The Differences Between GRP and EPDM Roofing

Maxwells Roofing installs and repairs both GRP (fibreglass) and EPDM (rubber) flat roofs across Milton Keynes and nearby towns. This guide helps you choose the right system so your roof looks great, lasts, and meets UK Building Regulations—without overspending.

- GRP vs EPDM at a glance:
- GRP: Rigid, seamless laminate with coloured topcoat; excellent for complex detailing and balconies (with anti-slip).
- EPDM: Flexible, often one-piece rubber membrane; fast to install; ideal for larger, simpler roofs.

- Pros and cons:
- GRP: Premium finish, sharp edges, great around skylights/parapets; needs dry conditions; can cost more on large areas.
- EPDM: Quick, cost-effective on bigger spans, high UV resistance; detailing needs expertise; protect from punctures.

- Best uses:
- Extensions/dormers: GRP for visible, crisp finishes; EPDM for simple layouts and value.
- Balconies/terraces: GRP with anti-slip; EPDM works under paving/decking with protection.
- Garages/outbuildings: EPDM usually best value.
- Complex or penetrations: GRP excels; EPDM also works with the right accessories.

- Installation and detailing: Both go onto a sound, dry OSB3 deck. We focus on rooflight kerbs, parapet trims, outlets, and falls to avoid ponding.

- Lifespan and care: EPDM 25–30+ years; GRP 20–30+ years when installed and maintained correctly. Clear gutters, keep surfaces debris-free, and inspect every 12–24 months. Repairs are straightforward for both.

- Costs: EPDM is typically most economical on larger roofs; GRP adds a premium finish on small/medium roofs. Fixed quotes follow a site survey.

- Regulations: We design to Parts A, B, C, F, and L; specify appropriate fire performance (e.g., BROOF(t4) where required); liaise with Building Control when needed.

Why Maxwells: Owner-led quality, 80+ 5-star Checkatrade reviews and 5-star-only Google reviews, fully insured team, fast call-outs. Areas covered include Milton Keynes, Northampton, Bedford, Luton, Stony Stratford, Newport Pagnell, Bletchley, Great Linford, and Bradwell.

Call 07311091804 for free advice and a fixed quote, or email sales@miltonkeynesroofing.uk.

The Differences Between GRP and EPDM Roofing (Milton Keynes Homeowner’s Guide)

Maxwells Roofing installs and repairs both GRP fibreglass and EPDM rubber flat roofs across Milton Keynes and the surrounding area. With 80+ 5-star reviews on Checkatrade and 5-star-only reviews on Google, local homeowners trust us for honest advice, tidy workmanship, and long-lasting results.

Unsure whether GRP or EPDM is right for your roof? This guide explains the key differences – so your roof lasts, looks good, meets UK Building Regulations, and fits your budget.

Call 07311091804 for a free quote or email sales@miltonkeynesroofing.uk.

Overview: GRP vs EPDM at a Glance

  • GRP (fibreglass): A rigid, seamless, fully bonded laminate with a coloured topcoat. Excellent for complex edge details and a crisp, modern finish. Great for balconies when specified with anti-slip. Best for smaller to medium roofs and intricate shapes where you want a premium look.
  • EPDM (rubber): A flexible single-ply membrane, usually in one piece with very few seams. Fast to install, excellent UV resistance, ideal for larger single-span roofs with minimal detailing. Very reliable for garages, outbuildings, and large extensions.

Call 07311091804 for a free quote and friendly advice from a local specialist.

What Are GRP and EPDM?

GRP – Glass Reinforced Plastic

  • Composition: Layers of fibreglass matting saturated with resin, finished with a pigmented topcoat.
  • Finish: Smooth and contemporary, commonly in shades of grey. Custom colours are possible. Can be specified with anti-slip for walkways and balconies.
  • Application: Applied on a dry, prepared deck (typically OSB3), forming a hard, fully bonded shell with crisp edges and trims.

EPDM – Ethylene Propylene Diene Monomer

  • Composition: Synthetic rubber membrane, most commonly 1.14 mm to 1.5 mm thick. Often installed as a single sheet.
  • Finish: Smooth, black finish with neat trim profiles. Can sit under paving or decking on pedestals with the correct build-up.
  • Application: Mechanically fixed or fully adhered to a prepared deck with compatible adhesives. Any seams are taped with specialist accessories.

