Residential Flat Roof Repair Guide

This guide will walk you through the process, from diagnosis to repair options.

Step 1: Diagnosis – Finding the Problem

Before any repair, you must accurately locate the source of the leak. Water can travel far from the actual breach before dripping into your home.

1. Interior Inspection: Go into your attic or the room below the leak. Look for water stains, mold, or dampness on the ceiling and walls. Trace the path of the water upwards to its highest point—this gives you a clue on the roof above.

2. Exterior Inspection (ONLY if safe to do so):

   • Safety First: Use a sturdy ladder and have a spotter. Wear rubber-soled shoes for grip. Do not walk on a wet or very hot roof.

   • Look for Common Failure Points: 90% of flat roof leaks occur at penetrations and seams. Check these areas first:

     • Flashing: Where the roof meets walls, vents, chimneys, or skylights. Look for cracks, gaps, or separated sealant.

     • Drains and Scuppers: Ensure they are clear of debris. Check the seals around them.

     • Seams and Edges: Look for blisters, splits, or open seams in the roofing material.

     • Ponding Water: Areas where water stands for more than 48 hours after a rain. This accelerates wear and tear.

Step 2: Identify Your Roofing Material

The repair method depends entirely on what your roof is made of. The three most common types for residential flat roofs are:

1. EPDM (Rubber Roof): Black or white, sheet-like rubber material. Repairs often involve liquid sealant and special patches.

2. TPO/PVC (Single-Ply): Usually white or light grey, a heat-welded membrane. Professional repair is often best, but some kits are available.

3. Modified Bitumen (Torch-Down or Peel-and-Stick): Looks like rolled asphalt, often with a granular surface. Repairs involve heat (torch) or cold-applied adhesives and patches.

Step 3: Choose Your Repair Method

Here are the most common DIY and professional repair solutions.

A) DIY Repairs for Small Issues

Best for: Small punctures, splits under 2 inches, or failing sealant around flashing.

1. Liquid Roof Coatings / Sealants:

• What it is: A thick, liquid rubberized compound that you brush, roll, or spray on.

• Best for: EPDM and Modified Bitumen. Great for sealing small cracks, covering weathered surfaces, and sealing edges.

• How to Use: Clean the area thoroughly. Apply a primer if required. Use a brush or roller to apply a thick, even coat over the problem area and surrounding few inches.

2. Roof Repair Tape & Patches:

• What it is: A peel-and-stick tape or sheet made of a compatible roofing material (EPDM, TPO, or Aluminum).

• Best for: Quick fixes on seams, flashing, and small punctures.

• How to Use: Clean and dry the area. Cut the tape/patch to size (with rounded corners), peel the backing, and firmly press it down, working out any air bubbles.

3. Roof Cement & Fabric:

• What it is: A thick, asphalt-based mastic used with a fiberglass mesh fabric.

• Best for: Modified Bitumen roofs or small areas where a thick, durable patch is needed.

• How to Use: Apply a layer of cement, embed the fabric into it, and then cover the fabric with another layer of cement.

B) Professional Repairs & Full System Solutions

Best for: Large holes, widespread deterioration, ponding water, or if you’re unsure of the material/repair method.

1. Spot Repair or Patching: A roofer will cut out the damaged section and install a new, properly integrated patch of the same material, often heat-welding or chemically sealing it for a watertight bond.

2. Re-covering: If the existing roof is sound but aged, a new single-ply membrane can sometimes be installed directly over the old one. This is a cost-effective mid-range solution.

3. Complete Tear-Off and Replacement: The most expensive but most reliable long-term solution. The old roof is completely removed down to the deck, which is inspected for rot. A brand-new roofing system is then installed. This is the only way to guarantee a fix for underlying structural issues.

Step-by-Step: A Common DIY EPDM Patch Repair

This is a typical process for a small puncture in an EPDM rubber roof.

Tools & Materials Needed:

• EPDM Rubber Patch (larger than the damaged area)

• EPDM Rubber Roof Cleaner

• EPDM Primer

• EPDM Contact Adhesive

• Seam Roller

• Utility Knife

• Gloves & Safety Glasses

Procedure:

1. Clean: Use the EPDM cleaner and a rag to thoroughly clean the area around the puncture and the back of your patch. Let it dry completely.

2. Prime: Apply a thin, even coat of primer to the cleaned roof area and the back of the patch. Let it become tacky (follow product instructions).

3. Apply Adhesive: Apply a thin, even coat of contact adhesive to both the primed roof area and the back of the patch.

4. Wait for Tack: Allow the adhesive to become tacky to the touch (usually 5-15 minutes). This is a critical step.

5. Apply Patch: Carefully position the patch over the puncture. Once it makes contact, it will be very difficult to reposition. Start from the center and press it down firmly, working outwards to remove air bubbles.

6. Roll: Use a seam roller to apply firm, even pressure over the entire patch, especially the edges, to ensure a strong bond.

