The University of Denver Johnson-MacFarlane Hall presented several unique challenges.
The roof structure of the building consists of a concrete folded plate deck, with twenty-two valleys, each approximately 100′ long and 12′ from ridge to ridge. Along the bottom of the valleys, metal decking had been installed prior to the installation of a modified bitumen membrane over perlite insulation. Over the years, a considerable quantity of standing water had accumulated under the decking, and the metal decking was badly rusted. All of the metal decking and roofing needed to be removed to the concrete deck. All of this work had to be performed while the students occupied these dormitories.
Biggest Obstacle – Lack of Access
The biggest obstacle to overcome was the lack of access. The only set up area was located on the south end of the building, which was parallel to the valleys. A platform system needed to be designed that would allow removal of the existing debris and the stocking of the new materials, but would be removable to allow for the installation of the new roofing. Constructing non-penetrating individual modules from wood framing, and installing a continuous 8′ wide OSB deck from the north end to the south, approximately 260′ long, accomplished this. As the demolition of each section was completed, the modules were removed.
Safety – A Major Consideration
Since the perimeter of the roof consisted of over 85% gravel stop, safety for the roofing crew, the students, and other university population was a major consideration. Warning lines were established on the roof and on the ground below the areas of daily construction. A non-working, full time monitor was employed on the roof whenever any roofers were working outside the warning lines, and a man was dispatched to the ground during the tear off phases near the edge of the roof to caution the university population below.
The standing water remaining in the bottom of the concrete valleys posed a significant challenge. In the first couple of valleys, crews attempted to pump the water daily, cutting a hole in the next valley and inserting sump pumps. This proved to be too time consuming, because the concrete deck had to be dry prior to the application of the roofing, which often took several hours after the initial tear off operations. To solve this, a second crew was brought on to the project to tear off the next valley the day prior to the roofing operation and make the exposed valley temporarily watertight after allowing it to dry for most of the day. The cost of the temporary roofing materials was easily offset by the increase in production, and the second crew’s work enabled completion of the project in 60 days, rather than the 90 days in the original schedule.
Creating Positive Drainage
Creating positive drainage was accomplished by the design of Scott Reichert of Sr+Dk Consultants, Inc., and Jeff Sykes of Advanced Foam Plastics. Large V-shaped blocks of expanded polystyrene (EPS) were fabricated to infill the valleys from each sloped side to the next. A tapered EPS system was then laid over these blocks to slope to either side of the valleys, and flat stock EPS was installed up the remaining slopes to the ridges. The EPS and a cover board of Georgia-Pacific DensDeck Prime was set in a continuous layer of Carlisle-SynTec Fast 100 adhesive. The flat areas created by the tapered EPS were then overlaid with Carlisle Fleeceback membrane set in Fast 100 adhesive, while the remaining sloped areas were covered with 60 mil Carlisle EPDM membrane and fully adhered with bonding adhesive. New aluminum drip edge and spitters to match the existing building and the other two wings of the complex were fabricated and installed by D&D Monarch Sheet Metal, as were the rest of the sheet metal details.
Completed Ahead Of Schedule With Minimal Inconvenience
The project was completed ahead of schedule with minimal inconvenience to the students and personnel of the university.