3.8 Alterations in Existing Buildings and Historic Structures
The general goal of alteration projects is to meet these facilities standards for new projects. Renovation designs must satisfy the immediate occupancy needs and anticipate additional future changes. As they are remodeled, building systems should become more flexible and adaptable to changing occupancy needs.
Alteration projects are defined at three basic scales: refurbishment of an area within a building, such as a floor or a suite; major renovation of an entire structure; and upgrade/ restoration of historic structures.
In the first instance, the aim should be to satisfy the program requirements within the parameters and constraints of the existing systems. The smaller the area in comparison to the overall building, the fewer changes to existing systems should be attempted. Components, equipment and construction should match the existing as much as possible to facilitate building maintenance.
In the second case, the opportunity exists to approximate the standards and flexibility of a new building, within the limits of the existing space and structural capacity.
Where a historic structure is to be altered, special documents will be provided by GSA to help guide the design of the alterations. The most important of these is the Building Preservation Plan (BPP) which identifies zones of architectural importance, specific character defining elements that should be preserved, and standards to be employed. Refer to pages 1-14 for The Secretary of the Interior’s Standards for Rehabilitation and Guidelines for Historic Preservation. For some buildings a Historic Structures Report is also available. Early and frequent coordination between the architect, State Historic Preservation Officer, Regional Historic Preservation Officer, preservation specialists, external review groups, and other appropriate GSA specialists is imperative to timely resolution of conflicts between renovation and preservation goals.
To the extent feasible, GSA seeks to achieve the rehabilitation of historic structures. Rehabilitation is defined as the act or process of making possible a compatible use for a property through repair, alterations, and additions while preserving those portions or features which convey its historical, cultural, or architectural values.
In general, alterations in historically significant spaces should be designed contextually to blend with original materials, finishes, and detailing, and to ensure a uniform and inviting first impression. When substantial repairs or alterations are undertaken in significant and highly visible locations, opportunities should be sought to restore original features that have been removed or insensitively altered, to reestablish the original design integrity of the space. Alterations affecting the configuration of significant spaces should be as transparent as possible, using glass and contemporary materials, as appropriate, to minimize the visibility of the alteration(s) while subtly distinguishing new construction from original construction.
The architectural, mechanical and electrical systems in historic buildings often differ greatly from today’s design and construction standards, and frequently many of these building systems need to be upgraded substantially or completely rebuilt or replaced. The end result should be a building whose architectural, mechanical and electrical systems support its modern use while retaining its historic and architectural character.
Understanding the exact requirements of the user is essential to effectively implement the program for remodel projects. Close interaction between designers and users, to communicate and incorporate program information during the concept design phase, will enable the designers to meet the users’ needs without incurring excessive construction cost. Practical solutions often develop in a dialogue with the users that would not have been relayed by an administrator.
Alteration design requires ingenuity and imagination. It is inherently unsuited to rigid sets of rules. Each case is unique. The paragraphs that follow should be viewed as guidelines and helpful hints to be used when appropriate and disregarded when not.
Evaluation of Existing Systems
Every alteration project includes an evaluation which describes the physical condition of building systems, identifies variances from present codes, and notes available capacity for structural, mechanical, electrical and communications systems.
Code Requirements for Alterations
For most major renovations an evaluation of code deficiencies is appropriate. See Chapter 1: General Requirements, Codes and Standards, Building Codes. Code deficiencies that related to life safety, particularly egress, should be remedied. Strict adherence to the letter of the code is often impossible. An equivalent method of protection will have to be developed to achieve an equal or greater level of safety. See Chapter 1, General Requirements for additional information. Architects will be expected to work closely with the GSA regional fire protection engineer who will have final authority on life safety code compliance issues. Alternative approaches outlined in state historic building codes, rehabilitation codes, and performance based codes to resolve conflicts between prescriptive code requirements and preservation goals should be explored.
New work in alterations generally should meet current codes, unless a special hazard is created by combining new and old systems. Such conflicts should be resolved with GSA.
See Chapter 7: Fire Protection Engineering, for additional information.
Placing Mechanical and Electrical Systems in Renovated and Rehabilitated Buildings
Finding space for air conditioning, power and communications cabling is one of the biggest design challenges in remodeling work. Existing systems are usually totally inadequate, shafts are too small and ceiling space is too shallow. See Chapter 5: Mechanical Engineering, Major Alterations in Existing Buildings and Historic Structures and Chapter 6: Electrical Engineering, Major Alterations in Existing Buildings and Historic Structures.
Vertical Distribution. Space for new shafts can sometimes be found in stairwells, if the stairs are larger than required by code. Any element incorporated must have the appropriate fire-resistive construction and not impose on the accessible pathway. If elevator systems need to be replaced, elevator shafts can become duct shafts or electrical closets. The building exterior also offers possibilities if new vertical elements can be integrated with the façade design.
Original elevator doors should be retained. Design for new hoistway and cab doors should be based upon original door detailing, matching original materials and adapting ornamentation as necessary to comply with code.
