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Before you replace your windows,
consider the following...
 

If you are thinking about replacing the old window sash in your house, you should know what your options are. Replacement window sash come in a bewildering variety of types and materials, many of which are inappropriate for the architectural style or age of Cambridge’s older houses. The Cambridge Historical Commission wants you to know your options before you make a decision to remove your old windows.

Table of Contents:
- Repairs vs. Replacement
- Storm windows
- Replacement windows options: single glazed; double glazed; wood clad; vinyl
- Broken windows
- More information
- Anatomy of a Window diagram

What is the “right” thing to do for historic windows?
You may not think your windows are particularly “historic”, but if you have wood windows in your house, you may want to think about what they add to the character and design of your property before replacing them with new windows.

In most houses, wood windows play a major role in defining the property’s “look” and creating an appealing architectural design. The Historical Commission always urges property owners to consider saving and fixing up old windows before replacing them.

Old wood window sash can be removed from the window openings, paint and putty buildup can be stripped, missing and damaged parts replaced or repaired, and the sash reinstalled in good working order. Repairing existing sash is always the Commission’s first choice of window treatment.

Why? Because the Historical Commission is guided by a standard of what is most appropriate to the age and style of a house, even for the plainest of old houses.

Old wood windows are valuable components of a house’s architectural style and keeping them conserves historic character, but beyond that, old windows are generally more durable than today’s replacement windows. One reason: they were milled from heartwoods that are more dense than the woods now used.

While repair is labor-intensive, an historic wood window can be repaired by a contractor for about the same cost as a lower-quality replacement window. Finally, with a good quality storm window, a wood window in proper repair is nearly as efficiently insulated as a double-glazed insulated replacement window. Contact the Historical Commission for more information about getting historic wood windows repaired.

FYI: If your house is located in a historic or neighborhood conservation district, or is designated a historic landmark, you need to contact the Historical Commission about applying to replace the sash before you sign a contract for replacement sash! In most cases, a public hearing will be scheduled to review your application.

"My house has storm windows; if I put in new sash, I can get rid of them!"
Combination storm windows provide insulation, protect the underlying windows, and house screens and storms in one permanently-installed unit, but old aluminum storm windows can be ugly and unwieldy. Nevertheless, there are attractive, effective, and easy-to-use storm windows on the market. The Historical Commission routinely approves storm windows without a public hearing, even for houses in historic districts, provided the shape and color of the storm matches the primary window.

It is worthwhile to pay a little more for a top-of-the-line storm window because it will be better insulated, more sturdily-constructed, and easier to operate. Top-quality storm windows are also available in a range of colors, including off-white and black, both of which are more appropriate for old houses than the standard bright white.

"The windows in my house are a mess; they just have to be replaced."
The range of replacement windows is huge but the quality also varies widely from very good to distinctly substandard. Because the market for replacement sash is so strong, innovations continually increase the options available to homeowners.

In general, replacement windows that match the materials, size, and pattern of the original windows are always preferable to vinyl, vinyl-clad, or aluminum-clad windows.

The homeowner confronts a number of decisions when windows are to be replaced:
    1. Should you replace with single- or double-glazed window sash?
      Single-glazed windows
      Single-glazed wood replacement windows are still available as a stock item and come in sizes that have been standard in Boston since the 18th century. One local manufacturer calls these their “Boston Pattern” windows.

      With an energy panel (an extra, removable, sheet of glass that is attached directly against the exterior of the window), a single-glazed window’s energy efficiency is virtually the same as a double-glazed window. A single-glazed window with a good quality storm window is also highly energy-efficient.

      Single-glazed replacement sash are the least expensive wood replacement alternative. In design, these sash come in all but the most elaborate of the standard 19th-century window configurations: these include 2-over-2, 2-over-1, 6-over-6, 6-over-2, and other combinations of double-hung window, all of which are found in traditional residential design (see Figure 1). In addition, the muntins (or dividing bars) on a single-glazed window can be narrow because they only need to support one layer of glass; this means the window looks more like a 19th-century window.

      The cost of a new single-glazed wood sash with a good quality storm window is equivalent to a mid-range double-glazed replacement window. Single-glazed sash are typically also easier to repair, since any damaged components can be patched or replaced without affecting the sash as a whole.

      Double-glazed windows
      Double-glazed, or insulated, windows are the modern standard for window technology. At its most basic, a double-glazed window contains two layers of glass sandwiched together for greater energy efficiency. Special glass treatments or gases added between the layers may enhance the window’s energy efficiency even further but can create strange optical effects, making the glass appear warped.

