How to Locate Flat Roof Leaks

inspecting flat roof the source of a roof leak can be a challenging task. You may be able to see the water spot caused by a leak, but that doesn’t mean your flat roof leak is right above what you can see. Familiarize yourself with what to look for in order to locate a flat roof leak.

Water follows the path of least resistance, so the leak can essentially be anywhere on the roof. 

Locating the source of a flat roof leak takes a bit of patience, but knowing what to look for greatly helps the process. Start searching for the source once the roof has been dry for a few days.


Start by clearing any debris from the flat roof.

Keep an eye out for places where tree branches or other forms of large debris may have ripped or torn the roofing material. Fallen tree branches can also trap water against the roof and prevent water from draining properly. If you notice tree branches on your flat roof, immediately remove them and carefully inspect the surrounding area.

Check all roof flashing for cracks and damages.

roof vent flashing

Look at all areas of metal flashing. Usually, there are two layers of flashing on flat roofs. The inner layer covers wooden sheathing where it meets protuberances like chimneys, skylights, and vents. The second layer is what can be seen on the outside of the roof and acts as a protective sheet.

These layers need to be able to expand and contract with the roof. If the flashing is rigid and can’t move with the roof, it may allow water to seep below the roof’s coating.

Additionally, inspect all the protection around plumbing vents for any signs of cracking or decay. Any noticeable damage in the collar could allow moisture penetration.

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Don't trust roof patches, and check seam lines.

If your flat roof has recently been patched with roofing caulk or tar, the patch could be the source of the leak.

While roofing tar and caulk can stop leaks, they are temporary solutions at best and tend to fail as time goes on.

Seams in flat roofs crack due to weather and temperature.

Carefully walk along the seams of the roofing material. Look for flaws that might allow for water to come through the roof.

Seams can crack over time due to contractions and expansions due to extreme temperature fluctuations.

Check problematic areas by picking at the edges of the seam with your fingers.


Inspect low areas of the flat roof

flat roof sealant with roller

Walk along your flat roof and look for low spots. If you can’t gauge a lower part of the roof by feel, look for circular watermarks.

Water pools in the lowest parts of a roof and will leave signs once it dries out. Check these areas for any signs of damage or spots where water might seep through.

Pinpoints leaks with a garden hose

Lastly, use a garden hose to troubleshoot any suspicious areas. Spray one section for several minutes and have another person wait inside to notice any drips. If nothing happens, move on to the next section.

This is a time-consuming way to pinpoint the source of a leak, but allows you to determine for 100% where the water is coming from.

And while finding the leak is well within the expertise of many homeowners, performing a lasting repair should be left to a skilled roofing contractor. At Hometown Roofing Contractors, we make it easy to find a qualified roofer for your project. Customers can read up on roofing companies, see what other folks have to say about their services, and compare quotes to get the best price.

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