Why do Flat Roofs Leak?

Opinion/ Contact/ Legal

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Who cares why flat roofs leak?

  1. Home Owners

    Naturally the men want to keep the wife happy, and hate the nagging about a leak

  2. Business owners

    Off course they want to keep a la de da profile

  3. Landlords

    Ahh, they would not want to lose a tenant that doesn’t care about their properties

  4. Insurance Companies

    They don’t want to pay for damages caused by leaky flat roofs – mucho dinero

  5. Roofing Contractors

    Hmm, money money money

My thoughts on Flat Roofs in general

Someone mentioned a few days ago “they hate flat roofs because they always leak”.

Why would some people have the idea that “flat roofs always leak”?

I talk from thirty years of experience in dealing with flat roofs only. When I got into flat roofs, I started by fixing leaks on mostly flat roofs on residential buildings. It was not long after I started repairing leaky flat roofs, that I got to install a complete rubber roof. My first two years of flat roofs, repairing leaks and installing new roofs, almost put me out of business. I had so many callbacks on my own jobs that I could almost not keep up with fixing my own mistakes plus trying to do new work to keep head above water.

By taking care of all the flat roof leaks I was responsible for, gave me the best knowledge and experience to understand flat roofs and why they would leak.


A Shingle Roof installed 15% incorrectly will not leak most of the times, whereas a flat roof that is installed 95% correctly will leak 100% of the time
Flat Roofs are unforgiving

Why do flat roofs leak?

Inexperienced Roofers: This is the biggest reason for a leaky roof. During my first two years, I made so many mistakes and did not know anything about flashing, welding seams, material compatibility and why some areas will cause leaks.

What cause flat roofs to leak?

Incompatible roofing materials: There are basically three types of roofing materials used for flat roofs. One can not fix an EPDM Rubber with tar. You can not adhere to Modified Bitumen Torch Down to an EPDM Rubber directly. (I made that mistake) Many tars bought in places like Home Depot are not compatible with Modified Bitumen Rubber.

What is the number one cause of leaks on flat roofs?

Flashing: Most flat roof leaks originate from flashing. Most roof technicians still don’t know how to make a transition from a rubber roof to a metal surface. (flashing)

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.Pitch pocket filled with tar. The pipe leading through the pitch pocket will cause leaks

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.

Skylight flashing causes of leaks
Skylight flashing causes of leaks on flat roofs
EPDM Rubber Transition to a Torch down rubber roof
EPDM Rubber Transition to a Torch down rubber roof with tar. what a mess. No wonder flat roofs leak
Here is a video of aa inexperienced roofer and caused the roof to leak. Cheap is expensive. We lost the bid to this roofing contractor and a year later had to do a new roof over again. This mistake cost the owner over $90,000

I have installed hundreds of roofs in the last 30 years and I very very seldom would get a call back on any roof I have installed. If I do get a callback, then it is normally some issue with something connected to the roof like a chimney, vent pipes and so on.

Flat roofs only leak because of bad workmanship. You hire inexperienced roofers, you more than likely will pay the price of a replacement down the road.


Cheap is expensive

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