Flat commercial roofs require a functional drainage system to protect the interior of the building from water damage. Your commercial roof may incorporate one of several different types of drainage systems, some using more than one. So, how does a flat commercial roof drain?

Is my roof really flat?

While your roof may be considered a “flat” roof, it is not truly flat. A totally flat roof would never drain. It’s recommended that every roof has a slope to direct water to drains at its center or perimeter.

A properly designed flat commercial roof will move water quickly to its drainage system. Water that does not have a drainage pathway will accumulate, unnecessarily adding weight to your roof. If there is any breach in the roof membrane or flashings, this standing water will find its way into the building.

Gravity is your roof’s best friend when your drainage system is in good working order. But it can also be your worst enemy as water tries to find its way to the ground. Pooled water will find the most minor crack or hole in your roof membrane or flashing and work its way inside. Standing water also degrades the underlying structure of your roof over time. It’s a warning sign that your roof is not draining correctly.

Get to know your drains.

It’s essential to know where your drains are and inspect them between scheduled roof maintenance appointments. It doesn’t matter how new or well-designed your commercial roof is – if it has damaged or clogged drains, you need to take immediate action.

Flat commercial roofs have several different drain systems, and many use a combination of methods. Your Mint Roofing expert can show you where your drains are and what to watch for.

Interior Drains

Interior drains are like the drain in your shower. They are positioned at a low point on your commercial roof and collect water from all directions. They are often covered with a leaf guard, which is an inverted strainer that collects leaves and twigs.

Interior drains are perfect for Minnesota winters because they keep melting snow and pooled water away from the outside walls and foundation of the building. Because they drain through pipes inside the warm building, they are not susceptible to freezing or cracking.

Overflow drains are often installed to discharge pooled water if the main drain is clogged with debris.

Since interior drains are usually covered by interior ceilings, walls, or beams inside the building, they are the most expensive drains to repair.

Edge Drains and Scuppers

As the name suggests, edge drains collect water around the perimeter of your roof and discharge it through a drainpipe or downspout on the outside of the building. As with home gutters, their purpose is to direct the water flow to prevent seeping back into the foundation or pooling in public areas.

Scuppers are a type of edge drain that appear as a rectangular opening located around the perimeter of your roof. They move water quickly off the roof and down an external downspout. Because they have a large opening, they are less prone to clogging than other drain types.

Edge drains are a simple design and relatively inexpensive to repair. Still, since they are exposed to the elements, they are prone to freezing during the winter months.

Bottom line; Keep it clean!

The key to a trouble-free commercial roof is always proper maintenance. Get to know where your drains are and inspect them from time to time, especially after a major storm or in the Fall when trees are losing their leaves. If your drains are clogged and have water pooled up around them, try to clear the blockage immediately. If it still doesn’t drain, you’ll want to give us a call to get it fixed for you before water starts finding its way inside your building and does real damage.

How long has it been?

If it’s been more than 12 months since your last commercial roof inspection, you should call us to schedule a professional inspection today. Our experienced Mint Roofing commercial roof inspectors will give you a full report on the condition of your roof and make sure you’re ready for the winter months.

Phone:  952-473-8080  24-Hour Line: 952-473-8181  Email: info@mintroofing.com 


Is my commercial roof really flat?

While commonly referred to as “flat” roofs, they actually possess a slight slope to facilitate drainage. A completely flat roof would retain water, posing structural risks and potential leaks. Properly designed roofs direct water towards drainage systems at the center or periphery to prevent accumulation.

How does a flat commercial roof drain?

Gravity drives water toward designated drainage points on flat commercial roofs. These drainage systems, which may include interior drains, scuppers, or edge drains, efficiently channel water off the roof’s surface. Regular maintenance ensures optimal functionality and prevents water damage.

What are interior drains, and how do they work?

Interior drains are situated at low points on commercial roofs, akin to shower drains. They collect water from various directions and drain it through pipes inside the building, safeguarding it against freezing. Leaf guards prevent debris accumulation, but clogs necessitate immediate attention to prevent water infiltration.

What are edge drains and scuppers?

Edge drains and scuppers operate around the roof’s perimeter, directing water away from the building’s foundation. Edge drains discharge water through downspouts, akin to home gutters. Scuppers, with larger openings, swiftly remove water but may require periodic inspection to avoid clogging.

How crucial is regular maintenance for commercial roof drainage?

Regular maintenance is paramount for commercial roof longevity and performance. Familiarize yourself with drain locations, inspect them regularly, and promptly clear any blockages. If drainage issues persist, seek professional assistance to prevent water intrusion and structural damage. Additionally, scheduling professional inspections every 12 months ensures early detection of potential issues, especially before winter.