HVAC & Mechanicals
Tightening an old house or building a tight new one means that you can't leave ventilation to random leaks anymore. You have to control it.
New energy codes are coming (very) soon; many states are jumping straight to the most aggressive one
All clothes dryers should vent directly outside.
You can control the bath fan and the light from the switch, automate with motion and sensor controls, or you can mix and match methods. You can even tinker at the switch