Why 1978 is the line
The United States banned lead-based residential paint in 1978, so homes built before that year are the ones federal rule treats as a lead hazard risk during renovation work. Window frames, sashes and trim are some of the most heavily painted, most frequently repainted surfaces in an older house, which makes a window job one of the more likely times that old paint gets disturbed.[1]
What the rule actually requires
The EPA's Renovation, Repair and Painting rule applies to paid work that disturbs painted surfaces in homes, child care facilities and preschools built before 1978.[1]
Anyone paid to do that work has to be certified, and that requirement reaches the firm itself, including a one-person operation, not just an individual worker. A crew member either holds certification as a certified renovator or works under the on-the-job direction of one.[1]
The rule's core idea is straightforward: certified firms are expected to follow lead-safe work practices built to keep lead dust from being created or spread during the job, protecting both the crew and the people living in the home.[1]
Who's exempt
Homeowners doing renovation work on their own owner-occupied home are generally exempt from the certification requirement. That exemption goes away if part of the property is rented out, if a child care business operates there, or if the owner buys and renovates homes for resale.[1]
In plain terms: if you're paying someone else to replace windows in a pre-1978 home you live in, the certification requirement applies to them regardless of your own exemption as the homeowner.
What this means for a window job specifically
Removing an old painted sash, cutting into painted trim, or prying out a painted frame all count as disturbing a painted surface. A full-frame replacement, which pulls the whole frame down to the rough opening, disturbs more painted surface than an insert replacement that leaves the exterior trim alone, which is one more reason the replacement method matters in an older home.
What to ask before a crew starts
Ask directly whether the firm is certified under the rule, not just whether an individual worker has taken a class somewhere. Ask who on the crew holds the certified-renovator credential and who else is working under their direction that day. Get the answer before the first window comes out, not after dust is already on the floor.
Why this is worth pressing on, not just checking a box
A certification number belongs to a firm and to specific individuals within it, not to whoever happens to show up in a branded truck. Write the number down and confirm which certified renovator is responsible for that day's crew.
Young children and pregnant women are the two groups most sensitive to lead exposure, and old window components are a frequent source because they've been painted and repainted for decades and rub against each other every time they open. Keeping dust from spreading in the first place is simpler than any cleanup that comes after.