The Pros and Cons of Restoring and Replacing Wood Windows  

Half a century ago, most architects were occupied with designing new buildings. Rarely did they debate the pros and cons of keeping any part of an existing structure, let alone the structure itself-unless the building had an established historical provenance. New construction cost less and was better, while restoring a building was often considered to be prohibitively expensive, and not worthwhile.

Times have changed. Today, more than 90 percent of construction already involves existing structures, many of which are historic, notes Kirk Cordell, executive director of the National Center for Preservation Technology and Training of the National Park Service. Restoring a city row house is now de rigueur, reinventing historic office buildings as condominiums is happening across the country, while industrial buildings and former churches are being adapted as offices, schools and housing.

Clearly, practitioners increasingly require the skills for restoration, adaptive reuse. Architectural graduates must also be prepared. "It's part of the basic toolkit they need to come in with as much as they need to learn CAD," says T. "Gunny" Harboe, AIA, vice president of the preservation group at Austin AECOM in Chicago.

Virginia State Capitol, 1785-92, awaiting restoration by Hillier Architecture. Architect: Thomas Jefferson Photo courtesy of HillierArchitecture

Evaluating Significance

Since windows are arguably the most dominant visual element of a building, decisions regarding their treatment are critical. While ornamental windows and windows in historic buildings are clearly worth special attention, windows on any existing building-be it boathouse, townhouse or lighthouse-need to be analyzed.

The first step is evaluating the significance of the windows and planning for their repair or replacement. This includes investigating historical significance, objective analysis of the windows themselves, and subjective considerations of the architectural brief-such as sustainability, historical integrity, adaptive reuse or saving taxpayer money.

Essential is an understanding of how windows are made and the sometimes arcane vocabulary of their components. For example, "stiles" are the vertical members of a sash, "meeting rails" are two horizontal members of the sash that come together, while "muntins" hold the window pane in the sash. Also essential is appreciating the basic functions of windows, such as admitting light, providing fresh air, providing a visual link to the outside, and enhancing the appearance of the building.

The Preservation Brief onThe Repair of Historic Wooden Windows published by the National Park Service, characterizes ‘significance' in the broadest terms. It states that windows should be considered significant to a building if they: are original, reflect the original design intent for the building, reflect period or regional styles or building practices, reflect changes to the building resulting from major periods or events, or are examples of exceptional craftsmanship or design.

"As ‘character defining features,' windows are subject to a rather strict analysis," says Dr. George C. Skarmeas, AIA, Principal, Director of Historic Preservation for Hillier Architecture. He lists the areas in which all projects, small or large, simple or complex, are evaluated:

• Significance as character defining features. Determine if windows are original, and what changes have been made over time.
• Presence of significant fabric, information and historic evidence. This includes paint structure and history of paint layers, i.e. a comprehensive seriation analysis.
• Performance characteristics, both as an element of the original design, and construction and as an element of a new use plan. This area, he notes, is one of the most difficult to deal with.
• Overall condition assessment and organization in different categories of conditions and deterioration, such as good, moderate, and severe.
• Treatment options, including surface treatment to reconstruction and replacement.
• Construction costs
• Sequence of implementation. This embraces in-situ repairs to careful removal, and off-site restoration.

The information gained from such careful analysis, Skarmeas explains, will supply critical answers to a number of issues such as:

• The role windows play in the overall design of the historic resource.
• The important information they provide as part of the history of the building-its original colors, sequence of colors, and finishes.
• Clues as to how they have performed over time and where their weaknesses are.
• Deterioration patterns that may exist.
• Performance limitations against modern criteria and expectations, especially if there is a significant change in use.

A graphic or photographic system will record existing conditions and illustrate the scope of any necessary repairs. Another effective tool is a window schedule, which lists all of the parts of each window unit and notes their condition.

In any analysis the following should be noted:

• Window location
• Condition of the paint
• Condition of the frame and sill
• Condition of the sash, rails, stiles, and muntins
• Glazing problems
• Hardware
• The overall condition of the window such as excellent, fair, poor

Equally important is documentation regarding the qualities inherent in the windows, which make restoration worthwhile and, on occasion, have been known to evoke inspiration.

