Choosing the right flat roofing system for your commercial building is a decision that will impact your maintenance budgets, operational continuity, and property value for decades. With multiple options available—each with distinct advantages and limitations—facilities managers and property owners need clear, unbiased information to make the right choice.

This comprehensive comparison examines the three most popular flat roofing systems in the UK: traditional felt, EPDM rubber membrane, and GRP fibreglass. We’ll explore their performance, costs, longevity, and suitability for different commercial applications to help you make an informed decision.

Understanding the Three Main Systems

Traditional Felt Roofing (Built-Up Roofing)

Traditional felt roofing, also known as built-up roofing (BUR), has been the standard for UK flat roofs for over a century. The system involves laying multiple layers of bitumen-impregnated felt, bonded together with hot or cold adhesive, and typically finished with stone chippings or a mineral surface.

Modern felt systems have evolved significantly, with torch-on applications and polymer-modified bitumen offering improved performance over older three-layer felt systems.

EPDM Rubber Membrane

EPDM (Ethylene Propylene Diene Monomer) is a single-ply synthetic rubber membrane that has gained substantial market share in the UK over the past two decades. The material comes in large sheets that are bonded to the roof deck and seamed together, creating a waterproof covering.

EPDM has become increasingly popular for both new builds and refurbishment projects due to its durability and relatively straightforward installation.

GRP Fibreglass (Glass Reinforced Polyester)

GRP roofing involves applying layers of liquid polyester resin and fibreglass matting to create a seamless, solid surface. The system is cold-applied and creates a completely watertight covering with no seams or joints that could potentially leak.

Originally developed for marine applications, GRP has proven itself in demanding environments and is increasingly specified for commercial roofing projects.

Lifespan and Longevity

Traditional Felt Roofing: 10-20 Years

Standard three-layer felt systems typically last 10-15 years in UK conditions, whilst high-performance torch-on systems with polymer-modified bitumen can achieve 15-20 years with proper maintenance. The material’s vulnerability to UV degradation, temperature cycling, and standing water means replacement is often necessary within two decades.

Longevity factors:

• Quality of materials used (standard vs high-performance bitumen)
• Installation method (torch-on typically outlasts pour-and-roll)
• Surface protection (mineral surface or chippings extend life)
• Drainage efficiency (ponding significantly reduces lifespan)
• Maintenance frequency (regular inspections catch problems early)

EPDM Rubber Membrane: 30-50 Years

EPDM offers exceptional longevity, with properly installed systems regularly achieving 30-40 years of service, and some manufacturers claiming up to 50 years under optimal conditions. The material’s resistance to UV radiation, ozone, and temperature extremes means it degrades much more slowly than traditional felt.

Longevity factors:

• Membrane thickness (1.2mm vs 1.5mm affects durability)
• Quality of seaming and detailing (weak points if poorly executed)
• Substrate preparation (proper adhesion is critical)
• Protection from foot traffic (walkway pads recommended)
• Ballasting vs fully adhered (ballasted systems may shift over time)

GRP Fibreglass: 25-35 Years

GRP systems typically deliver 25-30 years of service, with some well-maintained installations exceeding 35 years. The seamless, solid surface is highly resistant to cracking and weathering, though UV exposure can degrade the gel coat finish over time, requiring top coat renewal.

Longevity factors:

• Resin quality and proper mixing ratios (critical for durability)
• Laminate thickness (adequate layers prevent pinholes)
• Quality of detailing at upstands and edges
• Top coat maintenance (recoating every 10-15 years extends life)
• Substrate stability (movement can crack the rigid surface)

Installation Complexity and Time

Traditional Felt Roofing: Moderate Complexity

Installation time: 2-5 days for a typical 100m² commercial roof

Felt roofing installation is well-established in the UK, with thousands of qualified contractors available. Torch-on application requires skilled operatives and hot works permits, whilst cold-applied systems are less demanding but may have reduced performance.

Requirements:

• Multiple layers applied sequentially
• Hot works monitoring for torch-on systems
• Weather-dependent (cannot install in wet conditions)
• Edge detailing and flashing work required
• Final surface dressing (chippings or mineral surface)

Complexity factors:

• Fire safety protocols for hot works
• Proper overlap and seaming of layers
• Achieving consistent coverage
• Working around penetrations and upstands

EPDM Rubber Membrane: Low to Moderate Complexity

Installation time: 1-3 days for a typical 100m² commercial roof

EPDM installation is relatively straightforward for experienced contractors, with no hot works required and fewer layers to apply. However, proper substrate preparation and seaming techniques are critical for long-term performance.

