Case Study Hospital Roof Blow-off
Early Tuesday morning as Hurricane Sandy was moving off of Long Island, Roof Services received a call from a hospital on the south shore of Nassau County that one of their roofs had sustained a near total blow-off. We were able to visit the site soon after and found that approximately 75% of an existing roof assembly on a 4th floor wing had blown off. At one point it was still actually attached and hanging down the side of the building ending approximately 18” above the ground.
We immediately began mobilizing to perform temporary repairs and first thing Wednesday morning our crew was onsite to remove the hanging section of roofing and the risk posed by its falling uncontrolled we then temporarily sealed the remaining vapor barrier on the now exposed concrete deck in order to provide temporary waterproofing.
We brought in the necessary materials for the comprehensive replacement of the roof assembly as soon as possible and began the roof installation two (2) days later.
For the installation of the new roof we gave special focus to the perimeter attachment knowing that this is how the old roof failed and this is how most catastrophic roof blow-offs occur through failure of the edge.
We installed double nailer of 2” x 6” dimensional lumber which was mechanically attached into the underlying original tongue and groove deck along the perimeter of the roof with heavy duty deck screws to provide a solid and strong attachment. Then to complete the edge of the roof we installed an extruded aluminum compressionary gravel stop which is mechanically attached through the roof membrane into the underlying wood blocking with heavy duty screws. This combination of solidly attached wood blocking and heavy gauge extruded aluminum gravel stop provides the most protection to the exposed roof edge as possible from wind uplift. In our experience of roofing on Long Island we have never seen an edge fastened this way fail due to high winds.
When responding to a catastrophic roof failure as occurred at this hospital, it is important to mobilize immediately to secure the area and provide temporary watertight protection then follow-up with a properly designed roof assembly that will provide long term watertight performance and resistance to blow-off in the future.