Many factors, such as poor design, moisture, vandalism, insect attack, and lack of maintenance can contribute to wood window deterioration, but moisture is the primary contributing factor in wooden window decay. Sills seem to fail first because they are exposed to beating sun, freezing rain, snow and bird droppings.

Conforming to Standards

Colonial sills pitch at a modest four or five degrees and are therefore more likely to collect moisture-trapping soot and dirt. Today's sills are usually pitched at a steeper 11 degrees and higher. The bottom rail on the lower sash is also likely to be more impaired because of its exposure to weather. The most deteriorated windows on houses are most likely to be found on the top floors. In the eastern U.S., west-facing facades take the brunt of wind-driven winter storms and rapid temperature drops after afternoons of baking winter sun.

Even if a building has been conscientiously maintained window deterioration occurs. The Georgian Federal landmark Pennsylvania Hospital in Philadelphia-the first hospital in the country-has reached a point where, after 250 years, one more coat of paint will not suffice. Termite damage, dry rot, powder beetles, and all kinds of conditions are under the paint, reports Alvin Holm, AIA, who is fund raising chair for the preservation of the original Pennsylvania Hospital building.

Preserving the original dimensions of muntins is a problem when replacing single panes of glass with thicker insulated panes. The widths of muntins have evolved from nearly one-and-three-eighths-inch during the Colonial period, one-and-one-eighth-inch during the Georgian period, seven-eighths-inch during the Federal period, to as little as one-half-inch during the Italianate period. One-half-inch was too thin for practical purposes, and muntins were often broken and removed, so that larger panes of glass could be installed, reports craftsman Torben Jenk, who has restored many buildings in the Philadelphia area. He notes that an important shadow-casting feature is removed when the depths of muntins are reduced to accommodate the thickness of double-glazing.

The Secretary of the Interior's Standards for Rehabilitation (www.cr.nps.gov) defines rehabilitation as "the process of returning a property to a state of utility, through repair or alteration, which makes possible an efficient contemporary use while preserving those portions and features of the property which are significant to its historic, architectural, and cultural values."

The critical paragraph reads: "The guidance that is basic to the treatment of all historic buildings-identifying, retaining, and preserving the form and detailing of those architectural materials and features that are important in defining the historic character-is always listed first in the "Recommended" area." This is summarized by every restoration architect as giving first preference to retaining and repairing original materials wherever possible, or replacing in kind.

Parc Rittenhouse, Philadelphia, PA, before conversion by HillierArchitecture Photo courtesy of HillierArchitecture

These Standards are the historic preservation gold standard for national, state, local, and district authorities and preservation bodies. But buildings must confirm first to local landmark criteria, which, on occasion, are stricter in their interpretation. This can affect the project cost and construction phasing. An example is the conversion of the 1926, 17-story Philadelphia Parc Rittenhouse, formerly the Rittenhouse Regency into residential condominiums by Hillier Architecture. Under the Secretary of the Interior Standards, the preference is for all the original 1,000 wood double hung windows to be replaced with a compatible unit or restored. But since the building is registered with the City of Philadelphia Historical Commission, explains James B. Garrison, AIA, Associate Principal, Hillier Architecture, the Philadelphia Historical Commission prefers to see windows from the second to the fifth floors either be replaced in kind or rehabilitated. For upper story windows, they will consider compatible units of a different material that also meet the Secretary's Standards.

In the world of practice, questions regarding restoration or replacement are not always argued over the condition and functions of the windows themselves. "The biggest issue we have to confront is clients or contractors who say they must be replaced, or there is no other option," says Skarmeas. "But past experience has indicated that there is rarely a case in which windows are beyond repair and cannot be repaired, restored, and reused. While the costs may be high, there are technology, products, and methods today that allow us to restore deteriorated windows without resorting to a replacement program. The costs may be higher is some cases, especially if there is severe deterioration."

One common argument for replacement is the payback gained through energy conservation resulting from the improved U-values (BTU loss per hour) of modern windows. When the U. S. General Services Administration (GSA) Center for Historic Buildings, Office of the Chief Architect, analyzes different upgrade approaches, a number of quantifiable variables are included, which must be balanced against standards of stewardship and saving taxpayer money. As a rule, cost analysis favors replacement in kind of simple double-hung wood windows, such as those in the Department of the Interior Headquarters, says Rolando Rivas-Camp, FAIA, Director (see Sidebar: How GSA Approaches Restoring or Replacing Historic Windows). Skarmeas reports that he has rarely found a window replacement program that gives fairly substantial paybacks.

