How To Repair A Flat Roof Leak


It might seem like fixing a leak on a flat roof would be easy, and sometimes, it is. Sometimes you only need a patch, other times you need to remove a large area and replace it.

Locating the leak can also be a problem. Because the nature of a leak is to travel, just because you have water dripping inside doesn’t mean that the leak will be directly above it.

Steps For Flat Roof Repair

All flat roofs have a slight slant to them that allows water to run off. Before checking for the leak, make sure all debris and obstacles have been removed as they may be covering more damage.

You don’t want to be up on your roof if you don’t know what you are looking for. Hire professionals if you are not sure.

Find The Leak

Ideally, your roof should be completely dry. If possible, let it be for several days after rain or melting snow so it will be easier to find. If you have damp patches or an actual leak, then measure that from the outside wall and it should get you close to where the leak is.

Leaks often happen at seams or where there is something protruding like a chimney, pipe, or vent. Look for missing tiles, nails, and other cracks or small damages that moisture would be able to get through.

If there isn’t a visible or obvious hole or damaged area, it may be coming from a pipe or some place under the roof. This will need a professional to come in and assess the situation.

Repairing The Leak

There are various methods and materials you can use to fix a flat roof leak, depending on what type of roof you have.


Asphalt roofs can be sealed with liquid asphalt. It can be applied with a roller or a brush, depending on how much you need. There are also some products available in a spray-on.

Assuming the damage isn’t too deep, you can make a quick repair. Anything more extensive will need a professional to look at it and make the repairs.


With concrete roofs, leaks are almost always due to cracks. For a smaller issue, you can fill the crack and cover it with more concrete. You can also put sealant over your roof for more waterproofing protection.

Sealing your concrete roof to make it waterproof not only protects it but it can help to extend the life of your roof. Concrete will always have small cracks, but once moisture gets in, damages start to grow.


For a rubber type of roof, leaks often come from tears, holes, and cracks. Rubber roof repair kits are very effective for sealing your roof and repairing and preventing more leaks.

Fill the crack and let it dry. If you think you may need more extensive damage repair, then this will keep it sealed until you can get the professionals to fix it. If that’s all that is needed, seal it with self-adhesive rubber tape.


A fiberglass roof can get cracks almost anywhere but most often around flashings and where it is attached to the building. Once you locate the damage, wash the area and then apply an acrylic sealant over the damage.

For a permanent repair use acetone and sandpaper and smooth down the damaged area. Then with a chopped strand mat, laminate it in place, and seal it with a resin coating.

Hire Professionals

For more serious damages, it is always best to hire a professional roofing contractor. They will inspect your roof to find the damage and let you know if there is potentially any more that you should be aware of.

Keeping your roof clean and in good repair will extend the life of your roof. Inspections are always a smart investment and can help to save you money down the road.

Get your roof inspected twice a year. It’s also to give it the once over after a big storm. Spring and autumn are the perfect times to have a roof inspection. Finding small damages and having them repaired right away keeps your roof in great shape for years to come.

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