Crickets Behind Curbs and Units
The upslope side of any curb or large rooftop unit blocks the flow of water, and without a cricket, a dam of standing water forms behind it. A cricket, the little pitched saddle set on the high side, divides that flow and turns it around the obstruction. It looks like a minor detail and it is easy to get wrong, because the slope has to be steep enough to work and tied into the surrounding membrane without a seam running along the low line.
We build crickets from tapered insulation cut to a drawn pattern, covered with the same membrane as the roof, and flashed up the curb with a formed corner patch at every turn. On older buildings, where equipment was added over the years with no thought to drainage, we can find several dams on a single roof. Correcting them together is cheaper than correcting them one leak at a time, and it works hand in hand with tapered insulation and cover board work when the roof is being rebuilt.
Scupper Boxes, Collector Heads and Downspouts
A scupper is an opening through a parapet or wall that lets water leave the roof, and the detail around it is where leaks begin. The opening needs a formed sheet metal liner, soldered or sealed at its corners, extending past the face of the wall and back under the membrane. The membrane needs to be flashed into it with a clean termination, and the invert, the floor of the opening, needs to sit at the level of the finished roof surface, not above it. Where the roof drains through a scupper into a collector head and downspout, the head must be large enough to take a heavy storm without overflowing back onto the roof.
On an older building with a scupper through its parapet, a failed box stains the wall below and, where that wall is masonry, washes out the mortar joints season after season. That matters most on stock like the 1920s and 1930s civic buildings around the Pasadena Civic Center, where an owner expects the facade to outlast several roofs. We rebuild the box by hand, reset the flashing, and check how the downspout discharges, because water that leaves the roof and soaks the wall is only half-solved. Where gutters and downspouts need attention, our edge metal and gutter work carries on from the scupper.
Foothill Rain and Overflow Capacity
Annual rainfall here runs near 20 inches, most of it in a winter season that peaks in February, and the San Gabriel Mountains wring roughly 6 inches more a year out of the storms here than downtown Los Angeles receives. A roof that works in a light storm may not cope with a heavy one, so capacity matters as much as condition. We count the drains, check the size of the lines where we can, and look for an overflow scupper or secondary drain, a backup path when parapets could trap water on the roof.
Overflow openings are often missing or blocked, and they are the last defense before the weight of trapped water reaches the structure. We set overflow scuppers a measured height above the primary drain, so they stay dry in normal rain and open when the main drain is overwhelmed. On a hospital such as Huntington Hospital, the San Gabriel Valley's only Level II trauma center, or a research campus such as Caltech, water held behind a parapet can interrupt work nobody wants stopped, so the overflow route is worth checking before the rainy season, as part of preventive roof maintenance visits.
Keeping the Low Points Clear
Most drains clog slowly, but one windy afternoon can fill a strainer that was clean that morning. Strainers should be lifted and cleaned before the winter rains and again after any heavy wind, and the sump and lines checked for blockage. On roofs with terraces, planters or roof gardens, such as Plaza Las Fuentes across from City Hall, drains also collect soil and roots, and they need more frequent attention.
We record the drain locations on a roof plan with the condition of each, the date it was cleared and any defect noted. That plan lets a property manager hand the task to a maintenance crew with confidence, and it lets us compare one season to the next. When a roof is old enough that its drains need replacing, we say so in the same file and plan the work with a commercial roof repair scope, which keeps the problem from returning as an emergency.
Commercial Roofing Questions
How can I tell if my roof has a drainage problem or just a dirty drain?
Walk it two days after a rain. Shallow, scattered pools that vanish quickly are normal, while deep ponds that remain, or a drain bowl with water standing in it, signal trouble. If the drain is clear and water still stays, the slope or the drain height is wrong, and cleaning will not help.
Is an overflow scupper required on my building?
On a low-slope roof with parapets that would trap water, the building code generally calls for a secondary means of drainage. The details depend on the building's age and the code in force when it was built or last reroofed. We check what is there and what is missing, and confirm the requirement with the city before we recommend work.
Can we just cut a new drain in where the water pools?
Cutting a drain into a roof is a structural and plumbing job, and the line has to go somewhere. A new drain needs a sump, a deck opening, a connection that holds water and flashing that seals into the membrane. In many cases a cricket or tapered insulation corrects the pond without any penetration at all.
Does ponding shorten the life of a membrane?
Some membranes tolerate standing water better than others, and manufacturers set limits that differ by product. Water left on a roof for days weakens seams and speeds aging in nearly any system. Correcting the slope is cheaper than learning where the limit is.
What does a scupper repair look like from the street?
A sound scupper has a tight liner, a tooled joint, and a downspout that carries water away from the wall. Stains or bulged sealant call for rebuilding the box, not another surface patch.
