u/Legitimate_Bet_7517

I am looking to replace the existing deck on the rear of my home, or somehow replace the support beams as erosion has made it somewhat unsafe. I am beginning the planning process with a family friend-someone who dos carpentry on the side. Does anyone know or have experience with doing this, or know if I will need to obtain a building permit if we completely replace the structure? I have looked around the city website but found no definitive answer. Thank you!