Do not infill windows with brick or wood; do not alter size of window opening to install larger or smaller sash.
Guideline for Windows
Retain original window sash whenever possible. Preserve through an ongoing program of maintenance and repair.
If new sash must be installed, choose the style, size and material that will match the original. Many window companies offer custom-built windows that can accurately replicate original windows; some of these include double-glazing and other energy-efficient features.
Do not infill window openings and install smaller windows.
Do not enlarge window openings to install “picture” windows.