Anything sitting on a low-slope roof — a curb, a wall, a wide penetration — blocks the water trying to flow past it, and without a cricket to divert that water around the obstruction, it ponds and eventually leaks.
On a low-slope roof, water has to flow across the surface to the drains, and anything in its path — a mechanical curb, a skylight, a wall, a wide penetration — acts as a dam. A cricket (or saddle) is a small sloped structure built on the upslope side of an obstruction that splits and diverts the water around it, keeping the roof draining. When crickets are missing, too small, or poorly built, water ponds behind the obstruction, and standing water on a roof accelerates membrane aging and finds its way through the nearest detail. It is a slope-and-detailing failure rather than a material one.
The failure is predictable at every rooftop obstruction. The sections below cover the four aspects that matter most — ponding behind curbs and walls, missing or undersized crickets, positive slope to the drains, and cricket construction and flashing — and how to keep water moving to the drains.
These challenges rarely stay in one silo: the same discipline runs through our guidance on guardrail post penetration failures, what we have learned from roof insulation fastener backout, and how we approach under-slab vapor barrier failures, and it all ladders up to ACE’s broader design peer review and value engineering.
Ponding behind curbs and walls is the direct symptom, because any obstruction on a low-slope roof blocks the water flowing toward it and lets that water pool on the upslope side, and standing water accelerates membrane deterioration and pressures every seam and detail it sits on. A cricket that splits and diverts the water around the obstruction prevents the pool from forming.
The upslope side of a wide curb or a wall running across the slope is the classic ponding location, since the obstruction spans the flow and there is no path around it.
Because ponding both ages the membrane and drives water through details under sustained head, eliminating it with a cricket is a durability measure as much as a drainage one.
Representative of the cricket and ponding failures ACE finds in roof investigation and peer-review work. Illustrative distribution, not a published statistic.
Missing or undersized crickets are the root cause, because crickets are frequently omitted at obstructions that need them, or built too small and too flat to actually move the water around, leaving the same ponding a cricket is meant to prevent. Crickets sized and sloped for the width of the obstruction and the flow are what do the job.
A cricket that is too shallow simply relocates a smaller pool rather than clearing it, so the size and slope of the cricket matter as much as its presence.
Because the need for a cricket depends on the width of the obstruction and its position relative to the slope, identifying every obstruction that requires one is part of the design rather than a field decision.
A curb, wall, or wide penetration with no cricket, or an undersized one, dams the water flowing across the roof and ponds it behind the obstruction.
Build crickets sized and sloped to divert water around every obstruction, within a roof designed for continuous positive slope to the drains.
Water flows around the obstructions and reaches the drains, the ponding stops, and the membrane and details last as intended.
Positive slope to the drains is the context crickets work within, because crickets divert water around obstructions but the roof as a whole still needs continuous positive slope so the diverted water actually reaches the drains rather than ponding elsewhere. Designing the roof with positive slope and crickets together is what keeps the whole surface draining.
Dead-flat roofs and low spots defeat even correctly built crickets, since the water they divert has nowhere to go, so slope and crickets are complementary parts of one drainage strategy.
Because water on a low-slope roof only moves where the slope takes it, the crickets and the overall slope have to be coordinated so every part of the roof drains to a drain.
Get the crickets, slope, and flashing reviewed so water diverts around obstructions to the drains.
Schedule a consultationCall (866) 389-8883Cricket construction and flashing determine whether the cricket lasts, because a cricket is an added sloped structure with its own valleys, transitions, and flashing at the obstruction it protects, and poor construction or flashing at those transitions makes the cricket itself a leak point. Sound framing or tapered insulation with properly flashed transitions is what makes a durable cricket.
The junction where the cricket meets the curb or wall is a critical flashing detail, since that transition is exactly where the diverted water is concentrated and directed.
The most valuable move overall is identifying every obstruction that needs a cricket and building each with real slope and sound flashing within a positively-sloped roof, because ponding behind obstructions is a predictable, preventable driver of low-slope roof failure.
In ACE’s field work, most roof cricket and saddle failures problems trace back to a few recurring locations — Missing crickets at obstructions, Undersized / too-flat crickets, and Inadequate overall slope — rather than the open field of the wall or roof. The cost of resolving them climbs by roughly an order of magnitude at each stage: a detail corrected during design costs a fraction of the same fix during construction, which is itself far cheaper than a repair once the facility is operating. That economics is why we push envelope decisions as early in the project as possible.
Identify every curb, wall, and wide penetration that needs a cricket, size and slope each, and design the roof for continuous positive slope to the drains.
Confirm crickets are built to the designed size and slope with sound flashing at the obstruction, and that the roof slopes positively to the drains.
Where water ponds behind obstructions, add or enlarge crickets and correct slope so the water diverts around them to the drains.
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