A flat roof, a common type found mostly in older homes, is a slightly 10°slopped roofing system made of EPDM, TPO, bitumen, and other materials. It requires regular water drainage, cleaning, and maintenance to prevent leaks, damage, cracks, or other water damage.

Repairing a flat roof involves carefully inspecting the roof membrane and flashing to find leaks, damage, cracks, or holes. Locate the leaks and apply roof sealant and patch for small leaks. Replace the roof for extensive leaks, especially when dealing with EPDM, TPO, or bitumen roofing materials.

Seek professional help to avoid more damage. You must also know your cost, repair frequency, and longevity to ensure quality repair. I will talk about the steps of How to Repair a Flat Roof.

Who is writing this how-to guide?

I am Altin Collaku, the owner of Gothic Construction, LLC. My father used to work in the roofing industry since 1986, and now I am doing it. I decided to bring a more structured and organized approach to this field by founding Gothic Construction in 2010. This 14 years of experience has taught me a lot of practical things regarding roof repair that a DIYer will not find easily.

With a strong commitment to excellence, I have led Gothic Construction, LLC to achieve awards such as Green Certifications, Seal Certification, ETC, certificates, and licenses, showing my credibility and dedication to this work. I always put my client’s interests at the forefront so they can trust me. My fairness, honesty, and personal responsibility drive me every day toward excellence.

How to Repair a Flat Roof Directions

Identify the damage

I start the repairing process by identifying the damage. Flat roofs have different types of damage, including leakage, cracks, membrane punctures or tears, mildew growth, and drainage problems. Then, follow the steps below to identify the damage.

Leakage

Check for signs of water stains on the ceiling or walls or pooling water on the roof surface. Look for yellowish or brownish rings in your interior ceiling. It clearly indicates infiltrated water through the roof membrane. The stain and leak location will not align directly since water drips some distance.

How to locate the leaks

Locating the leakage area is tricky since the water drips some distance before becoming visible. Follow the steps below to locate the leaks.

• Measure the wet or discolored area from the walls.
• Take a ladder and have a friend hold it for you. Use it and climb onto your roof.
• Now, use the tape and look for a similar area on the roof. You will find the leaks, punctures, cracks, or areas.

Cracks or punctures

Look for clear signs of visible cracks or punctures in the membrane. They are easy to inspect and find.

• Visible Surface Damage: Examine the roof surface around equipment areas, such as HVAC units. Look for tiny holes. They become larger fissures if not addressed.
• Edge and Seam Vulnerabilities: Inspect seams and edges since they are the most vulnerable to separation and cracking for thermal expansion and contraction. Look for small material splits or lifting.

Mildew Growth

Find dark spots,  dark green, black, gray discoloration, or mold on the ceiling or roof. They grow due to moisture buildup and damage to structural integrity. When moisture is trapped within the roofing layers, you will also find a musty odor inside the room.

Drainage Problems

Look for standing water on the roof. It indicates poor drainage since flat roofs are inclined to channel the water away. Check the gutters and downspouts for blockages by debris, leaves, or ice dams. Inspect the roof drains and scuppers to ensure they are positioned and functioning perfectly.

Clean the area

Cleaning the damaged area involves removing debris, dirt, or loose material around the damaged section. Use a tough broom to remove dirt to ensure the repair materials adhere properly.

Dry the area

Dry the area to remove moisture for effective cement or sealant repair. Use a paper towel or propane torch to dry the area. If the weather is sunny, wait a few days to dry out the entire roof. It works better than a towel or propane torch.

How to fix the small cracks or holes on a Flat Roof

Fixing small cracks or holes on a flat roof requires carefully handling the right tools, materials, and methods. Follow the steps below to fix the small cracks or holes.

Step 1: Cut the Blisters and Bubbles

Take a utility knife and cut the blisters from the middle to pop them. Trapped moisture and overheating are the main cause of blisters and bubbles. Make a clear incision without going too deep.

Step 2: Trim Excess Material

Cut away the excess materials around the blisters using a utility knife. Keep cutting until you reach the underneath of the blister. Stop there to prevent puncturing the membrane. It will create a flat surface to patch the leak. If not, cut narrow strips around the blister to level the area. Use a scraper to scrape off any damaged roofing material.

Step 4: Apply Roofing Cement

Take a towel and spread 1/8 inch thick roofing cement over the damaged area. The cement must extend a minimum of 6 inches beyond the perimeter of the damaged area for a secure seal. It will waterproof the gaps.

Step 5: Lay Fiberglass Mesh

Fiberglass mesh improves the waterproof ability. You can also use fiberglass scrim. Measure the area and cut a piece of fiberglass mesh accordingly. Make sure it extends into the surrounding roofing cement. Now, press the mesh into the cement.

Step 6: Cover the Mesh with Roofing Cement

Apply another layer of roofing cement over the fibreglass mesh. Make the mesh invisible with the cement.

Step 7: Sprinkle Gravel for Protection

Sprinkle a layer of gravel over the cement. The gravel shields the patch from UV and other environmental factors.

