According to an article in the Baltimore Brew, two new developments in science and law are challenging the rules set by historic districts on when window replacements are acceptable. These two developments are:

Baltimore's Commission for Historical and Architectural Preservation (CHAP) is being challenged to revisit rules that require landlords and developers in the city's historic districts to repair rather than replace windows. The Commission's standing policy requires owners of properties within the historic district to strip the paint off windows in order to retain the original frames on the building’s front facade. But one property developer, Three Cowboys Holding Co., has argued that high levels of lead paint found in the windows of an 1840's Georgian mansion it is renovating will expose it to potential lawsuits by tenants moving into the building, and wishes to replace the windows entirely. 

The Coalition to End Childhood Lead Poisoning is lining up to support the developer's challenge, asking the commission "to permit developers to use substitute windows – made of wood, metal or even vinyl – on buildings that test high for lead paint." And the Bolton Hill Architectural Review Committee advocates that CHAP “is not a health and safety agency” and should not get into the business of deciding when and where replacement windows are better than stripping away the old paint.

The case is expected to affect communities throughout the Baltimore area, and could set a precedant for historic districts nationwide.  Read more.

Keep in mind that even if historic district rules are relaxed, opening up more replacement window markets, installers will have to abide by the EPA's Lead Renovation, Repair, and Painting (RRP) rules. Read more about RRP and lead-safe practices.