The historic building at right was damaged when adequate steps were not taken to protect it from work on an adjacent site. Photo: The Miami Herald/Chuck Fadely.

PRESERVATION
Tech Notes

TEMPORARY PROTECTION
NUMBER 3

Protecting a Historic
Structure During
Adjacent Construction

Chad Randl

Introduction

    Valued for their ability to convey the past through existing materials and features, historic buildings must also survive in an ever-changing present. That change is often characterized by new building construction and demolition activities on neighboring sites. Whether it is the modest renovation of an existing building or the demolition of an existing structure and construction of a new high rise, physical damage to an adjacent historic building may occur. It is important for both the historic property owner and those responsible for the neighboring work to give careful consideration to the potential risks. Early planning offers the opportunity to identify these risks and to determine successful ways to avoid them.

Problem

    The forces that contribute to the deterioration of a historic building, from atmospheric pollutants to the footsteps of visitors, often take decades and even centuries to exact their toll. Demolition activities and new construction on neighboring sites, however, can cause immediate harm to the physical integrity of a historic structure. In the instant it takes an improperly planned excavation blast to crack the foundation of an adjacent historic structure, or for a steel beam to be dropped from a construction crane onto its roof, significant damage may occur. Additionally, adjacent construction work can expose the neighboring historic building to concentrations of dust, vibration and fire hazards that would normally be experienced only over the course of many years.

   These concerns are often overlooked when a project is undertaken on a site adjacent to historic resources. In some situations, the historic property manager may be unaware of the nature and extent of work at a neighboring site. In other cases, the new construction team is not familiar with the particularly fragile character of the neighboring historic structure or decides to repair any damage after the fact rather than avoiding it from the beginning.

Before new construction was undertaken to the left of this church, a subcontractor was hired to design a protective system for the tile roof and clerestory windows. Drawing: Alan Shalders, Universal Builders Supply, Inc.

Solution

    Effective planning and protective measures initiated before construction takes place can prevent most of the damage that may occur to adjacent historic buildings. Depending upon the nature of the adjacent project, protective measures may be limited to documenting and monitoring the historic structure or may encompass a broader plan that includes encasing windows, independent review of excavation procedures and a range of other precautions. Cooperation between all parties can help to ensure that construction activity continues without interruption and that the neighboring historic building is preserved unharmed.

   The information presented in this Tech Note can serve as a basis for discussions between the historic property manager and the developer of the adjacent site aimed at ensuring the protection of the historic building in a cost-effective manner. This guidance is also applicable where adjacent new construction is undertaken on the same site as the historic structure.

   Although adjacent construction work often poses a more immediate threat than the incremental impact of rain and pollution, the best defense for both situations is that buildings be in good condition. A well maintained structure with tight mortar joints, strong connections between interior and exterior walls, solid foundations and sound plaster is at less risk than a neglected structure.

   Providing adequate protection involves the following steps:

1. consultation between the historic building owner and development team to identify potential risks, negotiate changes and agree upon protective measures

2. documentation of the condition of the historic building prior to adjacent work

3. implementation of protective measures at both the construction site and the historic site; and

4. regular monitoring during construction to identify damage, to evaluate the efficacy of protective measures already in place, and to explore and implement additional corrective steps.

Consultation