1 2 3 4 1. Main entrance, Navy Yard Building 101, Philadelphia, PA, before restoration 2.VITETTA Headquarters facing the parade ground, formerly Navy Yard Building 101, Philadelphia, PA, restored by VITETTA 3. Interior, Navy Yard Building 101, Philadelphia, PA before restoration 4. Restored interior, VITETTA Headquarters, formerly Navy Yard Building 101, Philadelphia, PA Photos courtesy of VITETTA

"We do not recommend replacing original wood windows for any historic building if the original windows can be saved," says Michael Holleman, AIA, Director, Historic Preservation, VITETTA. But when the firm restored the historic landmark former Philadelphia Navy Yard Building 101 and adapted it for office reuse and its headquarters, replacement was the only option. Constructed in 1910 in the Renaissance Revival style, the building housed administrative offices for the Marine Corps and was the barracks for enlisted men.

All of the original windows had been replaced with aluminum-framed windows in the 1950's. In poor condition and poorly crafted, with a mill finish instead of a paint finish like the original wood windows, and a configuration which did not correspond to the original division of the sash with muntins, the windows significantly changed the appearance of the building's facades, giving the structure a lifeless appearance. In addition, the windows were single glazed and thermally inefficient.

Also being a reinvestment tax credit project, the three-story VITETTA Headquarters needed to meet the Secretary of the Interior Standards. Given that the value of the tax credits were significant relative to the added cost of replicating the original windows and, as the existing windows needed to be replaced, the question became one of finding the right window system. After looking at a fixed versus operable sash, the firm decided on fixed windows because they were more economical, more energy efficient with lower operating costs, and required less future maintenance.

Getting the divided light and double hung look right was a major issue. The final choice was insulated glazing with adhered wood muntin bars and aluminum spacers behind the bars. The profiles of the sash and muntins were manufactured to match the original architect's drawings, as none of the historic windows remained.

Old Mackinac Point Light Station in Mackinaw City, MI restored by the SmithGroup Photographer: Gregory A. Jones, AIA

Preserving History and Delivering Sustainability

In some cases, historical value overrides today's requirements for thermal efficiency. An example is the Old Mackinac Point Light Station in Mackinaw City, Michigan. Having earned historic preservation status by guiding ships sailing though the Great Lakes via the busy Straits of Mackinac from 1892 until 1958, when it was replaced by beacons atop the Mackinac Bridge, the Tudor-Revival building required restoration as a historic exhibit. The SmithGroup produced an historic structure report and managed the restoration. The upper and lower sashes of the single-pane windows were removed and fitted with modern brass-spring weather stripping, reports Gregory A. Jones, AIA, the SmithGroup's project manager. Nylon pile weather-stripping was added to the window, meeting rails and sash tops and bottoms. Paint was stripped and deteriorated portions of the wood exterior consolidated with epoxy, sanded, and repainted. In some cases, upper and lower sashes were replicated. Future plans include fabricating wood storm windows to replace the originals.

Window before and after restoration by SmithGroup at Old Mackinac Point Light Station Photographer: Gregory A. Jones, AIA

For other restoration projects, sustainability is one of the primary goals, along with maintaining historical integrity. When the Sisters, Servants of the Immaculate Heart of Mary, an order of Sisters dedicated to eco-justice, hired Susan Maxman & Partners to prepare a master plan on how to best utilize their buildings and land in the future, they requested that all renovations and land uses adhere to the principles of sustainable design. The Sisters also wanted the renovation of their Motherhouse, a significant structure in southeast Michigan, to be a model of sustainable design by including improvement to the energy efficiency of the windows. After an extensive analysis, the choice was made to replace the majority of the sashes. (see Box: The Motherhouse: Examining Sustainable Options for Restoration or Replacement).

