Denver University Johnson McFarlane Hall
Several Unique Challenges
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 was 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.
Construction 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 was a major consideration
Since
the perimeter of the roof consisted of over 85% gravel stop, safety
for both the roofing crew and the student and other university population
was a major consideration. Warming lines were established both 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 rood 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,
we 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.
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 allowed us to complete 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 overlaid 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 were set in a continuous later
of Carlise-SynTec Fast 100 adhesive. The flat areas created by the tapered
EPS were then overlaid with Carlise Fleeceback membrane set in FAST
100 adhesive, while the remaining sloped areas were covered with .060"
Carlise EPDM membrane, 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.