Pros and Cons of Each System

GRP Pros

  • Seamless, rigid surface with sharp lines and clean trims
  • Excellent for complex details like upstands, rooflights, and parapets
  • Can be specified for pedestrian use with anti-slip topcoat
  • Wide colour choice and premium aesthetics
  • Easy to integrate with neat drip edges and lead-look flashings

GRP Cons

  • Requires very dry, stable conditions for application
  • Can be more time-intensive than EPDM on site
  • Substrate movement must be controlled to reduce hairline cracking risk
  • Typically costs more than entry-level EPDM on larger areas

EPDM Pros

  • Fast installation with minimal seams
  • Outstanding UV and ozone resistance with proven 25+ year performance
  • Flexible membrane accommodates thermal movement well
  • Cost-effective for larger roofs with fewer penetrations
  • Low maintenance and straightforward localised repairs

EPDM Cons

  • Aesthetics limited to black rubber finish, though trims are tidy
  • Complex detailing requires experienced installers and the right accessories
  • Vulnerable to puncture from sharp objects without protection layers
  • Wrinkles can appear if substrate prep or adhesive work is not meticulous

Best Fit by Use Case

Single-storey extensions and dormers

  • GRP: Great for highly visible extensions where a crisp, colour-matched finish is desired.
  • EPDM: Excellent for simple, rectangular layouts where speed and value matter.

Balconies and terraces with foot traffic

  • GRP: Often preferred with anti-slip finish and the correct build-up for pedestrian use.
  • EPDM: Works beneath paving or decking on pedestals with a suitable protection layer to avoid point-loading.

Garages and outbuildings

  • EPDM: Typically the best value and quickest option.
  • GRP: Ideal if you want a smarter finish or added durability at edges.

Large commercial or school roofs

  • EPDM: Often the most cost-effective and fastest solution on uncomplicated spans.
  • GRP: Used for smaller sections or areas with complex detailing.

Roofs with lots of penetrations or skylights

  • GRP: Excellent for intricate detailing by a trained fibreglass installer.
  • EPDM: Works well too when detailed carefully with compatible accessories.

Need tailored advice for your property? Call 07311091804 and we will recommend the best system for your roof, not just what is convenient.

Installation, Disruption, and Detailing

Preparation and decking

  • Both systems should be installed on a sound, dry, level deck. OSB3 is commonly used.
  • We assess existing layers for moisture and structural integrity.
  • Where more than 25 percent of the covering is replaced, insulation upgrades are considered.

GRP installation steps – simplified

  1. Strip and prepare deck. Install new OSB3 if required.
  2. Form trims, upstands, outlets, and falls for positive drainage.
  3. Lay fibreglass matting and resin to create the laminate.
  4. Allow to cure, then apply coloured topcoat. Specify anti-slip for balconies if needed.

EPDM installation steps – simplified

  1. Strip and prepare deck. Install new OSB3 if required.
  2. Dry-fit the membrane, then apply primers and adhesives.
  3. Fully adhere the membrane, roll out, and remove trapped air.
  4. Tape any seams and complete detail work around corners, outlets, and trims.

Detailing that makes the difference

  • Rooflights: Correct kerb upstands, watertight apron detailing, and compatible skylight systems.
  • Parapets and edges: Robust trims, proper drip and kerb profiles, and neat terminations into masonry or leadwork.
  • Outlets and gutters: Correct sizing and positioning to avoid ponding, plus leaf-guards where necessary.

Lifespan, Warranties, and Maintenance

  • Typical lifespans: EPDM 25-30+ years. GRP 20-30+ years when correctly installed and maintained.
  • Warranties: Manufacturer warranties vary by product and thickness. We specify reputable systems with strong aftersales support.

Maintenance tips:

  • Clear gutters and outlets 2-4 times per year, especially after leaf fall.
  • Keep surfaces free from debris and prolonged standing water.
  • Avoid placing heavy or sharp objects directly on the waterproofing. Use protection layers.
  • Schedule inspections every 12-24 months to catch minor issues early.

Repairs:

  • EPDM: Localised patches are straightforward using compatible primers and tapes.
  • GRP: Areas can be abraded and re-laminated. Topcoats can be renewed to refresh the finish.

Cost Guide – Milton Keynes and Surroundings

Indicative supply-and-install pricing depends on access, roof size, substrate condition, insulation requirements, overlays vs full strip, and detailing complexity. As a guide:

  • EPDM
    • Simple small roofs: usually a very cost-effective option
    • Larger spans: economies of scale make EPDM particularly competitive
  • GRP
    • Small to medium roofs: premium finish at a moderate uplift over entry-level EPDM
    • Complex edge detailing or anti-slip balcony systems will increase costs

Because every roof is unique – substrate condition, falls, insulation upgrades, number of penetrations, and edge details – we provide fixed written quotes after a site survey. In most urgent situations we can attend same or next day.

