Useful life
Another name for service life — the years a system is expected to work before it needs replacing.
Useful life is the accounting and home-inspection term for the same idea as [service life](/glossary/service-life): the span of years a component is expected to remain functional before it wears out and needs replacing. You'll see it on home-inspection reports, reserve studies, and depreciation schedules — a 20-year roof has a 20-year useful life, a tank water heater roughly 10. The practical point for a homeowner is identical either way: track how far each big system is into its useful life so the eventual replacement is a planned [sinking-fund](/glossary/sinking-fund) withdrawal rather than a surprise. See the [home systems lifespan chart](/guides/home-systems-lifespan-chart) for the useful life of every major system side by side.