Requirements:

• Substrate must be smooth, clean, and dry
• Membrane bonding (fully adhered or mechanically fixed)
• Seam taping or vulcanisation at joints
• Edge and penetration detailing
• Ballasting (if mechanically fixed) or full adhesion

Complexity factors:

• Achieving wrinkle-free installation
• Proper seaming (weak point if done incorrectly)
• Working around complex roof shapes
• Ensuring complete adhesion coverage

GRP Fibreglass: High Complexity

Installation time: 3-6 days for a typical 100m² commercial roof

GRP installation requires specialist skills and precise timing. The resin must be applied and laminated within specific temperature and humidity ranges, and each layer must cure properly before the next is applied. This makes it the most technically demanding of the three systems.

Requirements:

• Multiple coats applied in sequence with curing time between
• Precise resin mixing (catalyst ratios critical)
• Fibreglass matting properly consolidated
• Top coat application for UV protection
• Edge details and upstand work
• Weather-dependent (temperature and humidity critical)

Complexity factors:

• Specialist skills required
• Cannot rush the process (curing times must be respected)
• Quality control throughout application
• Getting details right at first pass (difficult to patch)

Cost Comparison

Initial Installation Costs

Traditional Felt Roofing: £40-£70 per m²

• Standard three-layer felt: £40-£50 per m²
• High-performance torch-on: £55-£70 per m²
• Additional for complex details or access

EPDM Rubber Membrane: £80-£120 per m²

• Standard 1.2mm membrane: £80-£95 per m²
• Premium 1.5mm membrane: £100-£120 per m²
• Varies with adhesion method and specification

GRP Fibreglass: £90-£150 per m²

• Standard specification: £90-£110 per m²
• Heavy-duty specification: £120-£150 per m²
• Higher for complex shapes or detailing

Note: Prices include materials, labour, and standard edge details. Additional costs for insulation, decking replacement, or complex access requirements will apply.

Whole-Life Cost Analysis

Looking beyond initial costs reveals a different picture when considering lifespan and maintenance:

Traditional Felt (20-year period):

• Initial installation: £5,000 (100m² at £50/m²)
• Maintenance (annual inspections, minor repairs): £3,000
• Total: £8,000
• Cost per year: £400

EPDM (20-year period, lasting to 40 years):

• Initial installation: £9,500 (100m² at £95/m²)
• Maintenance (minimal): £1,000
• Total: £10,500
• Cost per year: £525 (but only halfway through lifespan)
• Projected cost per year over 40 years: £263

GRP (20-year period, lasting to 30 years):

• Initial installation: £10,000 (100m² at £100/m²)
• Top coat renewal (year 15): £1,500
• Maintenance (minimal): £1,200
• Total: £12,700
• Cost per year: £635 (but only two-thirds through lifespan)
• Projected cost per year over 30 years: £423

Long-Term Value Proposition

When viewed over their full lifespans, EPDM emerges as the most cost-effective option, followed by GRP, with traditional felt being the most expensive despite its lower initial cost. For commercial buildings where budget planning extends decades, this whole-life perspective is crucial.

Performance in UK Climate Conditions

Temperature Tolerance

Traditional Felt:

• Becomes brittle in cold weather
• Softens in extreme heat
• Vulnerable to freeze-thaw cycling
• Thermal movement causes stress at seams

EPDM:

• Excellent low-temperature flexibility (down to -40°C)
• Stable in high temperatures (up to 120°C)
• Natural elasticity accommodates thermal movement
• No degradation from freeze-thaw cycles

GRP:

• Stable across wide temperature range
• Rigid structure less affected by thermal cycling
• Can become brittle in extreme cold (rarely an issue in UK)
• Excellent heat resistance

Water Resistance and Drainage

Traditional Felt:

• Multiple layers provide redundancy
• Vulnerable to standing water
• Seams and overlaps are potential weak points
• Chippings help with drainage but can block outlets

EPDM:

• Excellent water resistance
• Tolerates ponding better than felt
• Large sheets minimise seam count
• Smooth surface promotes drainage

GRP:

• Completely seamless waterproofing
• Excellent ponding resistance
• Smooth surface aids drainage
• No weak points for water ingress

UV Resistance

Traditional Felt:

• Mineral surface provides UV protection
• Unprotected bitumen degrades rapidly
• Chippings offer reflective benefits
• Requires surface protection throughout life

EPDM:

• Inherently UV-resistant (carbon black filler)
• Minimal degradation over decades
• No surface treatment required
• Dark colour absorbs heat (can be an issue)

GRP:

• Gel coat provides UV protection
• Top coat may degrade over time
• Requires recoating every 10-15 years
• Light colours available for heat reflection

Wind Uplift Resistance

Traditional Felt:

