Blog
Vertical and scupper drains form a complete flat roof drainage system. These drains let ponding water on a flat roof drain off before it causes damage. The correct type of vertical drain depends on the flat roofing membrane, the type of drain insert, and whether the deck accommodates a lot of foot traffic.
(NOTE: Scupper drains are part of any appropriate drainage system for flat roofs, but they’re outside this article’s scope. Scupper drains direct water runoff laterally, through a parapet wall or curb, rather than downward like vertical drains. Read our article about scupper drains here).
Vertical Drains for Flat Roofs
Vertical drains (sometimes called interior drains) have three recognizable features:
- Its flange facilitates sealing and fixing onto the flat roof surface.
- It connects to the DWV (drain-waste-vent) system below the deck.
- It has a strainer, preferably made of die-cast metal. The strainer prevents debris, leaves, and wildlife from clogging the drain and causing standing water to pool.
As our main article mentions, scupper drains funnel water off flat roofs to prevent immediate or long-term damage due to ponding water.
This article will further discuss box scuppers’ uses, installation, and maintenance.
What Are Box Scuppers?
Box scuppers are closed or open metal boxes that drain water through the curbs or parapets on the roof’s edge. They can complement a flat roof’s internal drainage system to ensure efficiency or, in some cases, be its primary drainage system.
Parapets are low walls around a flat roof. Their main purpose is to prevent people from falling off. They also help contain gravel within the roof’s area. Read More
Photo source: www.reddit.com/r/CrappyDesign
The primary drainage system of a flat roof can fail due to debris clogging it or because it can’t withstand an intense downpour. Whatever the reason, water will pool, which can collapse your roof. Because of this, secondary (emergency overflow) scuppers are required by the IPC (International Plumbing Code) and IBC (International Building Code) for roofs with parapets.
The main function of overflow or secondary scuppers is to back up the primary one by draining rainfall water to prevent it from overloading your roof. Read More
Photo source: www.wncroofing.com
Engineers design roof drainage systems based on rainfall statistics. The ASCE (American Society of Civil Engineers) and IPC (International Plumbing Code) consider a 100-year rainfall (a rare and intense rainfall event with a 1% probability of occurring in any given year) measured during 15 to 60 minutes.
However, historical data has taught that drainage systems of most membrane roof systems will experience a downpour exceeding the 100-year design rainfall.
