Maintaining Flat Roof

Will a flat roof always leak?

Flat roofs are known as being problematic, with many suffering leaks. However in my own experience the problems with leaking flat roofs are usually as a result of either poor workmanship installing the roof membrane, poor maintenance by the building owner or as a result of age. A well designed and waterproofed flat roof should not cause problems or leak.

Is a flat roof actually flat? No. For clarity, flat roofs actually have a slight slope to allow rain water to drain off the roof, but they seem flat, when compared with more traditional steeply sloped roofs. The slope should be a minimum of 1 in 80, but in practice a minimum slope of 1 to 40 should be used to allow for deflection of the roof and for normal building tolerances.

Why are flat roofs popular? Flat roofs are economical to construct. They reduce the volume of the building thus reducing energy costs and allow, if required, for the roof to be used for other activities like a patio, positioning of services or simply as a green roof.

How long do waterproofing membranes last? The membranes used to cover and waterproof flat roofs usually only last 20 to 30 years. This is less than a well constructed tiled roof. As a result building owners need to plan for replacing the membrane on their flat roofs.

What maintenance is required? Regular maintenance of flat roofs is still required, as they are less forgiving than steeply sloped roofs. The most common problems are that rainwater outlets become blocked with leaves and other windblown debris. Installing leaf guards only slows this occurring as in my experience at this time of year, autumn, even these can become overpowered by the shear quantity of leaves being blown around by the wind.

Why do all flat roofs leak?

Like any roof, in time, after wear and tear and weathering, flat roofs will eventually leak. No roof will last forever and if you have a roof over your head it will most likely leak someday. This is perhaps all the more true of flat roofs, because water doesn’t run off of the roof surface quickly and can easily find breaks in the roofing surface resulting in leaks. Flat roofs are a common feature in many commercial or industrial buildings and often require more work than any other standard types of roofs. Though flat roofs are simple to build, it requires a lot of maintenance and inspection so that everything is functioning as it should.

If you own a commercial property with a flat roof, it can be daunting task to diagnose and resolve a problem if you suspect leakage. Leaks don’t always mean that your entire roof needs to be replaced. The most common and most challenging part of dealing with flat roof issues is figuring out whether you need to get it replaced or if it just needs a few minor repairs. If you notice a leak in your commercial flat roof, call Royal Roofing Ltd. for a complete roof inspection. We will diagnose leaks and repair your roof as necessary.

Common Problems that Can Cause Leaks in Flat Roofs

Flat commercial roofs are more complex than they might seem. There are several common causes for flat roof leaks, and each of them can occur in various situations:

  • Standing water on the roofing surface
  • Roof is located in a harsh environment
  • Utilizing outdated roofing technology

A list of common problems that occur in flat roofs and how to deal with the issues below:

Ponding Water

Standing or “ponding” water is one of the most common issues faced by flat roofs. It is characterized as any water that remains on the roof for longer than 48 hours following precipitation. The longer the water remains on your roof, the greater the chances are that it will lead to damaging leaks. The roof should be designed with a slight slope so that water can easily find its way to the drain points. Sometimes we find that even flat roofs that were carefully designed in this way can eventually be faced with ponding as they age.

It is important that you regularly monitor your roof for any signs of standing water. Gutters, downspouts, wall scuppers and drains will lead to ponding if not functioning properly. Ponding is more likely to occur around large rooftop units because the weight of these structures will prevent the structure of the underlying roofing supports from working as designed, leading to ponding.

Be aware that, even if ponding doesn’t lead to leaks, it still represents a significant roofing problem. The reason for this is, as time goes by,the enormous weight of standing water will gradually make the problem worse. Roof leveling can resolve minor drainage issues, but more serious issues of ponding require changes to the underlying roof structure itself.

Leaks and Moisture

Another common problem with flat roofs is leaks. But since it’s a flat roof, the water doesn’t have anywhere to go but straight down. This means that the moisture can seep into the roof that may cause mold and fungus, or damage to the structure. The best way to overcome this issue is to get your roof inspected regularly so that it can be maintained every time there is an issue.

Damaged Roofing Membranes

Until several years ago, flat roofs were made of multiple layers of asphalt tar, roofing felt and gravel. This was an effective approach, but is time-consuming to install. So, nowadays, roofing membranes are the more popular choice of the business owners. These membranes are made of a very thin single-ply membrane, generally made of durable rubber. In comparison to built-up roofing these membranes are less expensive and easier to install.

But, like any other roofing system, these membranes are prone to damage as time goes by. Cracks, blisters, and splits are some common problems. These cracks and splits allow water to accumulate beneath the membrane and once the insulation becomes waterlogged, it will lead to difficult to identify causes of leaks. For this reason, you should get your roofing membrane inspected regularly for signs of damage.

Cracks in the Roof

Flat roofs tend to have more pressure exerted in comparison to sloped/slanted roofs. When this pressure becomes excessive, it can lead your roof to crack. As soon you see any crack in the roof, call a commercial roofing contractor immediately. Not only will a crack will expose the roof structure – or potentially even the interior of building – to precipitation, but it is also a sign that your roof is structurally compromised and it’s the right time to get it repaired or replaced.


Like most other materials, asphalt flat roofs expand and contract with changing weather. With time, this continued process of expansion and contraction will cause the flashing to pull away from the corners and edges of your roof. The flashing faults will lead to leaks, and moisture can easily get trapped inside the roof. The best way to avoid this is to get your flat roof inspected regularly and repaired as necessary, because if the leaks become significant you will have no other choice except to get a new roof.


Blistering happens when air or moisture pockets get trapped between the layers of the roof membrane or between the membrane and the roof deck.

The pockets expand and stretch the membrane as the sun heats the roof. Unless the blisters show signs of more serious damage, they’re sometimes best left alone. If they’re in an area that is getting foot traffic, the membrane has cracked, the surface is coming off, or the blister is near a seam then they’ll need to be dealt with.

In order to repair a blister in a roof, you’ll need new membrane material that will extend at least six inches around the edges of the blister after it’s been cut out.


Alligatoring is a surefire sign that your roof is aging. The asphalt for your roof has started to age and lose it’s elasticity since the sun’s UV rays have dried the roof material causing it to crack and bubble, resembling alligator skin.

In order to fix a roof that is alligatoring, you’ll need to clean it of particles and dust, then add a compatible primer and lastly, it’ll need a new coating on the roof.

Buckling In The Membrane

The membrane in a flat roof is always one solid piece. As your building shifts and settles, it can cause your roof membrane to buckle and damage the structure. Buckling repair is always best left to a roofing professional.

What are the areas that are common to cause flat roof leaks?

Objects on Flat Roofs: Skylights, chimneys, A/C units, vent pipes, pitch pockets, and other objects contribute to one of the main causes of flat roof leaks. When a skylight seal is broken on the glass, the leak will show in a flat roof itself. When the mortar on the chimney or the chimney crown is cracked, you will find the leak to appear on the flat roof. When an air conditioner unit’s pan is rusted through, it will show a leak on a flat roof.

Where can I expect to find a leak on a flat roof?

Transitions to a pitched roof: Many times an adjacent pitch roof, like an asphalt shingle roof or a cedar roof, will be the reason for a leak on a flat roof. When a shingle roof starts leaking, the water will flow to the bottom of the roof to where the rubber roof is connected, and flow under the rubber membrane causing a leak on the flat roof.

Does materials play a part in Flat Roof Leaks?

Inferior Roofing Materials: EPDM Rubber is the worst roofing material to use for flat roofs. EPDM Rubber Roofs don’t last 10 years without major issues. The adhesives that bond the seams together fail due to extreme heat.