Definition
A provision allowing existing non-code-compliant elements to remain in place because they predate current requirements. Grandfathered status doesn't apply if systems are modified or replaced.
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Building codes change over time; existing homes may not comply with new standards. Grandfathered provisions allow old systems (knob-and-tube wiring, outdated electrical panels) to remain if not modified. However, repairs, replacements, or modifications must meet current code. Adding a bathroom requires GFCI outlets; replacing a furnace requires upgraded venting. Grandfathered status is jurisdiction-specific and varies by application.
Pro Tip
Understand that grandfathered systems may be outdated but legal. Upgrades will be required for renovations.
Example
An older home had ungrounded two-prong outlets throughout, which would be code violations if newly installed. Because the outlets predated current codes, they were grandfathered. However, if outlets were replaced, new outlets must be grounded three-prong type.