fairly unusual, as I understand for Montgomery County. The perc rate was exceptional allowing us to employ an in-ground gravity fed septic system as our property slopes a bit towards the rear. We over sized the absorption bed to support a five bedroom residence.
We strove to minimize the site disturbance to fewer than one acre as it would allow us to avoid additional regulatory over-site and was consistent with our strong desire to take as little trees down as possible.
Storm water management regulations were brutal and significantly added to the cost of the site development. Some areas of the building lot were deemed to have "steep slopes" which also had to be accounted for. In the case of storm-water management, the creation of "impervious surfaces," such as the driveway, the home and roof itself, dictates the need for offsetting their potential contribution to storm-water runoff, from a "100-year" rain-storm, with other mitigation features, such as trenches, water cisterns, and rain gardens (workshop video). While I certainly appreciated the efforts to reduce the damaging effects of poor water management, given the nature of our lot, felt that much of it was unnecessary and added an unforeseen expense to the overall project. If you suspect a challenging excavation project, try to have your excavator provide a fix-fee proposal with a rock-removal component included. We failed to do so, and got "hammered" with time-and-materials billing...a very costly mistake on our part.
As a result of regulations to minimize "steep slopes" in particular driveway access to the roadway, the house was specified to be placed two feet deeper into the ground. Unfortunately for us, that meant we had to go through a fair amount of granite "bedrock" and re-grade (ie; move a lot of dirt) at great expense. Those two additional feet quadrupled the budgeted early excavation work!
Unfortunately the initial job foreman* that we had at the time, grossly underestimated the site development work, particularly as it related to onerous storm-water management regulation. This was a harbinger of things to come.
The major lesson we learned from this experience is to thoroughly investigate and determine as best as one can, the effort that is needed to prepare a lot, especially given every increasing regulations...as site development cost-overruns alone can certainly kill an otherwise lucrative development project.
Another unforeseen cost overrun was excavation related to rock removal. We found out, the hard way, that the amount of boulders we unearthed would make Fred Flintstone blush. At the end of the project, however, we had a stunning hardscape of blue-gray ironstone.
* Note: When selecting trades, make sure theye are thoroughly vetted. In our case, unfortunately, we did not, went a lot on faith, but found that the skill-set and knowledge-base was woefully inadequate for such an ambitious undertaking, despite repeated assurances to the contrary. Make sure your trades are up to the challenge of constructing a home to Passivhaus standards, as that choice may be the most important decision that you will make. Not doing so can have consequential cost and time impacts throughout the building process, as mistakes made early are much more costly and time consuming to rectify later in the construction phase. I can not stress this point enough!