Original hardware should be maintained in place and upgraded to remain functional wherever possible. Lobby and corridor floor landing indicators should be scaled to avoid destruction of original ornamental finishes, such as borders in stonework designed to frame original indicators.
Horizontal Distribution. Fortunately, many older buildings have tall floor to floor heights, which give the architect two options: a raised access floor or a very deep ceiling space.
Raised Access Flooring is an attractive choice for buildings that are being completely remodeled. Raised flooring can be lower than the minimum of 200 mm (8 inches) indicated for new buildings if floor-to-floor height is insufficient. It offers the same systems quality and flexibility as a new building.
The other option is to create a deep ceiling space and zone it carefully for the most efficient fit of all engineering systems. See section Building Planning, Planning Module, Floor-to-Floor Heights and Vertical Building Zoning of this chapter for zoning of ceiling space. Ceilings should never be dropped below the level of the window head. In historic buildings, care should be taken not to allow the installation of dropped ceilings to damage character defining architectural details and, if possible, to maintain visual access to such details. Carefully designed exposed system installations are encouraged in workspace where exposing systems will a) enable original ornamental ceilings and finishes to remain exposed, b) maintain original high ceiling volume and daylight in new open space offices, or c) avoid disturbing hazardous materials such as asbestos. Exposed systems in historic spaces should be designed to minimize interference with historic details.
In narrow buildings, it may be possible to create a furred horizontal space adjacent to the exterior and core walls, which can be used as a raceway for utilities. Vertical furring on columns and walls for receptacles is another possibility and can be integrated as an architectural feature. If space is tight, all-water or water-and-air systems should be considered for air conditioning, instead of all air systems.
Utility distribution in historic buildings is the most difficult because ceilings and floors often have to be preserved or restored. In these cases, decentralized air conditioning units with little or no ductwork become feasible. Pre-wired systems furniture, which is available in wood, is also a very good solution.
Placement of Main Mechanical and Electrical
Equipment. If new equipment is to be placed on the roof, the structural capacity of the framing system must be investigated.
Elevators. For complete building renovations a transportation study should be done, as described earlier in this chapter. If elevators need to be replaced, service can often be improved significantly by selecting higher speed elevators to fit into the existing shafts. New shafts are expensive to build and should be avoided.
Space Planning Strategies
Office Space. It may be necessary to design a slightly larger space allocation - about 12 m2 (135 square feet) per person - for office layouts in older buildings. This compensates for less than ideal bay sizes and existing walls configurations. The planning standards described earlier in the section Space Planning, should be used as much as possible.
Pre-wired systems furniture may be an appropriate solution for distribution of power and communications wiring in renovated buildings. Open plans have been used successfully in historic buildings. Furniture systems must be selected with great care to minimize any adverse impact on the historic features of the building. Modular furniture system dimensional planning restrictions, best adapted to large open office areas, may have limited feasibility in older structures with short or irregular structural spans.
Food Service. In many older Federal buildings, dining areas are located below grade in cramped, poorly ventilated and poorly lit spaces.Major renovations are a good opportunity to correct this situation. Cost considerations may prohibit moving the kitchen, but light and air can be brought into dining areas by excavating and then glazing to provide views of sunken courtyards outside the dining room.
Office Space. Where existing office space is altered to an open plan, noise isolation of the ceiling system should be a minimum of NIC 20. Noise isolation class between rooms should be NIC 40 in Class B spaces and NIC 35 in Class C space. See the section Special Design Considerations, Acoustics, Design Criteria for Building Spaces of this chapter.
Historic Buildings. Hard surfaces often predominate in old buildings and create resonance and echoes.While it may be possible to upgrade the acoustical environment, this should not be done at the expense of the historically significant features of the building.
Alteration of Building Elements
Exterior Closure. See Chapter 4: Structural Engineering, Alterations in Existing Buildings. Most older buildings lack adequate insulation and vapor barriers, but these can be added from the inside at the time of alteration. Design alterations to avoid damaging original finishes in preservation zones (as defined in the BPP or HSR).
Refer to Building Elements Section of this chapter for references regarding treatment of existing windows.
Exterior masonry should be cleaned if necessary and repointed. Joints should be resealed.
Re-roofing. Where existing roofing is to be replaced, it should be completely removed and the substrate prepared for new roofing. The new roofing system should not be of greater weight than the old, unless a structural analysis shows that the framing system can carry the additional weight. Do not overlay new roofing membrane systems over existing roof membranes. Installing new roofing systems over an existing roof will place additional load on the building structural system and may trap moisture remaining in the original roof. This trapped moisture can facilitate the premature deterioration of the building materials.
Uncommon Products Used In Rehabilitations
In historic preservation it may be necessary to specify uncommon materials that may be hard to find. These products may be described with the supplier’s name and address in the specifications. If more than one supplier exists, multiple manufacturers must be stated. The specifications should also contain a note stating: “The use of a trade name in the specifications is to indicate a possible source of the product. The same type of product from other sources shall not be excluded provided it possesses like physical characteristics, color and texture.”
New equipment should not be installed on existing materials that are very difficult to adapt for proper connections. These may include: structural glass, marble, and ceramic tile.