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Helipad Headaches: The Importance of a Properly Installed Vapor Barrier
A few years ago, our firm undertook a large roof replacement project on several sections of one of Pensacola, Florida’s leading hospitals. During the course of our work, the hospital began experiencing leaks in an another area of the facility – an area that was not part of our original scope of work. The hospital’s engineer asked our firm to investigate the source of the leaks.
After eliminating the roof areas adjacent to the leak locations, we began to look at the rooftop helipad for the hospital’s Life-Flight operations. We performed visual inspections and took core samples of the concrete pad and underlying vapor barrier. The results of the core samples made it clear that the waterproofing system under the concrete landing pad surface was deteriorating and was the source of the leaks.
After providing a quote for replacement of the 3,840 square foot vapor barrier and helipad surface, the owner issued a change order to our contract to remove the existing pad, repair the waterproofing system underneath and replace the pad.
As you can imagine, this was a complex and expensive project that likely could have been avoided for many years if the helipad had been properly waterproofed when it was originally constructed. And making this undertaking even more challenging was the helipad’s proximity above operating rooms, waiting areas and patient rooms. To help minimize disruption to daily hospital operations, we adhered to a schedule of starting work no earlier than 9:00 a.m. each morning and concluding each day’s work by 5:00 p.m.
The scope of work included:
- Using a crane for the removal and replacement of concrete on a roof
The size of the crane needed for this project and it’s required placement on the grass in the courtyard five stories below our work area was especially sensitive; so, large 12” x 12” x 120” timbers were placed under the crane. In order to provide the safest possible operation, our crane operator employed a ground-traffic monitor/flag-man as well as a certified signal man on the roof adjacent to the helipad. The signal-man guided the crane operator as the boom of the crane negotiated around two large live oak trees nearby. Near-daily afternoon rains (it was a Florida summer) required the replacement of the courtyard grass on which the crane’s “timber pads” rested after the project was completed.
- Exposure of the faulty vapor barrier
The debris resulting from the demolition of the helipad surface was placed in large steel “skip pans” and lowered via crane to a dumpster. Removal of the helipad surface was completed in eleven days and exposed the vapor barrier that was installed approximately ten years prior. After blowing the concrete dust from the vapor barrier, it was clear that this barrier consisted of only of two plies of organic asphalt felt embedded in moppings of asphalt. This type of application was the wrong type of vapor barrier for such an important function – to protect the interior of a hospital from moisture infiltration.
- Removal of the existing vapor barrier
Since the existing vapor barrier was permanently adhered with asphalt to the surface of a 3” reinforced concrete sub-pad, we had to use demolition saws and other demolition equipment to remove the sub-pad/vapor barrier in sections. After each section was removed, we would clean and prime the area of concrete deck newly exposed from under the existing sub-pad and then install a self-adhering vapor barrier in order to maintain a water-tight condition while we continued to work. We continued with this method over several days until the entire 3,840 square foot existing sub-pad was removed and the pad’s footprint was cleaned, primed and covered with this self-adhering vapor barrier.
- Frame-up and pouring a new reinforced sub-pad
Once the demolition was completed, the installation of the new sub-pad began. This was accomplished by first lapping reinforced steel rods (rebar) to the engineered specifications and then hoisting concrete up to the roof by crane using a large steel bucket to allow the concrete to be poured over the rebar frame. Once the sub-pad was complete, a “curing period” was required to allow the excess moisture in the concrete to evaporate.
- Application of the proper vapor barrier on the sub-pad
Once core samples indicated the new sub-pad was cured, it was ready be primed and the self-adhering vapor barrier properly applied to ensure it would perform effectively for many years to come.
- Frame-up and pouring the new concrete helipad surface
Following the proper installation of the vapor barrier on the sub-pad, the application of the helipad surface took place providing a 2:12 inch slope to an existing drain at the center of the pad. Following completion and adequate curing of the helipad surface, new reflective paint and tape was applied to guide the helicopter pilots when landing. The owner installed new landing lights after Standard’s scope of work on the pad was complete.
This substantial rooftop demolition and concrete installation project was completed in a safe and timely manner, with limited disruption to the hospital’s vital operations and no injuries.