Weather Safety Series: Don’t Let Extreme Rain Ruin Your Flat Roof

Flat roof with ponding water from extreme rain

Of all of the emergency roof repairs we have done in our 60 years of business in Toronto, the most common is always emergencies caused by water damage. When building owners or property managers ignore the signs of roofing water damage, even a storm that doesn’t seem all that severe could spell disaster for your structure. When it comes to water, the key is to be prepared before the storm happens.

Almost all of the roofing water damage we see is caused by problems that could have easily been avoided with proper inspection, repairs, and maintenance. Here’s how you can protect yourself and your building from some steep repair costs in anticipation of severe rainstorms. 


Positive Drainage Is Essential 

Positive drainage is the most important aspect of the health of your structure. When severe rain storms happen, it is crucial to ensure that the water has a place to go, and is draining effectively. If not, the sheer weight of the water could cause damage to the roof membrane on your building. Even if no structural damage is caused, long term damage from standing water wreaks havoc on the materials of every single roof membrane material, and will almost certainly cause damage. 


The Positive Drainage Checklist 

If your roofing project is a new construction, make sure the design criteria hits all of these crucial markets for rainstorm preparation: 


  • Roof upturns at a minimum of 200mm (8 inches above top of roof membrane). This applies at wall upturns, door and window sills, curbs, plumbing vents, and tall cones among others. 
  • Ask about tapered insulation. Tapered roof insulation, where insulation is cut and fit in a way that moves ponding water towards existing drainage points, is a great solution to help maintain the overall health of any low-sloped roofing system.  
  • If parapet walls are higher than 12 inches, overflow scuppers should be installed to allow optimal water evacuation.


Here are some considerations on existing buildings with in service roofs:


  • Make sure that all drainage points and leaders are clear of debris, including algae or vegetation, that could obstruct the flow of water. 
  • Inspect your roof once or twice per year for positive drainage health and/or water damage.
  • Take note of any changes on your roof that might affect positive drainage in a heavy storm such as any newly installed mechanical equipment, skylights or exhaust vents that are too low to the roof.  Unfortunately, we often find internet cables punched through existing roof vents that are only 1-2 inches above the top of the roof surface.


Don’t Ignore Leaks, Ever

Leaks aren’t just droplets of water coming through the roof membrane, they can show up through older HVAC units and exposed duct work in your building, or start as small issues on the roof that spread into more significant problems at the insulation layers of your roof assembly and cause significant roofing water damage. Wind driven rain in Toronto is usually most severe on the east elevation of buildings. Make sure that occasional leaks through east facing walls are addressed and not forgotten since they only occur infrequently.


Have A Backup Plan 

In the case of a severe rainstorm, having backup items in place for water overflow can ensure the safety of your building and those who reside in it. The best back up plan is to have a secondary relief of water flows in the event that the primary source of drainage is plugged. This could be achieved through the use of proper overflow drains and/or scuppers that are not connected to the storm water system of the building.


Have a Long-Term Maintenance Plan 

When your contractor completes your roof, you should ask for a comprehensive health-plan that will give your roof the best chance for longevity in the long-term. Roofs are not short-term investments, and each element of the structure has a different timeline for checkups and repairs. Have this handy so that you can anticipate inspections, and the costs associated with repairs. 


Heavy rains can do a number on your building, but with the proper protocols and preparations in place, it doesn’t have to spell disaster. If you’re looking for more information on how to protect the health of your roof, check out our blog here, or contact us for more information.