Window treatments generally approvable under the Secretary of the Interior's Standards for Rehabilitation, in descending order of acceptability:
In priority of preservation treatment
Retain and repair all windows in place.
Repair or replace portions of window units. All details should replicate the original windows. Contemporary mechanisms may be used.
Energy conservation may require more substantial alterations than the first two alternatives allow.
Retrofit double glazing in existing sash, retaining all other details. Tinted or bronzed glazing is not acceptable.
Install new sash with double glazing in existing frame.
Retain and repair existing windows and install compatible interior storm units.
Retain and repair existing windows and install compatible exterior storm units made of the same material as the existing sash.
A comprehensive unit by unit survey may show that a large number of windows are beyond repair and need replacement.
Replace those windows that are not repairable with units that replicate the original in material and visual qualities including true divided lights. Snap in mountings are not acceptable.
Replace those windows that are not repairable with units made of substitute materials, but which replicate the originals in every other way.
Replace those windows that are not repairable with windows of like or alternate materials that are similar to the originals.
Alternatives 8 and 9 are only acceptable under special conditions, such as in tall buildings where the replacement units will not be easily visible from ground level.
