Restoration of the North Carolina State Capitol Building

Title: Restoration of the North Carolina State Capitol Building

Award Category: Building Enclosure

Project Address/Location

1 East Edenton Street

Raleigh, North Carolina 27601
United States

Submitted By: Jason Mobraten

Company Info

Raymond Engineering - Georgia, Inc.

316 W. Millbrook Road
Suite 201
Raleigh, North Carolina 27609
United States

9196073773

[email protected]

Project Description and Background: The North Carolina State Capitol Building was constructed in 1833-40 at the same Raleigh site as the previous State House, which was destroyed in a fire in 1830. The Greek Revival architectural style was designed by architects Ithiel Town, Alexander Jackson Davis, and David Paton. Originally the Capitol was home to the General Assembly, Supreme Court, and Governor’s offices until the Supreme Court moved out in 1888 and the General Assembly moved to the Legislative Building in 1963. The North Carolina State Capitol was listed on the National Parks Services National Register of Historic Places in 1970; the Capitol Area Historic District, which the Capitol Building is the core of, was listed in 1978. Raymond was first retained to perform a comprehensive assessment of the building envelope (masonry walls and copper roofs) and mechanical systems of the Capitol Building, and provide a report with our recommendations and priorities, to enable the development of the scope of work for the Capitol restoration. The assessment was determined to be required due to several factors including persistent water leaks at the roof areas due to expansion and contraction issues with the copper causing seams and joints to crack requiring constant maintenance with the application of liquid applied coatings as temporary fixes. The granite gneiss stone was starting to show signs of deteriorations, specifically at the first floor and entry portico locations; additionally, open stone joints were allowing moisture into the building causing deterioration of the interior plaster and paint. Due to this observed deterioration a comprehensive evaluation was required to ensure that the stone was restored before conditions become worse to avoid any large-scale removal and replacement of the historic stone.

Scope: Prior to design and finalizing the scope Raymond performed a hands-on assessment to allow for a better understanding of the failures of the roof assemblies and stone walls. Due to the historic significance of the North Carolina State Capitol Building, recommendations for design would comply with the Secretary of the Interior’s Standards for Rehabilitation and with the recommended methods and approaches included in the National Parks Service (NPS) Preservation Briefs. Roof: The roof assessment included several test cut locations to observe the copper assembly, installation methods, and determine the extent of any deterioration of the wood decking. The following was concluded: The north and south copper flat roofs and rolled eaves were past their serviceable life and were recommended to be replaced with a new copper roof system designed with expansion joints. Replacing these roofs also required the removal of the rooftop mechanical equipment with the recommendation to permanently move the mechanical equipment inside the attic spaces. In the location of the current rooftop equipment, a low-profile copper clad roof hatch was recommended to be installed to allow for future attic mechanical equipment removal and installation. The hip and gable steep slope roof areas were performing poorly, and the internal gutters were past their serviceable life with several attempts at temporary repairs using liquid waterproofing, it was recommended that the steep slope roof areas and internal gutters were replaced to provide a continuous and contiguous water tight copper roof assembly. The copper clad dome was also showing signs of deterioration and allowing moisture to deteriorate the wood decking, however, due to the steep slope most water was easily shed. The base flashing was past its serviceable life and had received a temporary coating over its joints to reduce water infiltration. It was recommended that the copper dome panels were replaced with the base flashing to allow for a continuous assembly. Stone Facade: The gneiss stone was performing well considering its age and it was an indication of the high-quality design and construction of the Capitol facade. However, it was recommended that masonry treatments occur soon to prevent further deterioration that will require more invasive repairs, stone loss, and interior water infiltration. The following repairs were recommended, and the locations were identified during a hands-on assessment. All repairs were to follow the National Parks Service Preservation Briefs: 1. Redress of stone to scale off lose pieces. 2. Substitute stone repair 3. Crack injections 4. Dutchman repairs 5. Stone cleaning. 6. Mortar removal and repointing.

Solution: Roof: The design-build nature of the project allowed the entire team to work together from the beginning of design. Using all team members, we were able to determine the reason for the existing roof failures, such as not allowing for expansion and contraction, especially at the gutters. We were also able to develop several mock-up iterations of critical locations to develop the best long term and historically accurate installation approaches. The following test and approaches were critical for the success of the new roof system: 1. Hygrothermal WUFI analysis of proposed roof systems. 2. Structural improvements to the attic spaces that would allow the rooftop mechanical systems to be permanently removed from the roof, reducing expansion and contraction concerns and penetrations of the flat roof. 3. Copper roof mock-ups to review for attachment, seaming, water tightness and general seam layout. 4. Historic document reviews, including books and photographs to allow for a historically accurate copper design. Stone Façade: Design phase test panels or mock-ups were performed of all stone repair treatments. This allowed the project specifications to include the appropriate preparation and material application techniques, appropriate material mixes and colors. Additionally, these mock-ups allowed for the stone masons to have a better understanding of the requirements before they started actual repair work. Due to the historical importance of the gneiss stone and possible irreversible improper repairs, all Restoration Workers and Supervisors that perform masonry treatments participate in an ASTM E2659-18 on site training prior to initiation of masonry repair work. Custom mortar matching laboratory tests were performed to ensure the proper installation of mortar, this test included analysis of: 1. Color and texture. 2. Aggregate analysis. 3. Binder to aggregate ratio. 4. Proposed replacement mix. 5. On site mock-up samples

Value: The project team included several IIBEC members that were involved during the assessment, design, and construction phases of the project. All of these IIBEC team members contributed heavily to the success of the project, including: David Willers, RBEC, RRC, REWC, RWC John Willers, RRC Jason Mobraten, RRC, REWC Adam Cook, RRC, RRO San Bawi, IIBEC Member Our team of consultants provided a comprehensive assessment of the building and developed a restoration scope of work and cost estimates that provide a long-term approach for restoration of the building. The information developed during the assessment phase allowed for an efficient transition into design. The design was historically accurate and complied with the Secretary of the Interior’s Standards for Rehabilitation.

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