7. Seal Edges (Optional but Recommended): Apply a bead of EPDM lap sealant around the edge of the patch and smooth it with a putty knife for a watertight finish.

When to Call a Professional

• The leak is large or the source is untraceable.

• There is significant ponding water (this may require re-decking to fix the slope).

• The roof deck feels soft or spongy (indicating rot).

• The roof is very old and brittle.

• The repair involves torching (modified bitumen) or heat-welding (TPO/PVC), which carries fire risk and requires skill.

• You are simply not comfortable working on a roof.

Cost Estimate

• DIY Repair Kit: $50 – $200

• Professional Spot Repair: $300 – $800

• Professional Re-cover: $4 – $8 per square foot

• Complete Replacement: $8 – $15+ per square foot

Disclaimer: Working on a roof is dangerous. If you have any doubt about your ability to perform the repair safely or correctly, please hire a licensed and insured roofing professional. They can provide a proper diagnosis and a warranty for their work.

What is a Commercial Asphalt Roof?

Typically, this refers to a Built-Up Roof (BUR) or Modified Bitumen (Mod Bit) system. These are multi-layered, durable assemblies designed for large, low-slope (“flat”) roofs.

• Built-Up Roof (BUR): The classic “tar and gravel” roof. It consists of multiple layers (plies) of asphalt-saturated roofing felts alternated with layers of bitumen (asphalt or coal tar pitch), topped with a protective layer of aggregate (gravel or slag) or a mineral surface cap sheet.

• Modified Bitumen (Mod Bit): A more modern version using factory-manufactured rolls of asphalt that has been “modified” with plastic or rubber polymers (like APP or SBS) for increased flexibility, strength, and ease of installation. It is often installed in two layers.

Key Components & Terminology

1. Deck: The structural base (e.g., steel, concrete, or wood).

2. Vapor Retarder: (Optional) A layer to prevent moisture from inside the building from migrating into the roof assembly.

3. Insulation: Rigid boards (e.g., polyiso, EPS) placed on top of the deck for energy efficiency.

4. Base Ply / Felts: The reinforcing fabric layers that form the core of the BUR system.

5. Bitumen: The waterproofing adhesive. Either hot asphalt, cold-applied adhesive, or mastic.

6. Flashing: Sheet metal (or membrane) used to waterproof seams at walls, parapets, drains, and vents.

7. Surface: The top layer, which is either:

   • Aggregate (Gravel): Protects the underlying layers from UV rays and physical damage.

   • Cap Sheet: A mineral-surfaced roll that is embedded in the top layer of bitumen.

   • Reflective Coating: A white or elastomeric coating applied over the surface for UV protection and energy savings.

Common Problems & How to Identify Them

Commercial asphalt roofs are robust but face several common issues:

1. Leaks and Moisture Infiltration:

   • Cause: The #1 problem. Often due to failed flashing, cracks in the membrane, or open seams.

   • Identification: Interior water stains, mold, or drips. On the roof, look for punctures, splits, or deteriorated flashing.

2. Blistering:

   • Cause: Trapped moisture or air between the plies of felts or under the membrane heats up and expands.

   • Identification: Bubbles or raised areas on the roof surface. Do NOT puncture them unless they are already cracked, as this can create a leak.

3. Alligatoring:

   • Cause: Aging and long-term exposure to UV rays and weather, which causes the bitumen to dry out and lose its oils.

   • Identification: A pattern of cracks that resembles alligator skin. This is a sign that the roof is nearing the end of its service life and may need a restoration or replacement.

4. Ponding Water:

   • Cause: Insufficient slope or sagging in the deck, preventing water from draining to scuppers or drains within 48 hours.

   • Identification: Standing water on the roof more than two days after rainfall. This accelerates wear and leads to premature failure.

5. Flashing Failures:

   • Cause: Thermal expansion/contraction, poor installation, or deterioration of sealant.

   • Identification: Cracks, rust, or separation where the roof meets a wall, parapet, or penetration (pipes, vents).

Repair & Maintenance Strategies

The right approach depends on the roof’s condition, age, and budget.

A) Routine Maintenance & Minor Repairs

• Keep it Clean: Regularly clear debris (leaves, branches) and ensure drains, scuppers, and gutters are not clogged.

• Minor Patching: For small punctures or cracks in a Mod Bit or smooth-surface BUR roof, a mastic or asphalt cement patch can be applied, often reinforced with fabric.

• Flashing Repairs: Re-sealing the counterflashing with a high-quality urethane or silicone sealant can address minor leaks.

B) Professional Restoration & Major Repairs

This is where a professional roofing contractor is essential.

1. Roof Coatings (Restoration):

   • What it is: A fluid-applied layer, typically acrylic, silicone, or urethane, that is rolled or sprayed over the entire roof surface.

   • Best for: Roofs with alligatoring or widespread surface deterioration but a sound underlying structure.

   • Benefits: Seals the surface, restores waterproofing, provides UV protection, and can be highly reflective (saving on energy costs). This is often the most cost-effective alternative to a full replacement.