• Good when fully bonded
• Multiple layers provide weight
• Edge details critical for wind resistance
• Chippings add ballast

EPDM:

• Excellent when fully adhered
• Mechanically fixed systems need proper ballasting
• Lightweight membrane requires secure fixing
• Edge details must be robust

GRP:

• Excellent adhesion to substrate
• Rigid structure resists uplift
• Strong bond throughout surface
• Edge detailing highly effective

Maintenance Requirements

Traditional Felt Roofing

Routine maintenance:

• Bi-annual inspections (spring and autumn)
• Clear chippings from outlets and gutters
• Check for blistering or cracking
• Inspect edge details and flashings
• Remove vegetation and moss

Repairs:

• Patch small holes or cracks
• Re-secure lifted seams
• Replace damaged sections
• Re-dress chippings as needed
• Address ponding issues

Maintenance cost: £150-£300 annually

EPDM Rubber Membrane

Routine maintenance:

• Annual inspection
• Clear debris from surface
• Check seams and penetrations
• Inspect edge details
• Verify drainage function

Repairs:

• Patch punctures with EPDM patches
• Re-secure loose seams
• Address mechanical damage
• Clean surface if required

Maintenance cost: £50-£150 annually

GRP Fibreglass

Routine maintenance:

• Annual inspection
• Clean surface (non-abrasive methods)
• Check for any crazing or cracks
• Inspect edge details
• Monitor top coat condition

Repairs:

• Patch small cracks with resin
• Repair damaged areas
• Re-coat surface every 10-15 years
• Address any substrate movement

Maintenance cost: £75-£200 annually (plus recoating)

Suitability for Different Commercial Applications

Office Buildings and Retail Units

Recommended: EPDM or GRP

Office buildings and retail units benefit from long-life, low-maintenance solutions that minimise business disruption. EPDM’s longevity and minimal maintenance make it ideal for properties where roof access is difficult or where budget predictability is important. GRP works well where aesthetics matter or where the roof may be visible.

Avoid felt if: The building will remain in use for 20+ years and you want to minimise lifecycle costs and avoid replacement disruption.

Warehouses and Industrial Units

Recommended: EPDM

Large industrial roofs benefit from EPDM’s quick installation, durability, and tolerance of occasional foot traffic for maintenance access. The material’s resistance to ponding is valuable on large, low-gradient roofs where perfect drainage is difficult to achieve.

Consider felt if: Budget is extremely tight and the roof can be easily accessed for maintenance, or if the building has a limited expected lifespan.

Schools and Public Buildings

Recommended: GRP or EPDM

Educational and public buildings require reliable, long-lasting roofing that won’t need frequent replacement during term time. Both GRP and EPDM offer the longevity needed to align with extended maintenance cycles and budget planning.

Avoid felt if: Replacement would cause significant disruption or if the building is expected to remain in service for multiple decades.

Hospitality and Healthcare

Recommended: GRP

Hospitals, hotels, and care facilities cannot tolerate roof failures or extended maintenance work. GRP’s seamless construction and exceptional reliability make it ideal for critical facilities. The ability to create a completely watertight seal is particularly valuable where water ingress would be catastrophic.

EPDM is also suitable but ensure seaming is carried out to the highest standard and consider fully adhered rather than mechanically fixed systems.

Small Commercial Extensions and Outbuildings

Recommended: Felt or EPDM

For smaller structures, porches, or storage areas, traditional felt may be cost-effective given the smaller scale. However, EPDM’s ease of installation and longevity often make it worthwhile even for small areas.

Consider GRP if: The roof is highly visible or if the structure is complex with many penetrations or unusual shapes.

Environmental Considerations

Sustainability and Environmental Impact

Traditional Felt:

• Petroleum-based bitumen (non-renewable)
• Energy-intensive manufacturing
• Shorter lifespan increases replacement frequency
• Difficult to recycle
• Can off-gas VOCs in hot weather

EPDM:

• Synthetic rubber from petroleum feedstock
• Long lifespan reduces replacement frequency
• Recyclable in some facilities
• Minimal off-gassing
• Dark colour increases building heat gain

GRP:

• Polyester resin from petroleum feedstock
• Fibreglass manufacturing energy-intensive
• VOC emissions during installation
• Long lifespan reduces replacement frequency
• Light colours available to reduce heat gain
• Difficult to recycle

Energy Efficiency

All three systems can be installed over insulation to meet current Building Regulations. However, their thermal properties differ:

• Felt: Dark surface absorbs heat; chippings provide some reflection
• EPDM: Dark rubber absorbs significant heat; white EPDM available at premium
• GRP: Can be finished in reflective colours; reduces cooling loads

