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How to Repair a Leak on a Flat Roof

How to Repair a Leak on a Flat Roof

November 5, 2021

As an owner or operator of a commercial structure, you are faced with many diverse problems when maintaining the building. Keeping the snow shovelled, the grass cut, and other assorted tasks line up with general maintenance. But when you need a flat roof repair, it can be a frustrating dilemma.

Apart from the fact that you are diminishing the value of building because you have problems, the next thing you need to do is find roofing contractors in my area to solve the problem. Local roofing companies can supply roofing services in Toronto, and that is where due diligence is necessary to find the best contractor available.

Repairing a flat roof is also known as a sloped roof repair, and they can be as simple as a patch or as complicated as a membrane replacement for the building. Also, if your building has been subjected to damage from the weather, insurance claims can be complex, and the reconstruction of the roofing system is equally complex hence the need for a proven professional to install a new roof or remediate the damage.

How to Find a Leak on a Flat Roof

When assessing a flat roof for leaks, there are a few details to keep in mind when you set out on your task. The first thing to do is wait for the roof to dry – a three-day span to give the roof time to dry out. During the evening hours, a flat roof will release heat that is stored under the hole, and you will find the ‘hot-spot.’ If this method doesn’t work at your facility, there are a number of other ways to find the problems you need solutions for. When you find a leak, make sure to mark it for future reference as you engage in your problem-solving routine.

Take a measurement from the outside wall to the area in question – a damp or dripping ceiling. If the roof is sloped, you find that there is no ponding damage on the roof above the marker you have in the area of trouble.

Once you have isolated the area, check to see what is installed. Loose flashing or other materials like tar that has cracked can be the source of the problem. The heat of the sun causes expansion and contraction of roofing surfaces, and over time, the process will erode the roof’s flexibility and can create an opening where water can enter your building. Remove all debris from the roof to reveal any potential spots where water can make an entry and look for the roof membrane seams, as they are a source for water entry too.

Another telltale sign of leaks is missing roof nails. They leave small holes that are the entry points for water to enter your building.

Roof gardens are great, but they are a threat to roofs. Water builds up in the plants and causes leaks when it has no way to exit the roof.

If you have had cosmetic roof repairs, like patches or caulking, these short-term fixes may have degraded and now impose the problems they were installed to correct.

If you haven’t located the leak using these methods, get a hose out and start flooding the roof with water. Have a helper inside the building – they will look for water on the ceiling, and you will be able to determine where your problems begin and end.

How to Repair a Flat Roof Leak

Before you set out to repair a leak, the first thing you want to do is clear the roof of all debris. This will help determine the scope of the problem and provide direction for the eventual repair. Now, a few safety tips for repairing the roof, first keep all exit ways open and make sure they aren’t slippery. Wear hi-vis clothing and when using a hose or pressure washer, keep the piping trailer away from you, so you don’t trip over it when working on the roof.


To get to the root of a roofing problem, a thorough inspection must be conducted – start at the edge of the roof and work your way into the centre to get the best results. There are certain areas to concentrate on, and it starts with the drains on the roof. If they are clogged by debris, it will cause water to pond on the roof, and the water will find a way in. Then, look for signs of repair – like patches. They fail, more often than not and are a source of water in your building, as they constitute a temporary fix. Seams are important, and they need to hold fast to protect the inside of the buildings and should be routinely checked. And last but not least, look at the collars and flashings that are inserted on the roof to make sure the seals are strong and holding.

The Repair Cycle

Asphalt Flat Roof Repair

On an asphalt roof, the most common problem is cracks or blisters that are created by moisture embedded in the tar. A quick, emergency fix requires a substance like Rust-Oleum to be applied to seal the opening. In the long term requires the installation of a new roof felt patch that is heated and melded into place.

Concrete Flat Roof Repair

Concrete has been known to crack over time and is the cause of leaks on many buildings with a concrete roof. When inspecting the roof, be sure to remove all the surface wear to find the cracks for repair. For an emergency repair, use a bitumen primer or bitumen-based paint to cover the area for temporary respite. To make your repair permanent, you can torch a piece of roofing felt in place where the crack appears to seal it from the elements.

EPDM, Rubber Roof Repair

Tears and cuts are the banes of this roofing system, and they are the most common problem for a rubber-based roof. Cracks, holes and cuts are the results, and they wreak havoc with your roofing system. Using a lap sealant can fill the gaps, but you shouldn’t use too much in case an extensive repair is required later. For an air of permanence for the repair you need, you can use an EPDM primer that you apply to the area. Once the primer is dry, apply self-adhesive rubber tape – use your judgment when applying tape to make sure you have covered the circumference and then some. Use a roller to spread from the inside out to make sure the hole is filled and patch if tightly affixed to the area.

Felt Flat Roof Repair

The old reliable of roofing systems, this roofing system can be damaged by a puncture from debris, or the felt has aged and is splitting. Leaks at the edging can be problems, as are failing flashings that are part of a roof’s seal. A stopgap fix is an application of a paint solution to fill the holes and cracks. In the long-term, determining how old the roof is, it might be that it has aged out and is no longer viable as protection for the building. If the roof is in decent to good condition, a liquid sealant can be dispersed. If you need to torch on a felt pad, make sure that the contractor applying the solution holds insurance to work with an open flame – it will save a lot of heartache if problems occur.

Fibreglass Flat Roof Repair

The biggest problem a fibreglass roof experiences is cracking around the flashings and at the walls where it is sealed to the building. Damage can also be sustained at the board joints, the trim or at the upstands. The quick fix for any of these problems starts with a soapy water wash and then the application of an acrylic sealant over the crack to seal the opening. For the permanent solution, take acetone and sandpaper and grind down the damaged area. Using a chopped strand mat, you can laminate it in place, then seal it with a resin coating. Make sure to iron out the area to prevent bubbles from forming that will cause openings later. Once you have completed the process, you need to ‘cure’ the area, then apply a topcoat of fibreglass to complete the repair.

Integrity Roofers Offers Quick, Hassle-Free Flat Roof Repair Services

Flat Roof Repair Services As the premier roofing company in the Greater Toronto Area, we at Integrity Roofers want to make your flat roof repair a painless procedure. We have over two decades of service in the business, and our knowledge and experience outdistance the competition. We recommend a roof inspection twice a year, not just to find current problems but to work in a proactive way to identify future problems that you may experience.

If you are having roofing problems – no matter how small – make arrangements to discuss your situation with one of our roofing experts. Should you seek an estimate for problems identified at your facility, fill out the form attached to the link. If you need to speak to one of our representatives in an emergency situation, please call us immediately at Integrity Roofers at 647.953.9365.

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