Old windows are the biggest lead hazard in a pre-1978 Rockville house

Ask most people where lead paint hides and they picture peeling walls. In the houses we test around Rockville, walls are usually the easy part. The component that fails, over and over, is the original window. If your house in Twinbrook, Lincoln Park, or the older blocks near the courthouse still has its first set of windows, those windows matter more than every wall in the building, and this guide explains why, what your options are, and what each option costs.

Why windows and not walls

Intact paint on a wall mostly just sits there. A window moves. Every time an old double hung sash slides open, painted wood rubs against painted wood, and that friction grinds old paint into dust too fine to see. The dust settles on the sill and collects in the well at the bottom of the frame, which happens to be exactly where toddlers put their hands and where a summer breeze pulls air into the room. Sills take impact too, from the sash dropping and from decades of ordinary use, so the paint there chips even when the rest of the room looks fine.

Regulators call these friction and impact surfaces, and they treat them differently from walls for good reason. You can encapsulate a wall with a special coating and be done. You cannot lawfully encapsulate the surfaces where a window rubs, because the rubbing destroys the coating and keeps producing dust underneath it.

The numbers Maryland tests against

When a Maryland rental unit is inspected at turnover, or when any lead job is checked after the work, the test is dust wipes sent to a lab. The passing standards are 10 micrograms of lead per square foot on floors, 100 on window sills, and 400 in window troughs. Those are small numbers. A sill can hold a fresh coat of paint, look spotless, and still fail, because the dust being measured is coming from the friction surfaces inside the frame, not from the surface you can see.

This is why so many landlords get stuck in a frustrating loop: clean the unit, fail the sills, clean again, squeak past, then fail again at the next turnover. The window keeps making dust between inspections. Our landlord guide walks through the full Maryland turnover cycle, and old windows are the single most common reason a unit keeps landing back in it.

Repaint it or replace it

Stabilizing the paint and cleaning thoroughly is a legitimate treatment, and on a tight budget it gets a unit through inspection. But on a window it is interim by nature. New paint on a friction surface starts wearing the day the window is first opened, and the leaded layers underneath go right back to shedding. You have bought time, usually a year or two, not a solution.

Replacement is different in kind. Pull the old sashes and frame liners, install a new vinyl or fiberglass unit, and the friction surface is gone permanently. There is no lead anywhere in the new window, nothing to monitor, and nothing to fail a future dust wipe. For a landlord, that is the difference between a recurring line item at every turnover and a one time cost. For a homeowner with young kids, it removes the main exposure route in the house rather than managing it.

What replacement costs in Montgomery County

In the quotes we see across the county, a standard vinyl replacement window runs roughly $500 to $900 per opening installed, with lead safe setup and cleanup included. Basement hoppers come in under that, bays and picture windows above it. A typical 1950s Twinbrook rambler with twelve openings lands somewhere between $7,000 and $10,000 for the whole house, and a smaller job targeting only the windows that actually failed can be a third of that.

Compare that against the treat and clean route at a few hundred dollars per window, repeated every couple of years, plus reinspection fees, and replacement usually wins on math alone within two turnovers. It also shows up in the utility bill, since the windows being replaced are usually single pane. Our cost guide has the full pricing picture for lead work in this market if you want to see where window jobs sit inside it.

The rules that apply to the work

Window replacement in a pre-1978 house is regulated work. Any contractor doing it must be EPA certified under the Renovation, Repair and Painting rule, and the small job exemption that covers minor repairs never applies to window replacement, no matter how few windows are involved. That means plastic containment, HEPA cleanup, and documented practices on every job. A window contractor who shrugs at the question is telling you the dust from your old sashes will end up in your yard and your carpet.

Owner occupants doing their own work are exempt from the federal rule on paper. The dust is not exempt. Dry scraping or power sanding old sashes inside your own house is how a family with no prior lead problem ends up with one, so if you take the do it yourself route, wet methods, plastic sheeting, and a HEPA vacuum are the minimum.

Decide window by window, not house by house

The mistake we see most is treating the house as one decision. It is not. Plenty of Rockville houses have a mix: original windows on the second floor, replacements from a 1990s remodel on the first. An XRF test reads each window in about a minute, without damaging anything, and tells you exactly which openings have lead and which are already fine. Test results turn a scary whole house estimate into a short list.

That is how we run it: test first, then a written quote listing each window with its reading and its price, then containment, replacement, and clearance dust wipes at the end so you hold lab proof the job is done. We do this work across Montgomery County, and if the testing shows your windows are already clean, that is the whole bill.