[aw1621107]

Yeah, density was the main concern that led me to make my original comment in this thread. I was thinking of a more suburban setting when I wrote the comment you're responding to, but you do have a point (unless local zoning laws allow septic drainage fields to be used for other things, but that I know too little about). If you can't build on top of drainage fields or dual-purpose them, then you'll need to sacrifice some building space, which isn't optimal from a make-the-most-of-a-land-parcel view.