Flat Roof Ponding: What Causes It & How Can You Fix It? | United Roofing

Flat Roof Ponding

Flat Roof Ponding

Flat Roof Ponding in Calgary and EdmontonLook around Calgary or Edmonton and you will see plenty of flat roofs in the commercial and industrial areas.

They are perfect for many businesses in this area – but no roof is maintenance-free.

With flat roofs, ponding of water is a common issue.

If you don’t get to grips with flat roof ponding early on, it can cause bigger problems later on, including expensive water damage to your property.

So, what is flat roof ponding, how do you spot it, and how do you fix problems before they turn into something more serious?

What causes ponding on a flat roof?

Flat roof ponding is when water pools on your roof. This usually occurs after a storm or heavy rain, or when the snow melts.

Contrary to popular belief, flat roofs are designed with a slight slope but we rely more on good drainage and evaporation than simply gravity to run its course.

Unlike sloped roofs, water does not automatically run off flat roofs.

While water will usually start to disappear when the sun comes out, if it lies there for days or weeks, it can start to cause invisible damage to your building.

This is especially true in our climate here in Calgary and Edmonton, with the heavy snow and freezing temperatures.

When these tough weather conditions combine with a drainage problem, there is plenty to be on the lookout for with your roof.

Why is flat roof ponding a problem?

Ponding water should not be left for more than 48 hours once the weather conditions are dry. If it is not addressed, it could damage your roof by:

  • Magnifying the harmful effects of ultraviolet radiation
  • Attracting insects and mould
  • Promoting the growth of vegetation, moss, algae, etc.
  • Gathering unwanted soil, dirt and debris

  • Prematurely degrading the roof membrane, flashings, and coatings

  • Damaging the adhesives and therefore the structural integrity of the roofing system – especially with older built-up and modified roofs

  • Exerting downward pressure on the entire roofing system, potentially leading to roof bowing, sagging, or even collapse

It is highly likely that your roofing installation warranty also requires you to maintain “positive drainage”. It may use other terminology but it means that water should flow off the roof within two days.

Besides that, regular maintenance will prolong the life of your roof and is just good practice for any business premises.


Signs that your roof needs attention

Neglecting the warning signings of flat roof pooling can be a huge (and expensive) mistake.

While a professional roofing inspection will soon pick up the tell-tale signs of pooling, you can perform some simple checks of your roof regularly.

The key things to look out for are:

  • Standing water after wet periods of weather

  • Bowing or buckling of walls or beams (could indicate a serious problem)

  • Cracks in the ceiling

  • Obvious leaks

  • Extreme icicle formation on the roof edges

  • Problems with the roof membrane (on synthetic roofs)

  • Rusting on metal roofs

  • Large blocks of ice forming

  • Visible mould, fungus, or surface vegetation (indicating the permanent presence of water)

  • Blocked or clogged drains (from tree branches or debris) which can prevent water from running off

  • Damaged internal structures such as joists and cracked sealants

  • Problems with the functioning of the HVAC and other electrical systems

Water pooling on flat roof in Calgary and Edmonton

Ponding dirty water on flat roof

In Calgary and Edmonton, a common problem with commercial flat roofs in the winter months is frozen drains.

This often occurs due to pooling water that had accumulated before the temperatures dropped. The water freezes and then, during a chinook, it starts to melt and has nowhere to go – so it ends up pooling on the roof and leading to the types of problems we see detailed above.

If the water constantly freezes and thaws, it can easily penetrate cracks and crevices on the roof, causing further problems.

Tips for fixing flat roof ponding and protecting your roof

A little ponding is usually not too serious on a flat roof but if it lasts more than 48 hours you need to check for underlying problems and damage.

If the problems are not solved by self-inspection and a little basic maintenance like removing debris from drains, it’s time for a professional opinion on how to fix the problem before it grows into a bigger issue.

Sometimes, when a roof is poorly installed, there is too much roofing material on the edge of the roof or the flashing is not installed correctly.

This means that water cannot run off effectively and it will need to be fixed by roofing professionals like United Roofing Inc.

If the drains are frozen, a professional will make sure that the seals around the drains are properly sealed and watertight, so that water cannot penetrate elsewhere.

In extreme cases, you may have to hire a steam truck to melt the ice.

Fix flat roof ponding in Calgary and Edmonton

Sometimes, water from melted snow works its way to the edges of your roof and re-freezes. This causes “ice dams” to form which can create further problems with ponding water.

Insulating your roof properly will prevent the heat in your home from melting the snow on the roof and causing this problem.

Weatherproof roofing membranes usually cover flat roofs. If well-maintained these can last many years. Any problem with the membrane caused by ponding water should be professionally fixed as soon as possible.

Make sure that any ponding repairs on your flat roof are performed only by licensed professionals.

Preventative steps for taking care of your flat roof

Winter is especially tough on roofs. As you’ve seen, many problems occur when snow accumulates on flat roofs.

Consider taking the following measures to protect and avoid damage to your roof:

  • Run regular inspections to check drainage, debris accumulation, structural integrity, etc.
  • Clean gutters and drain spouts of leaves and other debris so that they are not clogged during snowmelt

  • Keep your roof as clear as possible from snow and ice, taking care not to damage pipes and vents when you clear it

  • If “ice dams” start to form, remove them immediately to prevent water gathering and ponding

  • Choose suitable de-icing/meting products for your type of roof membrane

  • Make sure that you insulate your roof effectively

  • Determine the maximum amount of snow that your flat roof can hold without creating problems (this will depend on roof thickness, materials, etc. and can be determined by a professional)

Flat roof ponding problems?

If water is ponding on your flat roof in Calgary or Edmonton, don’t leave it. The problem is unlikely to just go away and it could develop into a larger, more expensive issue.

If you own a retail or industrial building, office tower or apartment building with a flat roof, a licensed professional at United Roofing Inc. can visit your premises and inspect your roof.

We will provide a report outlining any ponding problems or other issues and, if repairs or preventative maintenance are required, we will prepare a quote.

Need more information about installing a flat roof in Calgary or Edmonton? Book a free consultation with us.