2. Hot Mop / Torch-Down Patching:

   • For BUR or Mod Bit systems, professionals can cut out the damaged section and install a new, integrated patch using hot asphalt (mop) or a propane torch (for APP-modified bitumen). This creates a seamless, welded repair.

3. Re-covering:

   • If the existing roof is structurally sound, a new Mod Bit or single-ply membrane can sometimes be installed directly over the old one. This avoids the cost and mess of a tear-off.

4. Complete Tear-Off and Replacement:

   • The most extensive and expensive option. The old roof system is completely removed down to the deck, which is inspected and repaired. A brand-new roofing system is then installed. This is the only way to address a compromised deck or saturated insulation.

When to Call a Professional Roofer

For any commercial property, engaging a professional is almost always the rule. Call one for:

• Any active leak.

• Widespread alligatoring, blistering, or cracking.

• Significant ponding water.

• Roofing warranty compliance (many warranties require professional maintenance and repairs).

• Safety and liability: Working on a commercial roof involves significant fall risk and requires proper safety equipment and insurance.

Cost Considerations

Commercial roofing is priced by the square (100 sq. ft.) or per square foot.

• Minor Repair: $500 – $2,000

• Roof Coating / Restoration System: $1.50 – $4.00+ per sq. ft.

• Re-cover: $4.00 – $8.00 per sq. ft.

• Complete Replacement: $8.00 – $15.00+ per sq. ft.

Final Recommendation: For a commercial asphalt roof, a proactive maintenance plan with annual inspections by a qualified professional is the best investment. It extends the roof’s life, identifies small problems before they become catastrophic, and protects your valuable asset.

1. Continuing the Conversation: The Roof Lifecycle & Long-Term Strategy

A commercial roof is a long-term asset. Thinking beyond individual repairs to a holistic management strategy is key.

A) The Three Key Phases of a Commercial Roof:

1. Preventive Maintenance & Minor Repairs (Years 1-10):

   • Goal: Maximize the roof’s designed service life.

   • Actions: Biannual inspections (spring and fall), keeping drains clear, promptly addressing small punctures or open seams, and maintaining flashing seals. This is the most cost-effective phase.

2. Major Repairs & Restoration (Years 10-20+):

   • Goal: Delay the massive capital expense of a full replacement.

   • Actions: This is where roof coatings and overlays come in. A restoration system can add 10-15 years of life to a tired but structurally sound roof. It addresses widespread surface wear like alligatoring and ponding water issues with tapered insulation.

3. Replacement & Capital Planning (Year 20+):

   • Goal: Install a new, reliable, and warrantied roof system.

   • Actions: A full tear-off and replacement is a major capital project. It’s the time to reassess insulation R-values, explore different roofing systems (e.g., switching from BUR to TPO), and plan for future rooftop equipment.

B) The Critical Role of a Roof Asset Manager:
For a portfolio of buildings, treating the roof as a financial asset is crucial. This involves:

• Maintenance Logs: Documenting every inspection and repair.

• Lifecycle Cost Analysis: Comparing the long-term cost of restoration vs. replacement.

• Budget Forecasting: Planning for the major expense of replacement years in advance.

3. Exploring a Specific Topic: Roof Coatings in Detail

Since coatings are a critical restoration tool for aging asphalt roofs, let’s focus there.

How Coatings Save an Aging Asphalt Roof:

1. Waterproofing: They form a seamless, monolithic membrane over the entire surface, sealing all the small cracks, alligatoring, and minor imperfections.

2. UV Protection: The sun’s ultraviolet rays are the primary cause of asphalt drying out and cracking. Coatings block these rays, drastically slowing the aging process.

3. Reflectivity: Most coatings are white or reflective, reducing the roof surface temperature by 50-80°F. This lowers cooling costs and reduces thermal expansion/contraction stress on the roof.

Types of Coatings for Asphalt Roofs:

• Acrylic (Water-Based): Most common and cost-effective. Highly reflective and elastic. Best for climates with plenty of sun and rain to wash off dirt.

• Silicone: The king of waterproofing. Stays flexible and ponds water exceptionally well. It is softer and can attract dirt, slightly reducing reflectivity over time.

• Polyurethane/Urethane: Extremely tough and abrasion-resistant. Often used as a top coat over a silicone or asphalt primer for roofs that receive foot traffic.

4. Next Steps and Actionable Advice

What would you like to do next?

• “Tell me more about [Specific Topic]”: Such as roof coatings, how to choose a contractor, dealing with ponding water, or the difference between APP and SBS modified bitumen.

• “I have a specific problem”: Describe the issue (e.g., “I have alligatoring over 60% of my roof and a leak near a drain”), and we can discuss a more targeted strategy.

• “Compare two systems”: We can do a deeper dive into the pros and cons of, for example, a TPO replacement vs. a silicone coating restoration for an old BUR roof.

The world of commercial roofing is vast. Let me know which direction you’d like to go, and we can continue the conversation from there.