For energy-conscious buildings, consider:

• White or reflective EPDM
• Light-coloured GRP finishes
• Green roof systems over waterproofing membrane
• Solar reflective coatings

Common Problems and How Each System Handles Them

Ponding Water

Felt: Highly vulnerable; accelerates degradation; causes blistering EPDM: Tolerates ponding well; minimal impact on lifespan GRP: Excellent resistance; seamless surface prevents ingress

Foot Traffic and Mechanical Damage

Felt: Vulnerable to tears and punctures; chippings provide some protection EPDM: Reasonably resistant but can puncture; walkway pads recommended GRP: Excellent resistance; rigid surface handles traffic well

Seam and Joint Failures

Felt: Common failure point; thermal movement stresses seams EPDM: Properly taped seams very reliable; poor seaming causes most failures GRP: No seams; completely monolithic surface

UV Degradation

Felt: Requires surface protection; unprotected bitumen fails rapidly EPDM: Inherently UV-stable; minimal degradation GRP: Gel coat protects; requires recoating over time

Thermal Movement

Felt: Multiple layers accommodate some movement but seams vulnerable EPDM: Excellent flexibility; accommodates movement without damage GRP: Rigid surface vulnerable to cracking if substrate moves

Making Your Decision: Key Questions to Ask

What is your budget horizon?

• Tight immediate budget: Felt
• Medium-term planning (10-15 years): EPDM or Felt
• Long-term investment (20+ years): EPDM or GRP

What is the building’s expected lifespan?

• Short-term (< 15 years): Felt acceptable
• Medium-term (15-30 years): EPDM or GRP
• Long-term (30+ years): EPDM

How critical is roof reliability?

• Can tolerate occasional issues: Felt
• Needs high reliability: EPDM or GRP
• Mission-critical facility: GRP

What access do you have for maintenance?

• Easy access, can maintain regularly: Felt acceptable
• Limited access: EPDM or GRP
• Very difficult access: EPDM

How important are aesthetics?

• Not visible/not important: Any system
• Visible but secondary: EPDM or Felt
• Highly visible/important: GRP (can be finished to specification)

What is the roof size and complexity?

• Small, simple: Any system
• Large, simple: EPDM (cost-effective at scale)
• Complex with penetrations: GRP (seamless advantage)

What are your environmental priorities?

• Cost-focused only: Felt short-term, EPDM long-term
• Sustainability important: EPDM (longevity) or GRP with light finish
• Energy efficiency critical: Light-coloured GRP or white EPDM

Recommendations by Scenario

Best Overall Value: EPDM Rubber Membrane

For most commercial applications, EPDM offers the best balance of initial cost, longevity, maintenance requirements, and reliability. Its 30-50 year lifespan and minimal maintenance make it the most cost-effective choice over the long term.

Choose EPDM when: You want maximum lifespan, low maintenance, and good value over the building’s life.

Best for Critical Applications: GRP Fibreglass

For hospitals, data centres, hotels, or any facility where roof failure would be catastrophic, GRP’s seamless construction and excellent reliability justify the higher initial cost.

Choose GRP when: Reliability is paramount, aesthetics matter, or the roof has complex detailing.

Best for Budget-Constrained Projects: Traditional Felt

For properties with limited budgets, short expected lifespans, or where regular maintenance is not a concern, traditional felt remains a viable choice.

Choose felt when: Initial budget is extremely limited, the building has a short expected lifespan, or you have easy access for frequent maintenance.

Conclusion

There is no universally “best” flat roofing system—the right choice depends on your specific circumstances, priorities, and budget. However, for most commercial buildings in the UK, EPDM rubber membrane offers the best balance of performance, longevity, and whole-life cost. Its 30-50 year lifespan and minimal maintenance requirements make it particularly suitable for facilities managers seeking predictable, low-maintenance solutions.

GRP fibreglass excels in applications where reliability is critical and where its seamless construction provides peace of mind. Though more expensive initially, its performance justifies the investment for mission-critical facilities.

Traditional felt roofing remains relevant for budget-conscious projects, temporary structures, or buildings with short expected lifespans, but its higher maintenance requirements and shorter lifespan make it increasingly less competitive for long-term installations.

Whatever system you choose, ensure it’s installed by certified, experienced contractors who understand the specific requirements of commercial roofing. Proper installation is at least as important as material selection in determining long-term performance and value.

Before making your final decision, consult with multiple roofing contractors, request detailed specifications, and consider not just the initial cost but the total cost of ownership over your building’s expected lifespan. The few extra pounds spent on a superior system today will pay dividends in reliability, reduced maintenance, and avoided replacement costs for decades to come.