How is a large low-slope roof surveyed?
A large membrane is surveyed by area. The technician maps the ponding, the drains and the seams, and marks each blister and split on a plan of the roof. The plan becomes the record for the repair and for every inspection that follows.
The parapet and the curbs are checked at the same time. Those are where the membrane meets the walls and the hatches, and they are the commonest source of a leak into the top floor of a building in the valley.
What do the river-side outlets need?
Outlets on the rear walls of valley buildings carry a large volume of water after a storm. The discharge is checked for a clear fall away from the foundation, and for a splash block or a short pipe that stops the flow from undermining the soil beside the wall.
A blocked drain on a large roof is often the reason water rises across a membrane. Clearing and testing the drain is one of the first steps in the survey, and the result is recorded against the drain's number.
How is the crew's access planned in the valley?
Access to a valley roof is by a stair, a hatch or a service lift, and the route determines the materials the crew can carry. The technician notes the access, the load limit of the lift and the time the building allows for noisy work before the schedule is set.
Occupants and tenants are told the days when the roof is worked. Where a commercial tenant has deliveries or customers at certain hours, the crew works around those times.
Why do valley roofs need the drains tested together?
On a large valley roof several drains often share one pipe or one outlet, so a blockage at one drain can back water up to the next. The technician tests each drain in turn and records the flow, so the blockage is found in the right place and the repair is not spent on a drain that works.
The drain basins are checked for a fall toward the outlet and for a rim that stands above the membrane. A basin set too high holds a pool beside it, and the pool is the place where the membrane begins to fail first.
How is a valley building's parapet kept sound?
A parapet on a valley building is often finished in a cap that has been painted or sealed several times. The technician checks the cap for loose joints and the flashing beneath it for lift, since water that runs down the inside of the parapet reaches the top floor directly.
Where the parapet is high, the crew works from a platform or a lift rather than from the roof edge. The platform is fixed for the day and checked before the crew steps onto it, and the parapet edge is marked where the work is under way.
