Commercial flat roofing installation is a process that looks deceptively simple: a big, flat roof… how hard could it be?! In reality, many things can go wrong with a commercial flat roof installation. Here we'll discuss and explore how to overcome the top three challenges in commercial flat roofing installation.Without the effect of gravity like slope roofs enjoy, there are some unique complexities to flat commercial roofs, especially when it comes to seams and watertightness. The three most important challenges when installing flat commercial roofs are: proper drainage and water management; material selection for weather conditions; and seam and flashing integrity. Here we’ll discuss each challenge in depth, along with the effective solutions for handling them correctly, to ensure the highest integrity for your roof.
Commercial Flat Roofing Challenge 1: Proper Drainage and Water Management
Flat roofs are more prone to water pooling since they lack a natural slope. Improper drainage can lead to leaks, structural damage, and premature roof failure. Solutions include tapered insulation systems, internal drains, and properly positioned scuppers to direct water flow effectively.
Solutions for Proper Drainage and Water Management in Commercial Flat Roofing
Effective drainage is necessary for commercial flat roofs to prevent water pooling, structural damage, and premature roof failure. Here’s a detailed look at three key solutions for good drainage:
1. Tapered Insulation Systems
Tapered insulation systems are designed to create a slight slope on a flat roof, ensuring that water flows toward drains instead of pooling.
How It Works:
- Made from rigid insulation boards with varying thicknesses to create a gradual slope.
- Installed beneath the roof membrane to promote positive drainage.
- Can be customized based on the roof layout and required slope direction.
- Prevents water accumulation, reducing the risk of leaks and structural stress.
- Enhances energy efficiency by adding insulation, reducing heating and cooling costs.
- Compatible with various roofing materials like TPO, EPDM, and PVC.
- Requires precise design and professional installation for optimal performance.
- Can increase upfront costs but leads to long-term savings on repairs and maintenance.
2. Internal Drains
Internal drains are strategically placed in low points of the roof to collect and channel water away through a system of pipes leading to the building’s drainage system.
How It Works:
- Installed at the center or lowest areas of the roof.
- Connected to a network of pipes running through the building to carry water away safely.
- Often covered with strainers to prevent debris from clogging the drain.
Benefits:
- Efficiently directs water off the roof without relying on exterior downspouts.
- Reduces the risk of ice buildup and water damage to exterior walls.
- Aesthetically pleasing since they are hidden within the building.
- Requires regular maintenance to prevent blockages from leaves, dirt, and debris.
- Can be costly to repair if pipes become damaged or clogged.
3. Properly Positioned Scuppers
Scuppers are drainage openings installed in the perimeter walls of a flat roof, allowing water to exit through downspouts or open outlets.
How It Works:
- Cut into parapet walls or roof edges to direct water away from the building.
- Often used in combination with downspouts or splash blocks to control water flow.
- Typically placed at the lowest points along the roof perimeter.
Benefits:
- Provides a simple and cost-effective drainage solution.
- Reduces standing water and helps prevent leaks and roof membrane deterioration.
- Low maintenance compared to internal drains, as they don’t require underground piping.
- Requires correct placement to ensure proper water flow.
- May not be as effective in heavy rainfall if not sized appropriately.
- Can lead to water staining on exterior walls if not paired with proper downspouts.
Each drainage solution plays an important role in ensuring the longevity and performance of a commercial flat roof. Tapered insulation systems improve water flow while enhancing insulation, internal drains offer a hidden yet efficient drainage solution, and properly positioned scuppers provide a cost-effective method for directing water away from the building. A well-designed drainage system helps protect the roof, building structure, and occupants from water damage and costly repairs.
Commercial Flat Roofing Challenge 2: Material Selection and Weather Conditions
Choosing the right roofing material (TPO, EPDM, PVC, BUR, or modified bitumen) depends on climate, budget, and building use. Extreme temperatures, UV exposure, and high winds can impact material longevity and installation quality. Proper installation techniques and high-quality adhesives/sealants are essential to ensure durability and resistance to weather elements.
Selecting the right roofing material for a commercial flat roof ensures durability, weather resistance, and long-term performance. Factors like extreme temperatures, UV exposure, and high winds significantly impact material longevity and installation quality. Additionally, proper installation techniques and the use of high-quality adhesives and sealants are essential for preventing premature failure. Below is a breakdown of these key considerations.
Choosing the Right Roofing Material
Different roofing materials offer varying levels of durability, flexibility, and weather resistance. The choice depends on climate conditions, building requirements, and maintenance expectations.
TPO (Thermoplastic Polyolefin)
Best for: Hot climates with high UV exposure.
