difference between new roof and replacement

https://list-wiki.win/index.php/New_Construction_vs_Replacement:_Choosing_the_Right_Roof_for_Your_Austin_Home

A new roof is installed on a new building or structure where none existed before, while a replacement roof involves removing an old roof on an existing structure and putting on a new one. The main difference is the presence of an existing roofing system; replacements require tearing off old layers, adding underlayment, and ensuring the deck is ready, whereas new roofs are built on a clean slate. Both need proper installation, but replacements often involve more labor and disposal costs.