Step 8: Seal Cracks Along the Edges

Inspect the edges to find any visible cracks. Use a roofing caulk to fill them. It will waterproof the membrane to ensure longevity.

How to patch a membrane on a flat roof

Larger leaks require patching the membrane on the flat roof. Follow the steps below to patch the membrane.

• Collect the right materials such as blow torch, adhesive, and others. Ensure you get the right membrane materials according to the roof materials – EPDM, aka Rubber, Modified bitumen, BUR (Built-up roofing), TPO Roofing, and PVC roofing.
• Consult the manufacturer if you are not sure about the materials.
• Start with cutting and trimming the damaged area. Remove loose materials to create a clean and level surface area for patching.
• Spread a 1/8-inch (0.32 cm) layer of cement and squish cement to the holes or cracks. Push them 2 in (5.1 cm) inside the holes. Level up the cement using a towel.
• Cut the membrane patch according to the damaged area to seal properly.
• Attach the membrane patch and press it firmly so there are no air bubbles or gaps. Use a blow torch to heat and activate the adhesive.
• Spread another layer of cement over the membrane. It has to be level with the rest of the floor.
• Attach another patch larger than the first one by 6 inches in all directions for additional protection.
• Apply another layer of cement and gravel over it.

Process of Resealing the entire roof

When the seal is damaged, it is important to reseal the entire roof. Follow the process below to reseal the roof.

• Clean the roof from debris, dirt, or loose material. Dry it to remove moisture.
• Apply a 1/2-inch (1.3 cm) layer of bitumen primer across the entire roof and dry it completely. Check the manufacturer’s manual for drying time. 1 US gal (3.8 L) is good enough for 100 sq ft (9.3 m2).
• Buy a strip of fiberglass mesh according to your roof size. Unroll it across the roof.
• Cut the mesh for a perfect fit to the area, and make sure the mesh does not have any wrinkles or folds. Secure it with boards or buckets.
• Use a paint broom to apply a 1/2-inch (1.3 cm) thick sealant layer over the mesh in one direction. Mix the sealant before applying it to achieve a smooth consistency.
• Now, unfold the mesh and apply more sealant. Press it into the wet sealant for proper adhering. Cover the mesh completely with more sealant to eliminate any air pockets or gaps.
• Continue the process until each section is overlapped to create a seamless layer.
• Wait for 12 hours to dry the sealant. Then, apply another layer of bitumen sealant for extra protection.
• Inspect the roof after the sealant is dry to find any dips, gaps, or imperfections. Fill them to ensure an even and smooth surface.
• Finally, paint a reflective coating over the roof. It reflects the sunlight to reduce heat absorption and prevent sun damage.

Flat Roof Repairs vs Flat Roof Replacement Options

Get Help From Our Expert Roofers

Repairing a flat roof without prior experience is risky and challenging. Improper repair leads to further damage, leaks, and costly future repairs. Altin Collaku, the Owner of Gothic Construction, LLC,  has 14+ years of experience in roofing services accurately assessing your roof’s condition and providing professional, effective repairs. Our high-quality materials and modern techniques ensure proper flat roof repair and replacement.

How much does it cost to repair a flat roof?

The average cost to repair a flat roof is $700, with $1,100 being the highest and $300 being the lowest.  Repair costs $3 to $15 per sqft (Square foot). However, the cost varies with the material type, labor cost, size, complexity, removal of the old roof, and roof accessibility. The location plays a vital role in determining the cost. Urban areas are more expensive for roof repair compared to rural areas.

What are the causes of a Flat Roof Leaking

The common causes of a flat roof leak are mentioned below.

• Age
• Expired roof
• Solar grain and sudden temperature change
• Blisters
• Damaged flashing
• Poor drainage
• Damaged membrane
• Faulty installation
• Ponding water
• Blocked gutters
• Delamination
• Soffit and fascia damage

When to Repair a Flat Roof

Repair your flat roof when you see the following signs.

• Minor leaks
• Isolated Blisters or Bubbles
• Ponding water
• Cracks, holes, wear, and tear
• Damaged flashing
• Mold or mildew smell
• Mold spots 
• Watermark on the ceiling
• Higher energy bills

How Long Does a Flat Roof Last?

The longevity of a flat roof depends on the material type, proper use, weather, and other factors. Here is a table to understand how long a flat roof lasts.

Safety measurement while repairing a flat roof

“30% of roofing accidents happen due to lack of proper training and supervision. Follow the steps below to ensure safety while repairing your roof.

• Always use Personal Protective Equipment (PPE), such as gloves, safety goggles, non-slip shoes, and a hard hat.
• Always install guardrails, safety nets, or personal fall arrest systems.
• Use a stable ladder. Have someone to hold the ladder.
• Check weather conditions before repairing.
• Use the right tools and techniques.
• Avoid overloading the roof with materials.
• Keep the area clean.

Wrapping up

Repairing a flat roof requires special care and attention to get perfect results. Hire a professional to avoid messing with the roof and waste materials and time. Do it only if you have experience. Start with cleaning the area. Identify and locate the damage. Apply membrane or sealant depending on the damage. Dry them properly and keep the area clean.

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