The Motherhouse in Monroe, MI before restoration by Susan Maxman & Partners Photo courtesy of Susan Maxman & Partners

The GSA Approach to Restoring or Replacing Historic Windows The U.S. General Services Administration (GSA) is responsible for an inventory that includes over 400 historic buildings constructed between the early nineteenth and mid-twentieth centuries. Most were built during the 1930's, a period of high quality public building construction. Many retain original wood or steel windows that are character defining architectural features. In keeping with the Secretary of the Interior's Standards for Rehabilitation, GSA seeks repair and maintenance approaches that preserve original materials and design, repairing, and upgrading windows for functionality, energy efficiency, and improved security, as appropriate. For large and complex historic building projects, GSA often undertakes detailed analysis of alternative upgrade approaches to weigh cost, lifecycle, energy efficiency, functionality, and preservation tradeoffs. This analysis guides GSA in balancing conflicting goals between setting a high standard for federal stewardship and reaching sound and cost effective decisions. Sometimes through this process, GSA architectural teams devise new solutions that achieve preservation goals at a savings to American taxpayers. As a rule, GSA cost analysis has favored repair with replacement of irreparably damaged windows where the historic windows are large, multi-paned, and fabricated in steel or bronze. On the other hand, project-specific cost analysis has generally favored replacement in kind at buildings containing simple wood windows, such as the one-over-one double-hung windows at the Department of Interior (DOI) Headquarters Building. For each project undertaken, GSA examines the arguments for repair or a combination of repair and in-kind replacement that offer the best value for GSA federal agency tenants, along with stewardship of the nation's public building legacy. The Potomac Annex (Old Naval Observatory Campus) and the Department of the Interior Headquarters Building are both in Washington D.C., are listed on the National Register of Historic Places, and require review by the State Historic Preservation Officer for the District of Columbia under Section 106, National Historic Preservation Act (NHPA). Alterations must conform to the Secretary of the Interior's Standards for Rehabilitation, which give first preference to retaining and repairing original materials wherever possible. Necessary replacements, such as irreparably damaged windows, must match originals, including configuration, profile, dimensions, and detailing of sash muntins, mullions, meeting rails, jambs, and sills. Potomac Annex (Old Naval Observatory Campus), Washington, D.C. Constructed between 1843 and 1910, the site is a campus of small buildings. Specified work (not yet executed, as of 2005) is limited to repair of wood sash, repair and replacement of sash weights and cords, and caulking to improve weather-tightness. Estimated costs of repairing 438 windows in Building 2 (based on 1995 prices) are $122,041 ($279 per window) Window retention advantages include: Lower lifecycle cost Preserving original materials, maintaining historic integrity, and original appearance. Potomac Annex (Old Naval Observatory Campus), Washington, D.C., Architect: James Melville Gillis Photo courtesy of HABS/Library of Congress

Department of the Interior Headquarters Building, Washington, D.C. Department of the Interior Headquarters Building, 1935, Washington, D.C., Architect: Waddy Wood Photo courtesy of HABS/Library of Congress Constructed in 1935, the DOI Headquarters is a National Register-listed building in Washington's monumental core, near the National Mall. The building had 1,488 original wood double-hung, single glazed windows. New interior storm windows were installed for energy conservation and security (for blast resistance). The phased project combines repair and replacement in kind to reduce costs. Advantages of combined repair and in-kind replacement: Lower initial and life cycle cost than repair alone. Preserved original materials on main (E Street) facade, thus maintaining historic integrity. Replacement windows are located on a secondary façade. Original one over one, wood sash construction allows authentic replication. For future phases, the choice of repair versus replacement is to be determined, based on costs at time of construction. Disadvantage: somewhat higher lifecycle, long term cost

The Pros of Replication

Whatever the history of a building, whether it is significant in its own right, on the National Register of Historic Places, on a state or city's landmark list, or in an historic district-New York City has 55 landmark districts-each building is its own special case regarding window replacement versus window restoration decisions. Following is a compilation of the pros and cons.

Window and door of Sheppard Hall, City College, NY, before and after replacement Photos courtesy of Artistic Doors and Windows

Replicated windows duplicate the design intention of the original building. Specifications can run the gamut from construction drawings showing elevations and plans of new and existing windows, to a note on the drawing of a facade stating "New wood European casement windows to match original building windows-type A." Experienced wood window replacement fabricators provide detailed shop drawings and are familiar with landmark and government standards.

