A Quick and Easy Leaking Flat Roof Repair Guide

Water can severely damage the integrity of any roof, flat roofs included. If you have noticed a major leak or maybe even several ones, you should act fast if you want to protect your most valuable asset – your home. Sometimes, when a flat roof is leaking, you simply need to patch a small section on the roof but, other times, you will have to replace a roof membrane, which is a quite complex task. Down below, we will be talking more about how to find a leak in a flat roof and how to repair a flat roof leak.

How to Find a Leak In a Flat Roof Within Minutes

Spotting a leak on a flat roof is, kind of, challenging, mostly because the damp spot/dripping area doesn’t necessarily have to be the spot where the leak itself is. Water typically travels across the roof, penetrates the membrane or deck, seeps through, and eventually, shows up on the ceiling.

If this is possible, you should wait for about 2 to 3 days and look up the leak only when your roof is entirely dry. If this is not an option and you are facing an emergency, follow these steps: 

  • Spot the leak area. Try to determine whether ponding of water is or isn’t above this spot.
  • Take a look around and see if there could be something that caused the leak. Look for gaps through which the water can easily seep through, loose metal flashing that needs to be repaired, and other junctions and obstacles as well.
  • Sometimes, missing roof nails or even rusty nails can cause leaks. Other times, it could be that gutters are blocked, which causes floods and leakages and accelerates the deterioration of the roof.
  • Top-layer weaknesses and poorly applied temporary patches can also be the cause of leaks.
  • If you still can’t find the source of the leak, you will have to climb the roof and use a hosepipe to add water manually. It would be best if there was someone who would be checking the inside of the house whilst you are pouring water to the top of the roof. Then, you would have to track the water’s path to determine the place through which the water is flowing into your home.

How to Repair Flat Roof Leaks?

First of all, remove all debris from the roof. Make sure it is not slippery and wear protective clothing and protective gear. Make sure not to trip over pipes or piping trails. Now, here is how to repair different flat roof leaks, depending on different roofing materials.
Asphalt roofing typically cracks or wrinkles because of the high temperatures. Sometimes, it becomes too elastic and saggy, which leaves just enough space for water to come through. To seal gaps, use waterproof fillcoat fibres or apply a small asphalt patch.
To fix concrete flat roof leaks that are also prone to cracking, apply some bitumen-based primer and waterproof paint. This should be enough to seal any cracks.

When it comes to EDPM roofs, cuts, holes, and tears are the most common causes of leaks. To get this flat roof leak repair right, you’ll need to apply small amounts of lap sealant to these tears and holes. Alternatively, apply some EPDM primer to the crack, let it dry, then apply self-adhesive rubber tape on top of the crack. You can also apply a layer of the lap sealant since it is waterproof to really ensure no water can pass through it.

Old felt can easily split or crack, while it also oftentimes suffers from hollows and edging gets loose. You can use a paint-on product to seal cracks temporarily or you can purchase a new layer of felt and refelt some parts of the roof.

Last but not least, to fix fiberglass flat roof leaks, you should, again, seal any splits or cracks, since seasonal extremities can make fiberglass brittle. Wash the entire area and apply acrylic sealant around and on top of the holes and cracks. You can do this instead, too –  sand down the area where the leak is coming from, then install a chopped strand mat under the resing coating, and apply a topcoat that matches the colour of the fiberglass.


Performing a leaking flat roof repair can be a challenging task for people who have never climbed roofs. If you want to get the job done but don’t want to put yourself in danger, hire a professional to inspect the problem and fix it. Groom & Co is a reputable roofing and building company based in London, operating in surrounding areas – Beckenham, Chislehurst, Bromley, and Orpington. Needing any roofing service, make sure to contact us anytime and we’d be more than happy to help.