How do you stop a flat roof from leaking?

Common Issues with Flat Roofing

It is common for commercial structures to have a flat roof, and the reasons are many. The first reason being they are less expensive to install. They are easy to maintain, and flat roof repair and replacement are relatively easier and quick. 

A flat roof also provides a structure more useable square footage, and the HVAC system can be installed on a flat roof, which minimizes vandalism when installed on the ground level. Then there is the concern about the fact that a flat roof leak is highly likely. 

Yes, like anything else, there are downsides to a flat roof, leaks are probably the most significant concern and downside. It seems that flat roofs and leaks go hand-in-hand, but once you have determined what flat roof leaking causes are, you can remedy the situation. 

Do flat roofs always leak?

The first thing you should know is that a flat roof is not genuinely flat. Every roof has to have some slope to it so that it can shed water. On a pitched roof, like on your home, the rain runs off it as it comes dow. It then goes through the gutter system and on to the ground.  A flat roof will have drains installed, and the rain runs from the slight slope to the drain and then on to the ground. 

A flat roof will develop a leak when the drains are clogged because it has nowhere to go. It will pond on the roof, and if it isn’t dried up promptly, it sits and soaks through the membrane.  This is a situation where workmanship can be blamed for a flat roof leak. 

Poor construction and workmanship are too often the culprits for a flat roof leak. During the construction phase and reroof phase, money is typically on a tight budget, understandable. The contractor, during the construction phase, is concerned with being under budget and under time.  Once the building is occupied, it becomes the responsibility of the owner to have regular maintenance to check for a possible flat roof leak and other issues. 

Because ownership of a commercial structure has a budget, he may instruct the maintenance team to do the minimal work necessary to patch the roof. If they deem a seam coming loose or an area with ponding water isn’t a concern, that can allow water to get under the membrane, and the flat roof leak will happen. 

How do you find a leak in a flat roof?

If your flat roof is leaking, to fix it or see what is needed, you first need to find where the leak is, and like on a pitched roof. It isn’t always as simple as the flat roof leak being where the wet spot is on the ceiling.  The following steps will help you isolate where the flat roof leak is located: 

  • Clear all debris, like tree branches or anything that the wind could have blown onto the roof. Look for any gouges or tears. 
  • Check the metal flashing at membrane seams, around pipes and vents, around the HVAC system, along the edges, and in the corners. Note if you see any bent, loose, or missing.
  • Check the collars and flanges around the vents. Look for any cracks or decay. 
  • Look for previous patches with caulk or tar and note if they have cracked or came loose. 
  • Check all the seams, even if there isn’t flashing over them, to see if they have come apart.
  • Look for any low spots on the flat roof for leaks. These can cause water ponding there.

If you notice any problematic areas, these could be potential spots. Using a water hose, run water over those areas for a few minutes and see if the flat roof leak starts. 

How do I stop my roof leaking in heavy rain?

Several factors can cause a commercial flat roof leak. First, you have to understand that every roof has its uniqueness when it comes to strengths and weaknesses. The following are common problems associated with a flat roof leak, and by knowing these are why your roof could be leaking when it is raining, you can take care of the matter and stop it.

Puddles Saturating

Because most commercial rooftops have a flat roof, leaks will happen when the drainage system isn’t working. It is natural to have puddling after heavy rain, but when they last for several days, that usually indicative of a problem. When water is allowed to collect, sit, and saturate a spot, it softens the membrane, the materials under the membrane, and before you know it, you have a flat roof leak. You can stop that flat roof leak by keeping the drains and downspouts clear. 

Flashing Damaged

A common cause of a flat roof leak on a commercial structure is damaged flashing. The purpose of flashing is to seal the roof’s perimeter and seams. It is a protective layer against debris and water, getting past the membrane and roof covering. Heavy, high winds can rip flashing off if it catches a loose spot, and with contracting and expanding with the weather, it will naturally weaken. Monthly inspections and making repairs to flashing when noticed will minimize, if not stop, a flat roof leak in heavy rains.

Membrane Damage

A protective barrier is applied to flat commercial roofs to keep debris, rain, snow, and harsh winds off of the raw roofing material. That outer membrane slides water off toward the drainage system so that it can’t saturate the roof surface. With UV rays and other climate issues, that membrane ages and is weathered, making it susceptible to blistering and cracking. Once that blister pops or a crack is opened, the membrane is no longer doing its job to protect that raw roofing material. The monthly inspection should include looking for these blisters and cracks and either patch them or have the roof recoated to stop any heavy rain flat roof leak.

Pipes and Openings Poorly Sealed

Just like a house, there are pipes on flat commercial roofs, and they usually have the HVAC units and other equipment extending through the surface. There should be adequate seals installed around these roof openings, but once they become damaged or weakened by the climate, heavy rain can get through them and saturate the roofing, damaging the roof and the structure. Again, a monthly inspection should look for these issues and repairs made immediately so that heavy rain doesn’t cause a flat roof leak. 

What can I use to seal a leaking roof?

You’ll need to clean the roof of any debris and dry up any ponding water.  Assuming you have located the flat roof leak, you can use a patching material, like silicone, and apply with a dense brush over the leak.  If the leak is at the flashing, replace the flashing or cover with silicone material.  If the leak is around a vent or the HVAC system, replacing the boot around it is recommended.  

Another option, and probably the best, is to call a professional commercial roofing contractor.  They will have the equipment and experience, and they will know the best patching material for your roof’s membrane. 

In Closing 

We could answer the common question,” Why is my flat roof leaking?” with a harsh reality answer of “Because you haven’t done your monthly flat roof inspections as recommended so that you could catch any of the issues we just mentioned.” We also provide you a simple answer that the three main reasons a flat roof leak happens are:

  • Ponding Water
  • Damaged Membrane
  • Roof Penetration Flashing Loose or Missing

To own a commercial building comes with responsibility, and the flat roof is a big part of your commercial building’s stability. The monthly inspection is recommended, and if not by your maintenance team, then by a professional roofing contractor.