Benefits:
- Highly reflective, reducing cooling costs in warm regions
- Resistant to UV rays, ozone, and chemical exposure
- Flexible and impact-resistant, making it suitable for areas with temperature fluctuations
- Heat-welded seams provide superior water resistance
Challenges:
- Can shrink over time if not properly installed
- Adhesion quality is crucial for preventing seam failures
EPDM (Ethylene Propylene Diene Monomer)
Best for: Cold climates with frequent freeze-thaw cycles
Benefits:
- Excellent flexibility in low temperatures, reducing risk of cracking
- High resistance to ozone, UV rays, and weathering
- Long lifespan (up to 30 years with proper maintenance)
Challenges:
- Dark color absorbs heat, which can increase cooling costs in warm climates
- Requires strong adhesives for seam bonding, as heat welding is not an option
PVC (Polyvinyl Chloride)
Best for: High-wind, chemical-prone, and extreme weather areas
Benefits:
- Exceptional chemical resistance (ideal for restaurants and factories)
- Highly reflective surface improves energy efficiency
- Heat-welded seams create a watertight bond
- Superior resistance to high winds and fire
Challenges:
- Can become brittle in extremely cold climates
- Higher upfront cost compared to TPO and EPDM
BUR (Built-Up Roofing) and Modified Bitumen
Best for: Harsh winter conditions and heavy foot traffic
Benefits:
- Multi-layered protection against leaks and extreme temperatures
- Good resistance to wind and punctures
- Durable under heavy rooftop traffic
Challenges:
- Installation can be labor-intensive and costly
- Requires skilled labor for proper application of asphalt layers
The Impact of Extreme Weather Conditions on Roofing Material Longevity and Installation
Extreme Temperatures
High heat can cause material expansion, leading to seam failure in improperly installed roofs. Cold temperatures can make materials brittle, leading to cracks and shrinkage. The solution is to select flexible materials (like EPDM for cold climates) and use adhesives that retain their bonding strength in varying temperatures. Learn more about adhesive heat resistance in our White Paper.
UV Exposure
Prolonged UV radiation can degrade roofing membranes, making them brittle over time. Reflective materials like TPO and PVC help reduce UV damage. The solution is to choose high UV-resistant materials and apply protective coatings if necessary.
High Winds
Strong winds can lift poorly secured roofing membranes, leading to system failure. Wind uplift ratings should be considered when selecting materials. The solution to this challenge is to use high-performance adhesives and proper fastening techniques to secure membranes against wind forces.
Consider Proper Installation Techniques and High-Quality Adhesives/Sealants
Even the best roofing material will fail if not installed correctly or if low-quality adhesives are used. The importance of using high-quality adhesives and sealants cannot be ignored. Adhesives are integral in bonding seams and securing membranes. Low-quality adhesives can break down over time due to temperature fluctuations and moisture exposure. High-performance adhesives should be used to ensure a watertight, durable seal.
Recommended Adhesives Based on Material Type
TPO & PVC: Heat-welded seams are preferred, but high-bond adhesives like Quin QDEK QD2040 or 3M™ 90 High-Strength Spray Adhesive, or Firestone UltraPly TPO Bonding Adhesive can enhance bonding.
EPDM: Requires strong adhesives such as Quin QDEK QD3000 or Carlisle Sure-Seal EPDM Bonding Adhesive for seam security.
BUR & Modified Bitumen: Use asphalt-based adhesives like Henry 203 Roll Roofing Adhesive for superior bonding in extreme temperatures.
Proper Installation Techniques for Maximum Durability
Seam Sealing & Bonding: Ensure seams are fully bonded using heat-welding (for TPO/PVC) or liquid adhesives (for EPDM). Poorly sealed seams are the most common failure point.
Wind Uplift Protection: Secure membranes using mechanical fasteners and high-performance adhesives to prevent wind-related damage.
Moisture Prevention: Properly seal roof penetrations (vents, HVAC units) with polymer-based sealants like Sikaflex® 552 AT or 3M 5200 Marine Sealant to prevent leaks.
Thermal Expansion Management: Allow for material movement by properly spacing expansion joints and using flexible adhesives that won’t crack under stress.
Selecting the right roofing material for a commercial flat roof depends on climate conditions, durability requirements, and maintenance expectations. TPO and PVC perform well in high-heat and UV-exposed environments, while EPDM is better suited for cold climates. High winds require strong adhesives, mechanical fastening, and wind-rated materials. Proper installation using high-quality adhesives and sealants ensures long-term performance, preventing premature failures and costly repairs. By understanding these factors, commercial building owners can make informed decisions that enhance roof longevity and reduce maintenance costs.
Commercial Flat Roofing Challenge 3: Seam and Flashing Integrity
Seams and flashings are the most vulnerable points where leaks commonly occur. Poor adhesion, improper welding, or inadequate sealing can lead to water infiltration. Ensuring proper overlap, heat welding (for single-ply membranes), and reinforced flashing details help to prevent leaks and extend roof life. Addressing these challenges requires skilled labor, high-quality materials, and adherence to industry best practices to ensure a long-lasting, leak-proof commercial flat roof.
