- Building & Code
- Technical Historical Preservation Guidance
- Preservation Guidance: Exteriors
- Cleaning, Demolition & New Construction
Cleaning, Demolition & New Construction
CleaningWhen planning to clean an historic building, the initial assessment should evaluate the historic material, the reason for cleaning and the cleaning method. Cleaning should be undertaken only where dirt or other material obscures significant architectural features or is causing or has the potential to cause damage to masonry materials. Cleaning should not remove the patina which is evidence of a structure's history and age, and should never be performed for the sole purpose of achieving a "new" appearance.
Cleaning methods should never exceed 150 to 200 psi., since higher pressures can damage historic masonry units and mortar. Abrasive methods such as sandblasting should never be used. They are extremely damaging to historic materials in that they accelerate the deterioration of historic masonry materials, and can greatly change a building's appearance. If masonry surfaces were painted historically, they should remain painted.
This coating could have a specific protective function or play a part in the historic design and appearance which should be maintained. If the covering is non-historic and deemed appropriate for removal, it should be removed as gently as possible. We generally recommend that test patches be made, beginning with the lowest recommended concentration and working upward to find the appropriate level.
DemolitionDemolition should be kept to an absolutely minimum in a preservation project and limited to secondary areas or areas of extreme deterioration. Any demolition should be carefully planned to minimize impacts on historic features, materials and floorplans.
New Exterior Construction & Related DemolitionNew exterior construction and related demolition at historic properties can be a serious preservation issue. Just as historic buildings vary, new construction should be individually tailored to the historic building and its site. Our office is always happy to provide assistance in new construction projects and has developed general guidelines.
The primary objective is to determine if the property can accept exterior change without impact to the historic design, materials and site. Some buildings cannot accept new exterior additions due to these considerations. A side or rear secondary elevation is usually the best location for additions, provided it is removed from primary, character-defining historic elevations. Any new addition should not impact or change the general perception of the building's historic design. As part of this, it should be designed in a manner that is compatible with the architectural character of the historic building, using materials that match the historic.
The real challenge, however, comes in ensuring that the new addition is compatible without being a carbon copy of the historic building. While it should be clear to the casual observer that the addition is new and not historic, the design and materials must respect and reflect the original building.