Water is actually a homes worst enemy. No jokes; water intrusions can quickly escalate to structural issues, moisture problems and more “nay nay’s”. In light of the millions of gallons of rain we’ve had lately, today’s mini blog is dedicated to flat roof water draining. “Getting water off a flat roof”.

Flat roofs have unique characteristics that make them desirable in many situations; garden spaces and living areas are wonderful examples. Not so ideal for our North American winters, but these roofs do very well in climates that don’t suffer from large quantities of rain and moisture. But with these benefits, come unique challenges: the most important being the drainage systems.

First thing that should be mentioned is that a flat roof should never be 100% flat; it should have a slight pitch to drain the water off naturally. Getting the water off the roof isn’t the issue; it’s controlling where it goes (to minimize the amount of water surrounding a home’s foundation). There are three types of drain systems commonly used on flat roofs; each of these systems has their own pros and cons.

Regular cleaning and unblocking of the drains, gutters and scuppers is regular maintenance, which is often neglected. Each of these systems can/will become clogged with debris if they’re unkempt.


Rain gutters are the most common drain system in use for all types of roofs.

  • Inexpensive – gutters are the easiest types of drain systems to get and install
  • Keeps water from pouring off of the roof in an uncontrollable manner
  • Protects doorways and window openings
  • Can keep water from pooling and building up near the building foundation

Although they do have their benefits, they also tend to be favored less due to several reasons:

  • High maintenance – gutters need continual cleaning and upkeep all year long
  • Gutter brackets can make them hard to clean – installing screens can reduce this problem
  • Gutters may become brittle and crack. The brackets may also give way due to water or wet leaf weight
  • Winter freezing – ice builds up causing a dam which leads to cracking

Internal Drains

Normally found on larger roofs with the drain being somewhere near the center. The pipes drain the water down through the building’s roof, leading water safely away from the foundation walls.

  • Unlike gutter systems, inner drains will not freeze up and crack or fail during the winter. The building and walls naturally protect the pipes from the elements.
  • Inner drains are customizable as an attractive feature of your flat roof. Increase your building’s curb appeal and beauty with custom fittings.
  • Strainers for inner drains are best when custom-made to fit your roof and your particular climate. They assist in keeping any debris from clogging the drain.

Inner drains do have some issues that need consideration before installation:

  • Inner drains are the costliest of the three drain systems to install.
  • Maintenance and repair on an inner drain system usually requires a professional technician. This leads to an even larger expense.
  • Vigilance is necessary regarding debris on the flat roof with inner drains. A small amount of debris can completely clog the system. This can become a domino effect as water will have nowhere to go, creating standing pools of water.
  • Be sure there are an adequate and appropriate number of drains for the size of your roof. Not enough drains will cause a problem with water building up.


Openings in the outer walls or curbs along the roofline. When installed correctly, scuppers allow water to run through the wall, through a metal box; this is you top choice for draining water from your flat roof efficiently.

  • Low cost
  • Easy to almost negligible maintenance required
  • No clogging issues if scupper is large or wide enough
  • No leaf or debris build up, everything washes or blows off the roof
  • Water shoots out away from the building instead of down the side
  • Can add architectural appeal to roof line with custom scuppers

The only real negative with scuppers occurs when they hook up to a downspout or gutter. Because of the clogging habits of both of these attachments, it is a better idea to leave them off of the system.