How to effectively repair a leaking flat roof

A leaking flat roof can be a major concern for homeowners, as it can lead to significant damage if not addressed promptly. Effective repair of a leaking flat roof involves identifying the source of the leak, selecting appropriate materials, and following proper repair techniques. This guide will walk you through the steps to effectively repair a leaking flat roof and ensure its longevity.

Understanding Flat Roofs

Flat roofs, despite their name, are not entirely flat. They have a slight pitch to allow water drainage. Common materials used for flat roofs include asphalt, rubber (EPDM), PVC, and TPO. Each material has its unique characteristics and requires specific repair techniques.

Identifying the Source of the Leak

The first step in repairing a flat roof leak is to locate the source of the problem. This can be challenging because water can travel along the roof’s surface before dripping into your home.

  1. Interior Inspection: Begin by inspecting the interior of your home. Look for water stains on the ceiling or walls, which can indicate the approximate location of the leak.
  2. Exterior Inspection: Once you have an idea of the leak’s general area, inspect the exterior of the roof. Look for visible damage, such as cracks, blisters, or ponding water. Pay special attention to roof penetrations like vents, skylights, and chimneys, as these areas are common sources of leaks.

Preparing for the Repair

Before starting the repair, gather the necessary tools and materials. Depending on the type of flat roof, you may need:

  • Roofing cement or sealant
  • Roofing fabric or patches
  • Utility knife
  • Caulking gun
  • Roofing nails
  • Hammer
  • Ladder
  • Safety gear (gloves, goggles, harness)

Repairing the Leak

For Asphalt Flat Roofs
  1. Clean the Area: Remove any debris or dirt from the damaged area. Use a brush or broom to ensure a clean surface.
  2. Apply Roofing Cement: Using a caulking gun, apply a generous amount of roofing cement to the crack or hole.
  3. Add Roofing Fabric: Cut a piece of roofing fabric to cover the repaired area. Press it into the cement, ensuring there are no wrinkles.
  4. Seal the Patch: Apply another layer of roofing cement over the fabric, extending it beyond the edges to ensure a watertight seal. Smooth it out with a trowel.
For EPDM Rubber Roofs
  1. Clean the Area: Use a mild detergent and water to clean the damaged area. Ensure it is dry before proceeding.
  2. Apply EPDM Primer: Using a brush, apply EPDM primer to the area and let it dry.
  3. Cut and Apply the Patch: Cut a piece of EPDM patch to cover the damaged area. Peel off the backing and carefully apply it, pressing firmly to ensure good adhesion.
  4. Seal the Edges: Use EPDM seam tape or sealant to seal the edges of the patch, preventing water from seeping underneath.
For PVC and TPO Roofs
  1. Clean the Area: Use a suitable cleaner recommended by the manufacturer to clean the damaged area.
  2. Cut and Apply the Patch: Cut a piece of PVC or TPO patch to cover the damaged area. Apply adhesive as per the manufacturer’s instructions and press the patch into place.
  3. Heat Weld the Patch: Use a hot-air welding tool to weld the patch to the roof membrane. Follow the manufacturer’s guidelines for temperature and technique.
  4. Seal the Edges: Apply a bead of sealant around the edges of the patch to ensure a watertight seal.

Preventive Maintenance

Regular maintenance can extend the life of your flat roof and prevent future leaks. Here are some tips:

  1. Regular Inspections: Inspect your roof at least twice a year, ideally in the spring and fall. Look for signs of damage, wear, or potential issues.
  2. Clean Debris: Remove leaves, branches, and other debris that can accumulate on the roof and block drainage systems.
  3. Check Drainage: Ensure that gutters, downspouts, and drains are clear and functioning properly to prevent water buildup.
  4. Trim Overhanging Branches: Trees can cause damage to your roof. Trim branches that hang over the roof to prevent them from falling and causing damage.
  5. Address Issues Promptly: If you notice any damage or potential problems during your inspections, address them immediately to prevent them from worsening.

When to Call a Professional

While many flat roof repairs can be handled by homeowners, some situations require professional intervention:

  1. Extensive Damage: If the damage is widespread or severe, it may be beyond DIY repair.
  2. Structural Issues: If you suspect structural damage to the roof deck or support, consult a professional.
  3. Repeated Leaks: If leaks persist despite your repair efforts, it’s time to call in an expert.

Professional roofers have the expertise and equipment to diagnose and repair complex issues, ensuring the integrity of your flat roof.


Repairing a leaking flat roof effectively requires careful inspection, appropriate materials, and proper techniques. By following the steps outlined in this guide, you can address leaks promptly and maintain the integrity of your flat roof. Regular maintenance and timely repairs are key to extending the lifespan of your roof and preventing costly damage to your home. If in doubt, don’t hesitate to consult a professional roofer to ensure your flat roof remains in optimal condition.