Our builder said we should have the septic design sorted out before getting too far into the permitting process. We assumed the installer would simply figure out the details once construction started, so this caught us off guard. The property is outside the city and has several site-specific constraints that don’t apply to our previous home. I’m trying to understand why the design document matters so much before anything is actually installed. Why is a certified septic design typically required before the permit and installation stages?