One disadvantage of a slate roof is that it can have a hefty upfront cost. But its advantages can more than make up for this. Slate-roofed houses offer greater curb appeal, extreme durability and can add value to your home. While it can be costly to have installed or repaired, a well-made slate roof can last an average of 75 to 200 years for hard slate, and 50 to 125 years for soft slate.