Although restoring older windows entails a lot of work, the end result can be worth the time and effort

— By Stephen Gottlieb

Although aging windows can have their drawbacks — their paint may be peeling; they may be loose or may stick; they may be drafty — it is often viable to retain the original windows and resolve any problems with careful repair. In the long run, it may actually be simpler, more attractive and more cost effective to restore rather than replace. Also, you will have the window that was designed for the building in the first place with the original divisions, shapes and materials.

In historic buildings, there is an even greater impetus to reuse the original windows because they are a key element in the appearance and history of the structure. For this reason, replacing them should be considered only if the building does not have noteworthy historic significance or the windows have major defects that would make their repair unworkable.

In repairing the windows of historic structures, all restoration must comply with the United States Secretary of the Interior’s “Standards for Rehabilitation and Guidelines for Rehabilitating Historic Buildings.”

In weighing your options, the first step should be a survey of the existing windows. A professional consultant should assess their condition and develop the data necessary to determine whether it is best to repair or replace them. A qualified architect or engineer (A/E) with window assessment and specification experience — specifically, experience with window replacement projects — will be needed. Ask each firm being considered to submit a list of recently completed window repair and replacement projects. If they list no repair projects, they may not be qualified to assess existing windows from that standpoint and are likely to merely recommend replacement.

The consultant must obtain or prepare exterior elevations of the building showing all the windows. That means looking at each window, or a representative number of windows, in detail and noting their condition. For a representative sample, 15 percent is usually adequate: If a building has 500 windows, for example, surveying 75 will reveal the general condition of all of them if the survey included a proportional percentage of each type of window. Even 50 windows would probably be representative of the condition of 500 windows.

The extent of deterioration is noted on a separate page for each window surveyed. A chart showing the different types and sizes of windows is compiled. Then a narrative is written to describe the overall conditions found and the implications for window replacement or repair. A comparison should be made of the features involved in repair versus replacement and budgets for both alternatives prepared.

The repair budget would typically be an estimated price based on the prior experience of the surveyor on jobs carried through construction and prices obtained by that surveyor from reputable window contractors and manufacturers. To develop a replacement budget, drawings of the windows are sent to window manufacturers while the survey is in progress to get prices for providing comparable replacement windows. This price would be a budget number at so many dollars per window. A more refined price would be determined later if it became a firm replacement project.

The decision to repair or replace the windows will depend on the recommendation of the professional survey, the comparison of repair versus replacement, the quality of replacement available and the longevity of the options. If the existing windows were well made, have lasted many years and are in fairly good condition, the decision may be to keep them. If they were poorly made and are in poor condition, the decision will probably be to replace them.

Identifying Windows by Type
Wood windows can be pierced with a knife and have a dull sound when tapped with a knuckle or tool. They are subject to rot and paint loss, loose fit, worn or no weather stripping, broken sash cords and malfunction. Each element should be noted separately in the report.

Steel extruded windows were typical of the late 19th and early 20th centuries. The Hope Corporation manufactured most of them. Their individual parts often have a zee shape and small panes of about 81/2 by 11 inches. Hope windows are usually center pivot, casement or hoppers.

Metal clad kalamein windows are wood covered by galvanized sheet metal. They are often found on side property lines and frequently have chicken wire mesh inside the glass.

Bronze monumental windows are most typically found on the first floor of large public commercial or government buildings.

Steel extrusions or sheet-metal-covered kalamein windows are both magnetic and ring sharply when struck with a metal tool. Metal covered wood windows clack when struck. Their configuration is typically double hung two-over-two (two separate glass areas over two other glass areas).

Metal windows are long lived but are subject to corrosion, warping and drafts. Typical aging of these windows involves corrosion of the metal, stiff operation, inability to close and multiple layers of paint. However, they are durable and can be easily repaired by companies that repair these windows exclusively. Likewise, bronze monumental windows that exhibit corrosion and loss of applied finish are almost always repairable by specialist companies.

Getting the Job Done Right
Once the decision is made to repair the original windows, the work should be performed by a professional contractor or company that specializes in window restoration. The foreman for the job should have 10 years’ experience on restoration projects of similar size and scope.

It’s useful for the facility executive to have a general understanding of a proper repair process. That knowledge will help the facility executive manage the process and prevent problems from occurring; it will also help to identify qualified firms.

A restoration program should be prepared, detailing materials, methods, equipment and sequence of operations to be used for each phase of the work. Alternate materials and methods are acceptable if evidence can be provided of their successful use on comparable projects and a testing program is carried out to demonstrate their effectiveness on the project at hand.

Before beginning the entire job, shop drawings based on the existing construction and conditions in the field should be submitted for A/E approval, as should a mockup of the work using the methods and materials that will be used for the remainder of the project. The approved mockups will constitute a standard for all subsequent work.

For wooden windows, the contractor first inspects the window finishes to determine the original color, surface and the occurrence of surface defects. Stripping, preservative treating, consolidation, repair, weather stripping, priming, and painting or varnishing are then carried out as necessary. Existing sound glass and hardware should be protected for continued use. Damaged wood components should be replaced with materials matching the original wood profiles, sizes, and species; missing, broken or cracked glass should be replaced with new glass that matches the original as closely as possible.

All new wood for exterior exposure or contact with dissimilar materials must be supplied already preservative treated. Counterweight assemblies to remain at double-hung windows should be repaired and cleaned. Samples of all materials — wood, fillers, chemicals and treatments, finishes, refurbished and reproduction hardware — as well as copies of all manufacturers’ printed materials and safety data sheets must be submitted for A/E approval.

Any deviation from designs or details of the existing woodwork must be indicated on shop drawings. All putty or glazing compounds should be replaced, as should sealant joints between windows and masonry openings. A minimum of six joints should be installed on the building as samples for inspection and should remain in place for the duration of the job.

Be aware that lead may be present in the original paint, or asbestos in the original glazing putty, so there should be provisions to follow the appropriate handling and abatement procedures dictated by local codes. The quality standards of the Architectural Woodwork Institute and the standards of the National Wood Window and Door Association should apply to the work.

Restored wood windows must match the performance of new wood windows of similar construction and possess the qualities of structural soundness, operation, visual appearance and weather- and air-tightness comparable to those at the time the windows were installed.

Restoring Metal Windows
For Hope-type metal windows, restoration begins with paint removal accomplished by using small pneumatic chisels operated off a small portable air compressor to avoid the use of messy chemicals. Next, the glass is removed and saved for later reinstallation. Bedding putty is then chiseled out from behind where the glass was removed. If there is any twist to the sash, it is taken out at this time. The metal frame is then lightly sanded and wiped with linseed oil to remove any rust powder and provide a binder for the new putty.

New black linseed oil putty is installed in the frame, and the glass is pushed into it. Linseed oil putty is used because when it hardens, it contributes to the structure of the window. The putty at the front is then reinstalled and trimmed to match the top of the muntins inside. This provides the same appearance inside and out.

The frame is then painted with an oil-based paint, usually gloss black — a traditional color for windows of this type. The putty takes several weeks to harden, after which it is painted gloss black as well, bringing the whole into visual, authentic harmony. Missing hardware should be replaced to match the original.

Operation of the window usually improves with paint removal. Any additional freeing-up is accomplished by applying Teflon spray dry lubricant. Removing the paint and eliminating the warp from the frame usually allows tight closing of the sash and eliminates any previous draft complaints.

Although restoring older windows clearly entails a lot of work, the end result can be well worth the time and effort: durable, attractive windows that can produce magic for the building.

Stephen Gottlieb is an associate partner with WASA, an architecture, engineering and preservation firm headquartered in New York City.

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