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  • Writer's picturejohndematteo

Ultimate Guide on How To Repair a Leaky Flat Roof

Updated: Jan 16, 2023

Dealing with a flat, leaky roof can be very frustrating. Not to mention the fact that a leaky roof can be extremely detrimental to the overall integrity and value of an asset if not handled properly.

Sometimes it's too late and you may not even realize there's a problem until the inside of the building turns into a swimming pool due to a leaky flat roof.

Find the Leakage

Finding the cause of a leak on a flat roof is usually easier than on a sloping or tiled roof. However, any type of roof leak can be more difficult than it seems.

The first thing you notice water coming into an interior room may not be where the leak is. This is because water that seeps through the roof membrane can travel over the roof until it appears.

However, when you first notice water getting inside, whether it's easy to find or easy to spot, there are steps you can follow to identify the cause of your roof leakage.

Roof Repair Materials

This is the most common type of flat roof repair material.

If you live in the United States, you most likely have one of the following types of roofs:


It is also known as rubber and is a very durable rubber roofing material commonly used in the United States (and around the world). It is mainly manufactured from ethylene and propylene.

Modified Bituminous

Modified bitumen is an asphalt roof made primarily of asphalt with various rubbers and solvents heated by flames using a flared roof covering.


It is also known as a tar and gravel roof. A dense membrane is created using bitumen and reinforcing fabrics.

TPO Roofing

It is a single-layer roofing type made of polypropylene and EPDM that is polymerized together and installed in a fully bonded or mechanically attached system with a white reflective coating.

PVC Roof

This roof is made of two layers of a PVC roof with polyester between the layers acting as reinforcement.

PVC roofing layers contain additives that make the material flexible, UV resistant, and prevent hardening.

What Causes Flat Roof Leaks?

There are many reasons for a flat roof to leak. Common sources include:

Insufficient drainage

If the roof cannot drain properly, water will collect. Over time, stagnant water can erode the roofing material, making the roof vulnerable to leaks.

Old roof

Older roofs are prone to leaks because years of heat, sun, rain, and wind erode the roofing material.

Damaged Flashing

Improperly installed or damaged flashing exposes roof edges to elements, including rain. Poor adhesion can allow water to enter the roof system.

Problematic Roof Membrane

Tears, cracks, holes, shrinkage, and blisters in the roofing membrane make the interior of the roof vulnerable to seepage and seepage.

Stagnant water

Water is heavy, and even small puddles of stagnant water can cause undue stress and wear on flat roofs.

How to Repair a Leaky Flat Roof?

You may want to save money until you have the budget to invest in the necessary repairs to your roof.

Locate the leak

Locate the cause of the leak inside the building. Water may have flowed into the roof through a leak and collected elsewhere.

Multiple measurements are taken relative to the nearest wall in the suspected leak area.

Climbing on the roof

Measure the dimensions from the inside and start looking for leaks in the roof. If there is no visible damage, check the flashing or roof membrane next to the roof vent for damage.

If you must use a ladder to access the roof, make sure it is firmly anchored to the ground.

Remove debris

There may be debris on the roof that can interfere with the operation or cause further damage. Before starting work, carefully remove any debris near the roof leak.

Drainage in the Area

Flat roofs often collect water, so allow the area to be repaired to dry before starting work.

Repairing holes and trapping moisture under the patch can cause mold to form under the roof.

Identify the Damage

Check the roof for blisters. This could indicate water or air seeping between the different layers of the roof.

You'll also want to check for cracks or crocodiles that are usually indicative of long-term sun damage.

Cut off the damaged area

If a roof leak is caused by blisters, carefully cut the damaged membrane and remove any moisture that may be present.

The damaged layer of the roofing membrane must be cut off, but be careful not to damage the roofing material underneath.

Allow the area to be repaired to dry completely before moving on to the next step.

Apply Roof Cement

Peel the layer of the cut membrane and apply roofing cement to the leaking area and the entire roof area under the cut membrane.

Press the membrane flap against the cement to close the incision again.

Flat Roof Repair Costs

Currently, the average flat roof repair cost is $600, with an average range of $250,000. The cost will depend on the cause of the damage, the size, and condition of the roof, the type of roofing material, and the extent of the repair.

The cheapest repair is about $50 for a small area with minor damage.

Extensive damage to a large roof area can cost more than $5,000. Most professional roof repair & Replacement companies charge $3.10 per square foot.

Fiberglass roofs are the least expensive to repair, and metal roofs are the most expensive. Also, some flat roof installation companies charge a minimum fee for emergencies.

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1 Comment

Feb 09, 2022

In rainy season many roofs start leaking. If that's the case you must always contact nearby roof repair company.

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