Window replacement costs in Boston

In Back Bay, your windows are partly the neighborhood's business. The Back Bay Architectural Commission's guidelines for the residential district say original windows stay whenever possible. If one is past repair, the new one copies it: same opening, configuration, dimensions, style and material. Curved, leaded and stained glass must be kept. Openings can't be shrunk or stretched to fit a stock size, and a new sash can't have more or fewer panes than the original.

The guidelines spell out what fails. Vinyl, aluminum, metal-clad and vinyl-clad replacement sash are out. So are snap-in grids, grids sealed between the panes, metal panning over the frame, and tinted or reflective glass. What they call right for most buildings there is a large-pane wooden double-hung sash, one-over-one or two-over-two, with muntins through the glass. The commission's reach includes walls you can't see from the street.

There's an easier fix for drafts. Interior storm windows are encouraged and aren't reviewed at all. Exterior storms can work if the frame is slim, matches the window frame color and lines up with the meeting rail. Clear or mill-finish aluminum doesn't qualify.

If you do apply to replace, take good pictures. The Boston Landmarks Commission says applications are often rejected for poor or missing photos, and it suggests labeling each window so the close-ups match up. It may also want letters from window restoration specialists saying the old windows can't be saved.