The major benefit of replacement windows is that they are new, enhance thermal efficiency, and offer all the benefits of new design and the latest fabrication technology, including:

• Weather-stripping. Older windows have either minimal or no weather-stripping.
• Insulated glass enhances energy conservation. A single pane of glass has a U-value of 1.0. An insulated pane of the same size with a one quarter-inch air space has a U value of 0.5 that reduces heat loss by one half. Insulated glass also reduces noise transmission.
• Glazing options. Tinting can subtly affect the color of glass. Replication of the waviness and miniature bubbles of old glass is possible but expensive
• Open sash with minimal effort unlike old ones, which may be painted shut or difficult to open.
• Life cycle sustainability. High quality new windows are rated for 60-plus years.
• Lead paint removed along with the old windows.
• Ability to alter details to meet any client and architect requested design changes, provided the building is not required to conform to landmark standards.
• Replacement is usually less expensive than repair, unless the existing units are in very poor condition.
• Sash only may be replaced. As long as frames are in good condition and require little to no repairs, sash, weather-stripping, weights and chains, pulleys and stops can be specified. This will keep both the interior casing-wallboard and plaster-and the exterior casing-brick, mortar, and stucco-in check.
• Relatively easy to have a manufacturer replicate just one unit if that is what the project requires.
• Many soft and hardwood species are available so that replicated windows may be manufactured from the same wood species as the originals.
• Old windows can be removed and new replacements installed relatively quickly. This translates into less disruption for the occupants.

The Cons of Replication

Replicating existing windows may not always be the best solution for a project. The disadvantages are:

• Removal of existing windows can damage surrounding components, such as casing, wallboards, stucco, and plaster.
• Opening up a wall can sometimes lead to unknown issues. Cost can be prohibitive if the landmark body or historic commission imposes rigorous requirements as to the look, type, and action of replacement products.
• Cost can also be higher than restoration, depending upon the condition of the existing windows.
• Reviews of proposed replacement details by landmark and historic commission bodies can impact the project schedule. Typically, up to three months must be set aside for a review process.

The Pros of Restoration

• Original materials are preserved, as is the original design intent.
• Old growth wood from which old windows are made is very durable because it came from larger trees and has a tighter grain.
• Original glass can be retained which, if it is hand-blown or float glass, may be an important element in providing a period look worth keeping.
• Glazing options. A significant feature of the restored sashes from the Virginia Capitol Building restoration was the choice of low-iron glass, which avoided the greenish tint of ordinary glass.
• Less damage to the materials surrounding the wall cavity than if the existing window is removed.
• Can be just a minimal expense if the conditions of windows are not too deteriorated.
• A fresh coat of paint goes a long way to making old windows look good again.
• Many new products are available to restoration companies to aid in proper restorative techniques.

The Cons of Restoration

• Original windows usually contain layers of lead paint, which require specialized removal. Lead paint removal is very costly.
• Existing windows usually have single pane glass, which, if retained, offers occupants and owners no enhanced thermal benefits.
• Generally difficult to get a restoration contractor if the restoration project is a small one.
• Can be very expensive, depending on the condition of windows. Many wood components may need replacing and the sash rebuilding. This is usually done in a shop that means the window openings may be boarded up for quite some time.
• The time required to restore a window in place can be lengthy, which translates into more disruption to the occupants.
• Depending upon the extent of restoration, items such as weather-stripping, glazing putty, and hardware may be neglected and not replaced. This results in less thermal efficiency and more frequent repairs.

