ROI here means: for every dollar you spend on a renovation, how many cents do you get back when you sell the house? A 70% ROI means a $10,000 renovation adds $7,000 to your home's value — you "lose" $3,000 from a pure financial standpoint.
Not every renovation needs a positive ROI. If you're staying in the home for 10+ years, improvements to livability (a new bathroom, better kitchen) provide years of enjoyment. The financial ROI matters most if you're renovating before selling.
Curb appeal wins — garage doors, entry doors, and siding consistently top the ROI charts because buyers form opinions before they enter the house. Functional improvements (updated bathrooms, minor kitchen refreshes) also outperform luxury additions (pools, sunrooms) which rarely recoup their cost.