The frequency of roof replacement depends on several factors, including the type of roofing material and local weather conditions. Generally, asphalt shingle roofs need replacement every 15-20 years, metal roofs can last 40-70 years, while flat roofs may require replacement every 10-15 years. Keeping an eye out for signs of roof damage, such as missing shingles or leaks, can help determine when a new roof installation is needed.