Moravian Preservation Master Plan.indb - Society for College and ...

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Moravian College • Preservation Master Plan typically infiltrate windows at the perimeter of the window sash and at lower window rails. Water problems are exacerbated in areas which do not shed water, such as improperly sloped window sills, at rough surfaces, or in pockets created by missing glazing putty. Window sills are often the first elements to exhibit deterioration. Condensation that forms on interior window surfaces can also cause deterioration. It is important to distinguish moisture penetration caused by condensation from that caused by water infiltration. Each requires different remediation techniques. Windows that have been protected from the elements by exterior storm sash are not immune from moisture-related problems. Poorly ventilated storm windows can actually accelerate damage to wood and metal windows. Condensation forms as the warm interior air meets the cool exterior storm window. If there is no ventilation, condensation is trapped against the sash, causing failure of finishes and, ultimately, wood rot or corrosion. Window operation is impaired by loose joints and misaligned sash. Maintenance level painting often covers hinges and other moving parts, eventually causing excessive paint build-up. This can lead to sticking or inoperable sash. Window Repair Historic windows should never be replaced unless they are missing or beyond repair. Contrary to popular belief, repaired historic windows will last far longer than most modern replacement windows because they are made with superior quality materials and craftsmanship, especially wood windows. Epoxy consolidants may be used to strengthen and save deteriorated wood elements, especially at sills. Special patching compounds may be used to repair steel window parts. Warped wood sash and bowed or bent steel sash can often be repaired by skilled craftsmen. Replacing deteriorated parts, not the entire window, is the preferred solution, using elements that are visually and physically compatible with original. Historic windows are easily disassembled for cleaning and repair. Unlike modern replacement windows, historic window units were constructed so that damaged portions could be repaired or replaced one part at a time. Individual window elements that should be retained include frames, sash, muntins, glazing, sills, lintels, hardware, heads, hoods, paneled or decorative jambs and moldings, interior and exterior shutters, and blinds. The damaged portion of a window component should be replaced with material matching the original material and fabrication techniques. Any repair should match historic window sash, muntin configuration, reveal depths, glass-toframe ratios, glazing patterns, frame dimensions, trim profiles, and decorative features. Replacement glazing should match the qualities of the historic; low-E and reflective glazing are not appropriate in historic contexts. New window elements should be based on surviving prototypes including hood molds, sash, sills and interior or exterior shutters. Windows should also operate smoothly. Window mechanisms such as sash locks, cords, and weights should be maintained, repaired and, if necessary, replaced. This approach results in cost savings, because when properly maintained, historic windows can last for decades. Removal of prominent window features should be avoided because it damages a building’s architectural integrity. Important features include frames, sash, muntins, glazing and glazing patterns, sills, hardware, heads, hoods, paneled or decorative jambs and moldings, interior and exterior shutters, and blinds. They should not be blocked, infilled, or obscured. Window Weatherization Historic repairable windows should never be replaced with new units simply as a weatherization measure. Most loss of thermal efficiency at a window occurs around a leaky frame rather than through the sash itself. This can be addressed through simple weatherization techniques such as installing weather-stripping or storm windows. Weatherization techniques can greatly increase the energy efficiency of the overall building envelope and are always less costly than wholesale replacement of an entire window unit. Weatherization Historic windows can be made as energy efficient as new windows through the installation of weatherstripping. Weatherstripping methods include installation of compressed metal or spring clips or compressed foam tape. Weather-stripping is installed between the window frame and operable sash and along the meeting rails of the sash. Do not apply reflective or insulating film to window John Milner Associates • October 2009 • Chapter 9 • Building Guidelines • 306
Moravian College • Preservation Master Plan glass. Blinds or insulating curtains may be added to the interior for privacy and increased thermal performance. In addition to weather-stripping, there are a variety of retrofit techniques that can provide thermal efficiency. These methods are less expensive than wholesale replacement and insure that the greatest amount of historic material is retained. Storm Windows Storm windows help achieve increased thermal efficiency without removing historic materials and features. Storm windows are appropriate as long as they fill the window opening completely, without the use of spacers or filler panels. Wood storms with removable storm sashes and screens are available commercially and are particularly appropriate for use on historic buildings. Stiles and meeting rails should align with those of the prime sash. Do not install exterior storm windows in a manner that damages historic windows frames. Exterior storms should either be painted or acquire a factory-applied finish matching that of the prime sash. Bronzed and silver mill-finish treatments are not appropriate. Low-E and reflective glazing are also not appropriate in historic contexts. Interior storm windows are also available and are already being used in a number of Moravian College buildings, particularly on the Priscilla Payne Hurd campus within the Central Bethlehem Historic District. Because interior storm windows maintain the appearance of the exterior facade, they are preferable, and often less expensive, in cases where the windows are non-operable. Inexpensive and reversible magnetic storms can be removed in warm weather so that windows can open. Permanent interior storms are more appropriate for institutional buildings. Install interior storm windows with air-tight gaskets, ventilating holes, and/or removable clips to avoid condensation damage to wood or steel sash. Where interior storms are used, sufficient ventilation must be provided at the historic prime sash to avoid moisture condensation that will damage the historic unit. Window Replacement and Alteration Total replacement of all windows on an historic building is not a preservation treatment. Peeling paint, broken glass, stuck sash, and air infiltration are problems that can be remedied; they are not valid reasons for replacement. Windows should only be replaced when they have reached the end of their service life and the majority of the window components have deteriorated beyond repair. New windows should match the originals in material, finish, configuration, setback, profiles, and all other visual and reflective qualities. Details such as sash, muntin configuration, reveal depths, glass-toframe ratios, glazing patterns, frame dimensions, trim profiles, and decorative features should be faithfully replicated. A number of window manufacturers make customized replicas of historic sash and frames. They also offer more generic reproduction historic window lines. Both are much more costly than proper maintenance and repair of existing historic windows over their life-cycle. Replacement windows should always be based on the original in all respects; installation of a generic historic window is not appropriate. Steel Windows The replacement of steel windows can be more costly than repair work. Even large scale replacement of custom parts can be more cost effective. When planning for steel window replacement, it is important to understand that many steel windows are often anchored into the surrounding masonry. Steel frames were typically built into the masonry structure during the original construction. Replacing steel frames may involve costly masonry disruption around the window opening. Removing steel frames by cutting off the anchors and leaving the anchors embedded in the masonry is not acceptable. This will leave embedded steel anchors in the surrounding window masonry, which can lead to major masonry disruption when these anchors corrode and expand. The cost of dismantling, rebuilding, and repairing the surrounding masonry should be factored into any cost analysis of steel window replacement. Modern steel windows are made of a mix of rolled and pressed steel, bronze and brass sections, and aluminum glazing beads, while the originals were manufactured with rolled steel sections. New steel windows rely heavily on weatherstripping to prevent water infiltration. Aluminum replacement windows are not acceptable alternates for historic steel windows. Steel windows are characterized by thin section details, a testament to the strength of steel. Aluminum is not strong enough to recreate John Milner Associates • October 2009 • Chapter 9 • Building Guidelines • 307
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Preservation Master Plan for Moravi
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