      Because a double-glazed window is heavier, it can be difficult to make the window look like a historic window, especially if the window has many small panes of glass. If the muntins are an integral part of the window frame, that is, if the glass panes are individually set into the frame, the muntins must be fairly thick to support the weight of two layers of glass. Sash of this type is called “true-divided light” sash.

      Recently, advances in adhesive technology have allowed the development of what are called “simulated-divided light” sash. In this type, two large pieces of glass are set into the window frame and grids of the desired pattern are permanently glued onto the interior and exterior surfaces of the window to simulate the look of a divided-light sash. Because the grids do not support the weight of the extra layer of glass, the simulated-divided light can more closely approximate the narrow-muntin look of an historic window. Often this window type is acceptable and gives a better historic appearance.

      Good quality, double-glazed windows, in both true-divided light and simulated-divided light configurations, are available from many manufacturers. They are generally more expensive than single-glazed windows with an energy panel or storm window.

      Keep in mind that double-glazed replacement windows are made in sizes based on national standards and these may not precisely replicate the dimensions of historic “Boston Pattern” windows; installation may thus require changing the size of the window’s “rough opening”, which is the actual hole in the wall made for the window. Also, different sash patterns (2-over-2, 2-over-1, 6-over-1) may only be available on a custom basis.

      Keep in mind, too, that double-glazed windows are a “closed” system: to maximize energy efficiency, each sash is manufactured as a single complex unit and the failure of any single component of that system can signal the failure of the unit as a whole. The sealants that close the double glazing have been particularly prone to failure, meaning double-glazed windows have a more limited life, sometimes only 15 years.

      Among the options available on replacement windows are a variety of systems for creating the appearance of the traditional grid-pattern of a wood window.

      Many low-end windows use a “snap-in” grid that attaches to the inside of the window. These can be detached from the window and lost, they are easily broken when people try to open the window by lifting on the grid rather than the window frame, and they cannot be discerned from the outside, giving the window opening a blank, highly reflective surface appearance.

      In other windows, the grid system is sandwiched between the two layers of insulating glass. Neither system looks right in a traditional, 19th-century house; they are never acceptable for replacement sash. A much better appearance is achieved with windows that have a permanently affixed grid on the exterior of the window or that are constructed with “true-divided lights.”

      A full screen over the window can also obscure the appearance of the window. In general, half screens that cover only the lower portion of the window are preferred.
    2. Should the window have a wood or a “clad” exterior?
      Some replacement windows are constructed of wood that is then “clad”, at least on the exterior, in a “maintenance-free” material, such as vinyl or aluminum. While the interior, wood, surface of the window can be painted or stained to match interior color schemes, the clad exterior cannot, or should not, be painted.

      Exterior cladding colors are determined by the manufacturer and choices may be limited. This can restrict the owner’s options on house paint colors. Wood windows do require periodic painting, but can be painted to complement changing exterior house colors.
    3. What about vinyl windows?
      Non-wood replacement windows almost always differ in their proportions and dimensions from traditional wood windows and this can distort the appearance of the house. The glazed surface area of the window can also be reduced in a non-wood window. Vinyl windows are unacceptable in historic and neighborhood conservation districts, or for landmark properties.

      In addition, vinyl windows are generally available only in lighter colors that are inappropriate for 19th-century houses, which traditionally had dark (black or very dark green) window sash. Vinyl windows are not made in the dark colors of traditional windows because the material could be deformed by excessive heat, such as that generated by exposure to sunlight. Other elements of vinyl windows, such as foam insulation materials, can also be degraded by the sun’s heat.
    4. What if the window breaks?
      It is generally difficult to repair an insulated replacement window. Peter Hotton, the Boston Globe’s handyman, has published details on how to make minor repairs to some aspects of a broken window (such as drilling a tiny hole in the outer sash to ventilate trapped condensation if the glazing sealant fails) but normally the way to “fix” a broken insulated sash is to replace it.

Where can I find out more about windows?

Figure 1. Anatomy of a Window
Credit: The Window and Door Manufacturers Association, www.nwwda.org/images/glossary/window_glossary.gif


Information compiled by the
Cambridge Historical Commission
831 Massachusetts Avenue, Cambridge MA 02139
phone: 617-349-4683
fax: 617-349-3116
TTY: 617-349-6112
http://www.ci.cambridge.ma.us/~Historic

October 2002

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