WestCon Tribune

OCTOBER REVIEW

RE-ROOFING THE MARIN COUNTY CIVIC CENTER

Presented by: Chris Nelson, Technical Roof Services

At our September Westcon dinner meeting, Chris Nelson gave an excellent presentation about the re-roofing of the Marin County Civic Center designed by Frank Lloyd Wright in 1957. Located in San Rafael off highway 101, the Civic Center is known for its striking blue roof. The structure which is on both federal and state historic registrars is comprised of two buildings: the administration wing with the dome , dedicated on October 13, 1962 and the hall of justice dedicated in 1969. The roof area that Technical Roof Services, Inc. consulted on is approximately 220,000 square feet - quite a large undertaking.

Technical Roof Services (TRS) was commissioned in February, 1998, by the County of Marin to provide roof consulting services regarding the existing fluid applied and elastomeric roof covering systems. The cost of the project was $1,350,000 and the work was done between the summer of 1999 and the summer of 2000 with a break for the winter in between.

The main portions of the roof on the Administration building and the Hall of Justice are a series of long curved areas, referred to as barrel roofs. The roof structure is cast-in-place, lightweight structural concrete, varying from 3 inches thick to approximately 8 inches thick. Approximately 3.6 miles (19,500 lineal feet) of "concrete ridge bar ornaments" run the length of the barrel roofs and the circumference of the dome.

The circular ornamentation was also installed to complement the multi-arch, exterior appearance.

The original blue coating was a thin, plastic vinyl-chloride (PVC) based elastomer and was reportedly in failure before the Hall of Justice was completed. The Administration Building roof was recoated when the Hall of Justice was roofed. Around 1983 to 1984, a third fluid applied urethane roof system was applied to both buildings but not to the dome. Excluding the original PVC system that prematurely failed, the average interval between roof system coating applications has been about 15 years and the current coating on the Administration Building and Hall of Justice is approximately 15 years old. In general, the existing roof covering system, depending on the building section, includes two and three separate fluid applied elastomeric coating applications.

The existing roof coverings, depending on the building section, included two and three separate fluid applied elastomeric coating applications plus many previous repairs. Temporary repair attempts had also been made previously at various locations on both wings and the dome. The various existing fluid applied, elastomeric roof coating systems had failed, and needed complete reroofing. The membranes exhibited fracturing, peeling, and delamination.

The majority of the leaks aligned with the interior corridors at the sides of the skylights over the atrium which goes down through three floors. The goals of the project were to have no change in the overall appearance, match the original blue color of the roof and maintain existing ornamentation and profiles.

During the reroof project delaminated areas were visually identified, cut out around the edges and removed, then patched over before the new system was applied.

Many locations on all roof sections exhibited fractures through the old coating systems – some completely to the concrete deck. All fracture locations were identified and patched over before the new system was applied.

Another common condition was water and mineral deposits exuding from the mortar bed beneath ornaments. During the reroof project, a significant amount of old membrane was removed around ornaments, due to old system failure. Areas were patched over before the new system was applied.

Preliminary recommendations were to remove all membrane to the concrete decks. Due to difficulty of removing rubberized coatings, potential damage to the concrete and cost factors for removal, a good portion of the existing roof covering was left in-place during the re-roof project. Experimentation with sandblasting did not remove much of the existing membrane but did do significant damage to the deck surface. After a series of power washing tests at different pressures were tried, it was found that a psi of 3500 was sufficient to remove a lichen growth and adequately prepare the surface for recoating.

The buildings had various coating layers in place. Recognizing that the old membrane was not going to be fully removed and that each old coating might produce different adhesion problems, a series of adhesion tests were performed. The adhesion tests needed to be performed at all system levels.

Silicone urethane and acrylic systems were considered and adhesion tests were performed with both urethane and acrylic coatings, with and without various primers. In the end, urethane systems were specified.

Three manufacturer’s agreed to follow-up with greatly appreciated assistance. The manufacturer’s followed-up with adhesion testing and also performed 3000 hour, ASTM G26 Weatherometer testing and QUV b testing on the proposed blue color coating. Adhesion tests were performed on approximately 125 samples. Samples had fabric embedded in the liquid and were allowed to cure. One-inch wide strips were cut in the samples and the fabric.

We then had a blue custom color mixed by hand by an "old timer" in a paint shop – his visual match was unbelievably close when tested to ASTM standards. It was this hand mixed sample that was given to the three manufacturer’s to match and then test.

When the results from the Weatherometer testing and QUV b testing were in, the urethane blue color appeared more stable and experienced less surface degradation characteristics than the acrylic. The County elected to specify the urethane system.

Many safety considerations were reviewed as prudent for this reroof project. Not just for ease and thoroughness of worker applications but also for consultant and Building Department observation.

Scaffolding the building was recommended with guardrails, toe-boards and safety netting on the guard rail system with a center scaffold installed for "bridging" the three large arches over roads that go under the building.

Much of this review was taken from the TRS Website. For an excellent visual representation of the re-roofing process and Chris’ presentation, visit the TRS Website at www.trsroof.com. The photographs and documentation are very thorough and informative.