DRAINAGE SOLUTIONS FOR FLAT ROOFS

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Why Is Draining So Important?

Flat roofs are prone to ponding, and standing water on a roof is never a good thing.  Standing water on a flat roof is especially worrisome, as it can cause the membrane to fail.  Ponding water also carries dirt and debris, and will leave dark spots, especially on white membranes.  This leaves the membrane vulnerable to UV rays, which can break it down and eventually cause it to fail – so drainage systems on flat roofs are extremely important. 

Even when there has been no rain for a while, you can still determine whether a roof has a ponding problem.  Look for dirty circles on the surface of the roof, or areas with algae or other vegetation are indications that water ponds on your flat roof.

The Causes of Ponding

There are several reasons that a roof might pond, including:

  • poor design (insufficient or no slope)
  • sagging that disrupts the slope
  • no drains or an insufficient number of drains
  • blocked or damaged drains
  • installing drains at high points on the roof

How Drainage Systems Should Work

Drainage from flat roofs usually take the form of gutters and downspouts, internal drains and scuppers.  (A scupper is a drainage device in the form of an opening in a wall, a parapet wall, or a raised roof edge, and is typically lined with a sheet metal “sleeve”.  It allows water runoff to drain into a downspout or leader.  It’s not the same as a drain, which channel water through the deck of the roof and into pipes that carry the water away. If a roof scupper clogs up, it also can cause ponding or leaks.  In a well-designed roof, there are often two sets of scuppers — primary scuppers at the level of the roof membrane, and secondary scuppers that are two inches above the low point, to act as emergency drains in case the primary scuppers become blocked.

Obviously, ponding on a flat roof is a serious problem with several possible implications including:

  • structural damage
  • leaks
  • growth of vegetation
  • reduced life expectancy of the roof

Gutters

Most roofs come equipped with a gutter system.  This is the most popular roofing drainage system.  The goal of a gutter is to drain the water out and away from your property’s foundation for structural protection.

Don’t let the term “flat roof” mislead you into thinking that gutters are not effective for this style of roofing. Though flat roofs are almost level in comparison with their steeply pitched counterparts, they are not completely flat.  They do have very low slopes that allow to them drain water.  Gutters collect the water that naturally falls off your roof into open piping systems.  They then lead the water off and away from your home or building.  Gutters are by far the most cost-effective drainage solution for flat roofs, but they do need to be regularly cleaned and maintained for the best results.

One of the easiest ways to ensure that your gutters stay clean and clear of any debris is to avoid allowing trees or bushes to hang over the top of your roof.  If this is problematic, you’ll find yourself on a ladder cleaning out your gutters frequently throughout the year.

It’s important to note, there may not be a gravitational pull for the water that lands in the center of the roof to direct it toward the gutter system.  There are ways to combat this, but they can get costly.  It’s best to bring in a professional to inspect your roof before making any final decisions.

Interior Drains

Another type of drainage system that works extremely well for a flat roof is an interior drainage system.  This works by placing drains across intervals near the middle of the roof that lead first inside, and then out through a series of gutters and pipes.

The internal network is efficient at reducing the amount of pooling water that often accumulates near the center of the roof.  To prevent any debris from getting trapped inside, interior drainage systems are equipped with strainers.  If you get this type of drainage system, you need to ensure that the strainers are working properly, and nothing is getting through.

Cleaning exterior gutters is time consuming, but easy when compared to cleaning interior drains.  Luckily, this type of cleaning can easily avoided by ensuring your strainers are in place and functioning properly.  The best part about interior drains is the fact that they’re hidden from the outside view of your building.  This creates a seamless aesthetic that’s perfect for both homes and commercial buildings.

The downside to interior drain systems is that when damage does occur, professionals need to be brought in.  While they’re stronger and more protected, they are also inside the building.  When interested in an interior drain system, it’s best to get an accurate estimate for your project. They do tend to be more expensive than other types of draining systems, especially when comparing them to simple gutters.  However, if you’re prepared to commit to an upfront investment, it’ll be well worth your while.

Scuppers

Another potential drainage solution for flat roofs is to install scuppers.  Scuppers are similar to gutters because they are installed along the edge of your roof. However, they work a bit differently.  Unlike gutters, which collect water and lead  it out through a downspout, scuppers work primarily to expel water out and away from the roof.  They’re smaller and don’t line the entire edging of your roof. They’re a bit longer and more strongly angled downward, so that gravity can help push the water off your roof with the momentum needed to keep walls and siding dry.  This momentum also ensures that the foundation of your building isn’t exposed to excess amounts of water.

To get the most out of scuppers, it’s advised to pair them with a roofing system that helps direct pooled water.  This is best done using a tapered insulation system. It’s also possible to achieve the direction you need using a sloped structure; this can, however, can add a lot of excess stress to your roof.

The only downside to using scuppers is snowfall.  They aren’t very efficient in managing melting snow and ice.  Severe weather can also damage scuppers. Otherwise, they are one of the best options for flat roofs.

True Sloped Insulation

True sloped insulation is installed underneath a roof.  It works by utilizing gravity to expel water.  Because of how this is installed, it’s not a great solution for existing buildings, but a viable option for new construction.  True sloped insulation is made out of EPS board, wood fiber board or ISO board thermal insulation. This insulation style must be pre-cut by the manufacturer to the exact measurements of the flat roof.  Professionals then install the slope pattern to create a ramp that guides water away from the flat roof’s surface.

The small slope that’s installed acts as a ramp to avoid any excessive pooling.  It also guides the water off of the surface.  Note, this draining solution is the most expensive option.

Step Sloped Insulation

If you like the idea of true sloped insulation, but don’t want to spend thousands of dollars, you can opt for a step sloped insulation.  The general idea is similar: add a slight slant to your roof to get water off and away.  However, step sloped insulation uses flat board insulation instead of the roof-board that true sloped uses. This is more cost effective because of how it’s installed.  If you’re interested in either insulation option, it’s advised that you contact a professional to schedule an inspection.  Only the professionals will be able to give you the advice you need based on your roof’s specific parameters.

Crickets

 Another important component in the way flat roofs drain is the use of crickets.  A cricket is a triangular structure used to divert water away from certain areas on a roof where it may become trapped, similar to chimney crickets in residential roofing systems.  Crickets are almost always made out of insulation.  The insulation is built up under the roof membrane in such a way that it creates a triangular structure, adding a little more slope to the roof to prevent water ponding.  Roof crickets are usually placed near walls, around HVAC units and skylights, and around drains.  When properly designed, crickets are extremely effective at diverting water where it needs to go to drain off of the roof, and protecting against the issues that come along with standing water.

Central Roof Drains

Central roof drains, also called “inner drains” are often found on commercial roofs.  These drains are placed at the center of a roof, and roof crickets, or the natural roof slope are used to direct water to these areas.  These drains are a particularly good option for very large roofing systems.  They attach to pipes that run down through the building’s roof to carry water down and out of the building safely.  These drains are also a great option for colder climates, because they are not vulnerable to freezing and cracking during the winter since they are protected by the buildings insulation.

Calling in the Professionals

There are a variety of different options when it comes to selecting a drainage solution for flat roofs.  Whether you are thinking about upgrading your current system or selecting one for a new building, it’s best to bring in the professionals.  There are few things worse than a drainage system that isn’t working.  Working with a professional can give you peace of mind and can help you avoid some disastrous problems down the line.