Restoring the Virginia State Capitol Windows Thomas Jefferson's classical temple-form capitol building, completed in 1788, and added to from 1904 to 1906, has a total of 104 windows. The largest window is approximately five feet wide and 14 feet tall. According to James W. Dossett, architectural conservator with Hillier Architecture, the initial survey indicated that despite peeling paint and ordinary wear and tear, the windows were in good condition and could be restored. The repair process involved several steps. Decayed sash join will get repaired with epoxy, Virginia State Capitol Photo courtesy of HillierArchitecture First, the sashes and all hardware were removed on site, tagged with the window number, and then shipped to a restoration shop in Kansas City. Once in the shop, the sashes were stamped with a permanent identification number and sorted. Those needing more substantial repairs were pulled aside. Then, the sashes were stripped to bare wood. The frames were racked slightly to allow glue to be injected into the mortise and tenon joints. Muntins were routed to receive the thicker laminated glass. Dutchman repairs, a term that applies to cutting out a small area of damaged or decayed material and inserting and gluing a new piece of the same material, were made to large areas of decayed or damaged wood. Epoxy repairs were made for small fills and consolidation of damaged wood. Sanding, priming, spackling, more sanding, and a second priming coat were applied. A finish coat of paint was applied to match the 1906 color, as determined by historic paint analyst Frank Welsh. Brass sash pulley on left has been partially cleaned, Virginia State Capitol Photo courtesy of HillierArchitecture All windows were fitted with new laminated low-iron glass, including two layers of one-eighth-inch glass with a clear polyvinyl butyral (PVB) interlayer. The use of insulated glass was rejected because its thickness would have required removing too much of the existing muntins. The laminated glass has better thermal properties than single glazing and is better at reducing sound transmission. Also, the clear plastic interlayer cuts ultraviolet (UV) transmission, which is very important for the maintenance of historic artwork and furnishings. Low iron glass was selected because ordinary glass has a greenish tint. The sashes were shipped back to the site and re-installed with all new bronze weather-stripping. The wood frames were stripped to bare wood, and repaired prior to repainting. The original wood sills were clad in copper. Probes indicated that the wood was in good condition, and the copper was repaired in place and painted. All hardware was re-used, cleaned and re-furbished. New sash weights were added to compensate for the additional weight of the laminated glass.

The Motherhouse: Examining Sustainable Options for Restoration or Replacement The majority of the windows at the Motherhouse, a religious residential facility in Monroe, Michigan, renovated by Susan Maxman & Partners, were wood double-hung windows with single glazed true divided lights that were very energy inefficient. In order to make an informed decision to either refurbish or replace the windows, a number of criteria were developed by which to evaluate the alternatives. Windows were restored, left, and replaced at the Motherhouse by Susan Maxman & Partners Photos courtesy of Susan Maxman & Partners Thermal performance of the windows was a given and a key element in the Sister's goal of sustainability. UV protection and glare were important considerations for the failing eyesight of many of the aging Sisters. The windows had to be easy for the Sisters to operate and clean. The look of the windows was one of the significant character defining elements of the building and was important to both the State Historic Preservation Office and the Sisters. Construction waste, manufacturing waste, and energy spent in transportation were part of the project's sustainable design goals. Other client concerns included budget, energy efficiency life, and expected life of windows selected over available alternatives. Life cycle costs, however, were not evaluated. Design criteria included the following: Thermal Performance: U-values in summer and winter Shading coefficient Air infiltration Visual Health: UV transmittance Glare reduction Function: Ease of operation Ease of cleaning Ease of installation Maintenance Aesthetics: Historical accuracy State Historic Preservation Office Acceptance Sight lines Sustainability: Waste material generated Manufacturing waste Green materials Cost: First costs including screens Window Life: Life of window in years Alternative Options Eight alternatives were developed and analyzed during the design phase. A ninth was suggested during the bid phase. A matrix was developed which compared the seven alternatives to the criteria: Keeping the existing single-glazed windows Refurbishing the existing with a double-glazed energy panel Refurbishing the existing with a low-E double-glazed energy panel Refurbishing the existing with double-glazed heat-mirror glass was not possible for the existing windows. New aluminum clad wood windows with double-glazed low-E glass New aluminum clad wood windows with double-glazed heat-mirror glass New aluminum windows with double-glazed low-E glass New aluminum windows with double-glazed heat-mirror glass Refurbishing the existing frames and replacing the sash with double-glazed low-E glass. Analysis and Solution In general, refurbishing the existing windows with new double-glazed low-E glass ranked higher in all categories. The project was bid with this alternative. The bids for this alternative came in higher than the estimate. One of the bidders, however, proposed the idea of using double glazed replacement sash with low-E glazing in the existing frames. The cost was closer to the estimated price for the alternative with the refurbished sash. This solution met the Sister's combined goals of sustainability and preservation and was accepted pending approval of a mockup. The existing windows in the cloisters were lowered and the sash replaced with new steel windows. What was once an inwardly focused residence has been transformed into a new home for the Sisters that is strongly connected to the outdoor environment. Karin Tetlow is principal of Restorative Partners and writes frequently about design and construction.