As I already said, US patent law strongly discourages people from "mak[ing] sure [they] don't violate others' IP".  When you write software, you pretty much have to ignore patents and deal with any resulting consequences should they materialize.

Your house analogy implies that Linux (and/or Linus) knowingly stole code (lumber) from somebody (SCO).  The validity of that claim is for the courts to sort out, but in any case it is not the same as unknowingly infringing on Angel patent(s).