Solutions for Seam and Flashing Integrity in Commercial Flat Roofing
Seam and flashing integrity helps prevent leaks, structural damage, and premature roofing failures. Poor adhesion, improper welding, and inadequate sealing are common causes of seam and flashing failures, often resulting in costly repairs and water intrusion. High-performance roofing adhesives play a key role in solving these challenges by ensuring strong, durable bonds that withstand extreme weather conditions.
Seams and flashings are among the most vulnerable areas of a commercial flat roof. Seams join sections of roofing membrane, while flashings provide waterproofing around penetrations (e.g., vents, HVAC units, skylights). Weak seams or improperly sealed flashings can lead to:
- Water infiltration, causing insulation damage and interior leaks.
- Membrane shrinkage and detachment, reducing roof lifespan.
- Wind uplift, increasing the risk of roofing system failure.
Common causes of seam and flashing failures include:
- Poor adhesion from low-quality adhesives or improper application.
- Improper welding of TPO/PVC seams due to incorrect temperature settings or contaminated surfaces.
- Inadequate sealing around penetrations and terminations, allowing water intrusion.
How Roofing Adhesives Solve Seam and Flashing Challenges
High-Performance Seam Bonding with Adhesives
Roofing adhesives ensure seams remain watertight by forming strong, flexible bonds between membrane layers. The choice of adhesive depends on the roofing material:
- EPDM Roofing:
- Requires solvent-based or water-based bonding adhesives (e.g., Carlisle Sure-Seal EPDM Bonding Adhesive).
- These adhesives allow full-surface bonding and maintain flexibility in extreme temperatures.
- TPO & PVC Roofing:
- Primarily use heat-welded seams, but adhesive seam sealants can reinforce areas prone to stress.
- Example: Firestone UltraPly TPO Bonding Adhesive improves seam adhesion in areas where welding is challenging.
- Modified Bitumen & BUR Roofing:
- Use asphalt-based adhesives (e.g., Henry 203 Roll Roofing Adhesive) for durable seam bonding.
- Cold-applied adhesives minimize fire hazards compared to traditional torch-down applications.
Key Benefits of Adhesive-Sealed Seams
- Maintains watertight protection in extreme heat, cold, and moisture conditions.
- Provides superior flexibility, reducing stress-related seam failure.
- Eliminates reliance on mechanical fasteners, which can puncture the membrane.
Proper Flashing Installation with High-Performance Sealants
Flashings are particularly prone to leaks, requiring high-quality adhesives and sealants to maintain waterproof integrity.
Recommended Flashing Adhesives & Sealants
- MS Polymer-Based Sealants (e.g., Sikaflex® 552 AT, 3M 5200 Marine Sealant)
- Ideal for sealing around vents, HVAC units, and parapet walls.
- Superior adhesion to metal, TPO, PVC, and concrete surfaces.
- High elasticity prevents cracking due to expansion and contraction.
- Spray Adhesives for Quick Flashing Installation (e.g., TensorGrip® EP0-CA)
- Speeds up application, reducing labor time.
- Provides uniform adhesion without bubbles or gaps.
Best Practices for Flashing Adhesion
- Clean and dry surfaces before applying adhesives to prevent bonding failures.
- Use primer-based adhesives on porous substrates for better adhesion.
- Apply multiple layers of sealant for high-stress areas prone to movement.
Preventing Seam and Flashing Failures with Correct Application Techniques
Using high-quality adhesives is only part of the solution—proper application is crucial to long-term durability.
Best Practices for Seam and Flashing Adhesion
Surface Preparation
- Remove dirt, debris, and moisture before applying adhesives or sealants.
- Use approved primers on surfaces with low adhesion (e.g., metal flashings).
Application Technique
- Apply adhesives evenly, avoiding gaps that can lead to weak bonds.
- For seam adhesives, use roller application to ensure full membrane contact.
- For flashing sealants, apply in continuous beads and smooth with a tool to eliminate air pockets.
Weather Considerations
- Avoid application in high humidity or freezing temperatures, as some adhesives require dry, warm conditions to cure properly.
- Use cold-weather adhesives (e.g., Lap Sealant for EPDM) in low temperatures to prevent cracking.
Regular Maintenance & Inspections
- Conduct thermal imaging inspections to detect hidden seam and flashing leaks.
- Reapply sealants on aging flashings to maintain waterproof integrity.
Seam and flashing integrity is important for preventing water infiltration and ensuring long-term roof performance. Poor adhesion, improper welding, and inadequate sealing are common failure points that can be addressed with:
- High-performance adhesives and sealants to create strong, flexible bonds.
- Proper application techniques to ensure long-lasting waterproofing.
- Routine inspections and maintenance to detect and repair weaknesses before major failures occur.
By investing in quality roofing adhesives and following best installation practices, commercial roofs can achieve superior durability, reducing costly repairs and extending the lifespan of the roofing system.
