Positive Drainage: Maintaining And Optimizing Your Roof Drains

Positive flat roof Drainage

In our first positive roof drainage article, we talked about what happens when your roof doesn’t have positive drainage mechanisms installed (spoiler alert, it’s not good!). But what happens when you do have a positive drainage system set up, and are still experiencing ponding water issues? Alternatively, what steps can you take to improve roof drainage on your existing flat roof structure? We’ve partnered with Israel Silver of Silver Plumbing to shed some light on the most common roofing drainage problems.

The first thing to look at is the location of your drains. If a knowledgeable professional installed them, the drains should be positioned at low spots on the roof, so that water can drain as effectively as possible. If your drains are in the “right” place and there are still issues, an obstruction of one or more drains is likely the culprit.

There are many reasons why blocked drains can occur, but in our experience, one of these six culprits is usually to blame:

1. Drain Pipe [Rain Water Leader] Blockage:

A blockage inside drains can occur when debris is left on your roof, or when the roof has frequent foot traffic. Israel Silver of Silver Plumbing stated that he has found everything from beverage bottles, tennis balls, gravel, or even portland cement, stuck inside drains causing either a partial or complete obstruction.

2. Frozen Pipes:

In some cases, drain pipes that pass through warm interior surfaces before they discharge outside the wall of a building near grade level can freeze creating an obstruction that prevents the proper flow of water off the roof. This usually occurs when the drainpipe is exposed to freezing conditions and can be remedied by an electrician installing heat tracing wires to keep the pipe’s temperature at 1 degree above Celsius.

Frozen Pipes

3. Backfall and Sagging:

Drain piping inside premises that is not properly sloped to existing rain water leaders can cause inefficient drainage and result in water that remains inside the pipe. This is commonly known as “backfall” or “sagging” according to Part 7 of the Ontario Building Code.  We often see ponding water on the roof around existing roof drains when the interior drainage system is not working.

4. Blocked Control Flow Weirs

In the 1980’s, control flow weirs became mandatory on roof drain assemblies to inhibit the free flow of water into roof drains.  The prime objective of the weirs is to control flooding during larger storms. The problem is, while these narrow slots are effective in metering the flow of water into drains, they can easily get blocked with debris. This scenario cuts off the positive flow of water into the roof drains, and results in ponding water on your roof.

5. Blocked Drain Baskets:

Roof drain assemblies include baskets to prevent objects from getting inside and plugging roof drains. Very often these baskets get blocked with vegetative or other debris cutting off the positive flow of water into roof drains.  It is a paradox that the basket that is used to prevent drains from getting plugged is itself very often the primary source of a blocked roof drain.

6. Narrow Interior Pipes

Buildings that were completed before the mid 1960’s had a combined system of piping for storm and sanitary drainage. There are conditions where the plumbing vent terminal is not up to code (a minimum of three inches wide) or plugged from debris inside the premises, which can cause a backup of water on the roof.

How To Fix Obstructed Roof Drains:

1. Get your roof regularly inspected

It can be extremely difficult to tell what the actual problem is with your drainage system without the help of a professional. Regular inspections of your roof and drainage system are recommended. It is crucial that your inspector pays attention to the roof drainage system both above and below the roof’s surface, to ensure that the drainage system will perform well in the event of a large storm.

2. Check your roof a few days after a big storm

If you do notice any anomalies with your roof, make sure to have it checked out as soon as possible. Many building owners don’t realize just how damaging water can be when left to its own devices on your roof. The best way to gauge the health of your drainage system is to inspect your roof a few days after a large storm. Especially if it’s the summer and the weather is warm, the drains should have done their job. If you notice ponding water at this point, call in a specialist.

3. Make sure Drains are clear of debris

Keep roof drain baskets and control flow weirs clear of any blockages. Make sure that you regularly clean organic and other debris off of your roof to help avoid blockages as well (leaves, branches and other materials).

If you’re noticing that your roof has ponding water, don’t panic! The team at Elite Roofing is here to help with any and all of your roofing needs. We are available 24/7 to make sure your roof is functioning at its peak. Contact us here for more information.