Replacement of Water Treatment Plant Roof Built in 1911

Built in 1911, the Citico Treatment Plant Filter House No. 2 is a 177-foot by 50-foot building with brick load-bearing walls, steel roof trusses, wood roof purlins, and wood decking. After inspection, it was decided that wooden materials would need to be replaced. Structural analysis indicated that the steel trusses were adequate to support a new roof, even using the wind loading from the current building code.

In the final design, the steel trusses were left in place, the wood purlins were replaced with steel channels, and metal decking and a modified bituminous roof were added.

In addition, the brick parapet was removed; a gutter system was added to divert rainwater away from the roof; and lead and asbestos abatement was performed.

The project had several challenges:
• The filters in this building are a critical component in the water treatment process. Therefore construction had to be phased so that at least half of the building remained serviceable and the filters were protected at all times.
• The existing roof drained used interior roof drains, which presented a potential contamination problem.
• During demolition and construction, it was discovered that the original building was not constructed as the design drawings showed, and that there was more decay than anticipated.

• Field investigation
• Measurement and sketch of existing building
• Inspection of truss bearing conditions
• Load determination/force analysis
• Truss analysis (FE software)
• Design of roof members and decking, temporary covers, protection for areas not under construction, demolition of roof, framing, rain headers, and ladder; installation of framing, scuppers, guttering, roof, ventilation, ladder, light fixtures, drainage, etc.
• Design for asbestos and lead abatement
• Construction administration
• Resident project representation

The project was very successful, although the work included hazardous conditions, including removing the old wooden roof and asbestos roofing and repainting all riveted steel trusses over a large number of drinking water filters. CTI’s design, construction administration, and RPR services assisted TAW and the contractors in successfully replacing a very old roof with a new one while assuring that the TAW employees and drinking water were protected and the production of drinking water was not interrupted at any time during the project.