Roof drain requirements for a commercial building in Winchester, KY are set by the plumbing code, not by whatever the original architect happened to install decades ago — and a surprising number of older buildings around Clark County are still running on a primary-only system with no real backup. That gap rarely causes trouble in a normal rain. It shows up the day a drain clogs during a heavy storm and the water has nowhere else to go.
How many roof drains does a commercial roof need?
Plumbing code sizes primary drains to local rainfall rates, and every commercial roof also needs an independently sized secondary overflow drain or scupper system.
The plumbing code sizes primary roof drains to the 100-year, 1-hour rainfall rate for the area, calculated against the roof’s actual drainage area — an engineering calculation, not a rule of thumb. Separately, every roof needs a secondary path for water: either overflow drains matching the primary drains in size, or overflow scuppers sized to roughly three times the primary drain’s capacity, with a 4-inch minimum opening. The secondary system is sized as though the primary doesn’t exist, because the whole point is what happens when it fails.
Why do older Winchester buildings often fall short?
A lot of Clark County’s commercial stock — older retail strips, converted warehouses, small industrial buildings — was built or last re-roofed under an earlier code cycle, when secondary drainage requirements were lighter or not enforced the same way they are now. Roofs like that can run for years without incident, right up until a storm overwhelms a clogged or undersized primary system and a structure never designed to hold that much water gets an expensive lesson in ponding load. Our drainage and ponding guide covers what standing water does to a roof once it starts collecting.
What does adding drainage or an overflow scupper cost in Winchester?
Bringing an under-drained roof up to a safe standard is repair-scale work, not a re-roof. Cutting in a new scupper or drain — tear-off, flashing, and often a small tapered-insulation cricket to route water toward it — typically runs $1,500-$7,500+, labeled as typical and depending on how many penetrations are needed and what the existing membrane and insulation look like underneath. See our full cost guide for how that compares to other repair work.
Common questions
Do I need a permit to add a roof drain or scupper in Winchester?
In most cases yes — altering roof drainage is plumbing and structural work that typically requires a permit. See our permit guide for what triggers one on a commercial roof project.
What’s the minimum size for an overflow scupper?
Code sets a 4-inch minimum opening dimension for overflow scuppers, and sizes them to roughly three times the primary drain’s rated capacity so a single scupper can carry the load on its own.
How do I find out if my roof actually has secondary drainage?
A roof inspection with an as-built review will show it clearly — see our inspection and condition report service if you’re not sure what your roof currently has.
Operated by Central Roof Repair. Call or text (859) 310-1209 to have a technician confirm your roof’s actual drainage capacity before the next storm. Code background on secondary roof drainage is published by IIBEC.
Last updated: September 26, 2026