In order to preserve the integrity of historic city neighborhoods, the Cambridge Historical Commission has the responsibility to oversee updates to architectural details on “places and buildings that are significant for their history or architecture.” This mandate most particularly applies to exterior details that are visible from a public way. This can present a balancing act when it becomes necessary to replace historic wood window sash with units, which must satisfy modern requirements for energy efficiency.
For an example, the Commission and their preservation consultant offered guidance for new windows, which were proposed for replacements for an historic Victorian we were renovating in the neighborhood of Brattle Street. All of the existing double hung windows were to be replaced with custom wood window sash that needed to be upgraded to meet modern energy standards. The issue was that the muntins of the original windows dividing the sash lights were thin and delicate. These had to be maintained, per the Commission, which was a challenge due to the thicker, high tech, insulated glass.
This our local millwork fabricator was able to achieve, with careful planning. The thicker glass is also significantly heavier than the original windows, so much so that they would not have worked with a modern spring-balance operating system. This meant that he had to create a traditional jamb with insulated weight pockets, so the new units could be operated with a traditional weight system.
We are grateful for the guidance provided by the Commission for this project, which included rake trim details at the dormers, the front doors, and some of the details of a conservatory. Their collaboration contributed to the success of this project, but most particularly as regards the upgrades to the traditional wood window sash.