Call 07311091804 for a free site visit and fixed quote.

Building Regulations and Fire Performance – UK

We plan and install flat roofs to align with relevant Approved Documents and industry guidance:

  • Part A – Structure: We assess deck and joists for load and condition, especially if adding heavier build-ups or insulation.
  • Part B – Fire Safety: We specify flat roof systems with appropriate external fire performance. Where required, systems tested to classifications such as BROOF(t4) can be specified. Boundary conditions are considered to help limit fire spread.
  • Part C – Resistance to Moisture: Correct falls, outlets, and reliable waterproofing details are used to prevent water ingress and reduce condensation risk.
  • Part F – Ventilation: Roof build-ups are designed to avoid interstitial condensation. Cold roofs require cross-ventilation. Warm roofs require correct vapour control layers and airtightness at laps.
  • Part L – Conservation of Fuel and Power: If over 25 percent of the roof covering is refurbished, upgrades are usually required to meet current U-values. We advise on warm roof vs cold roof approaches.
  • Building Control: For larger refurbishments or structural changes, we liaise with you and, where needed, with Building Control so your project remains compliant.
  • Competence and materials: We use premium materials from reputable suppliers and follow manufacturer installation guidance to maintain compliance and warranty validity.

Why Choose Maxwells Roofing

  • Local expertise: Based in Milton Keynes and serving Northampton, Bedford, Luton, Stony Stratford, Newport Pagnell, Bletchley, Great Linford, Bradwell, and nearby villages.
  • Owner-led quality: Company owner Luke Maxwell oversees projects for consistent standards.
  • Highly reviewed: 80+ 5-star Checkatrade reviews and 5-star-only Google reviews.
  • Fully insured team using proven methods and tidy site management.
  • Honest, transparent pricing with clear written quotations.
  • Fast response for leaks and urgent repairs.
  • All flat roofing systems covered: EPDM, GRP fibreglass, and felt – plus pitched roof services.

Related services we provide:

  • Flat roof repairs and replacements
  • Skylight and roof lantern installation
  • Gutter cleaning and replacement
  • Chimney repairs and lead flashings
  • Fascia and soffits installation
  • Full roof inspections, including drone where appropriate

Our Flat Roofing Process

  1. Discovery call: We discuss symptoms, roof age, access, and timescales.
  2. Site survey: Visual check, moisture risk assessment, and measurements. Drone if appropriate.
  3. Options and advice: Clear pros and cons of EPDM vs GRP for your exact roof, including insulation and regulation needs.
  4. Fixed quote: Transparent pricing, scope, and timeline.
  5. Installation: Careful preparation, professional installation, and tidy handover.
  6. Handover: Photographs, aftercare guidance, and warranty information.

Questions or ready to start? Call 07311091804 or email sales@miltonkeynesroofing.uk.

FAQs: GRP and EPDM

Which lasts longer – GRP or EPDM?

Both systems typically provide 20-30+ years when correctly specified and maintained. EPDM has an excellent long-term track record for UV stability. GRP excels in rigid, seamless finishes and intricate detail work.

Is GRP better for balconies?

Often yes when it is specified with an anti-slip topcoat and the correct build-up for foot traffic. EPDM can also be used beneath paving or decking with suitable protection layers.

Will I need to upgrade insulation?

If you are refurbishing more than 25 percent of the roof, insulation upgrades are usually required to meet current standards. We will advise on warm roof vs cold roof options and U-values.

Can you repair my existing EPDM or GRP?

Yes. We diagnose leaks and carry out effective repairs to both systems, subject to condition. If a repair is not a good long-term investment, we will explain the options and costs for refurbishment.

Do EPDM roofs wrinkle?

They should not when installed correctly. Smooth finishes depend on good substrate preparation, the right adhesive application, and careful rolling out. We pay close attention to these details.

How quickly can you attend a leak?

We aim for same or next day call-outs across Milton Keynes and nearby towns, weather and workload permitting.

Areas We Cover

  • Milton Keynes
  • Northampton
  • Bedford
  • Luton
  • Stony Stratford
  • Newport Pagnell
  • Bletchley
  • Great Linford
  • Bradwell
  • All surrounding towns, estates, and villages

Get a Free Quote

Ready to choose the right flat roof for your home or extension? Speak to a local specialist who installs both GRP and EPDM and will recommend what is genuinely best for your property.

Call 07311091804 for a free quote or email sales@miltonkeynesroofing.uk. If you are also planning wider works, you may find these pages helpful too: Emergency Roofing, Flat Roof Systems, Roof Repairs, Roof Inspections, and Gutter Maintenance.