Modern flat roofing provides property owners with several dependable material choices.
EPDM rubber, GRP fibreglass and high-performance felt can all form effective waterproof coverings when they are correctly specified, installed and maintained.
There is no single product that is best for every building. Roof size, shape, access, movement, drainage, appearance and budget all influence the decision.
Understanding the basic differences can help homeowners and businesses have a more informed conversation with their roofer.
What Is EPDM Roofing?
EPDM is a flexible synthetic rubber membrane used on flat and low-slope roofs.
It may be supplied in large sheets, allowing some roofs to be covered with relatively few field seams. The membrane is bonded or mechanically secured using a system appropriate to the roof and manufacturer.
EPDM is commonly considered for:
- Home extensions
- Garages
- Dormer roofs
- Garden buildings
- Commercial roofs
- Refurbishment projects
Its flexibility allows it to accommodate normal temperature changes and limited building movement.
Homer Roofing installs EPDM as one of its modern flat roofing options.
Benefits of EPDM
Potential advantages include:
- Flexible membrane
- Large sheet sizes
- Relatively low weight
- Neat appearance
- Suitability for a range of roof sizes
- Straightforward maintenance
- Repair options where damage is localised
EPDM can be especially attractive on a simple rectangular roof where a large membrane can reduce the number of joints across the main surface.
However, the quality of details around corners, outlets, edges and penetrations remains essential.
A large sheet does not remove the need for careful installation.
Points to Consider With EPDM
EPDM may not be the automatic choice where:
- The roof has many complicated details
- The deck is unsuitable
- There is frequent uncontrolled foot traffic
- Previous coatings affect adhesion
- Appearance at edges is a major consideration
- The roof is intended as an occupied terrace
Sharp objects, dropped tools and later contractors can puncture a membrane.
Where access is needed for maintenance, suitable walkways or protection may be recommended.
What Is GRP Fibreglass Roofing?
GRP stands for glass-reinforced plastic, commonly called fibreglass roofing.
The system is normally formed using resin and reinforcing mat applied over a suitable prepared deck. Once cured, it creates a hard, seamless surface that is finished with a protective topcoat.
GRP is commonly used on:
- Extensions
- Garages
- Bay windows
- Dormers
- Porches
- Smaller commercial roofs
- Roofs with detailed shapes
It can provide a crisp, clean appearance with formed edges and trims.
Benefits of GRP
Potential advantages include:
- Seamless surface across the main roof
- Hard finish
- Neat edge details
- Suitability for complicated shapes
- Range of finish options
- Local repair possibilities
- Good resistance to normal weather exposure
Because the system is formed on site, it can be worked around certain corners, outlets and details.
The deck preparation and installation conditions are particularly important.
Points to Consider With GRP
GRP must be installed onto a suitable, stable deck.
Poorly prepared joints or excessive deck movement can contribute to cracking.
Installation may also be affected by:
- Rain
- Low temperatures
- High moisture
- Incorrect resin mixing
- Unsuitable decking
- Contaminated surfaces
- Poor detailing
The roof should not automatically be treated as a balcony simply because GRP forms a hard surface.
Regular foot traffic or occupied use requires a system designed for that purpose, together with structural and safety considerations.
What Is Modern Felt Roofing?
Modern flat roofing felt is very different from the basic shed felt many homeowners may recognise.
Professional high-performance felt systems commonly use reinforced bituminous membranes installed in more than one layer.
Depending on the specification, the system may include:
- An underlay
- A cap sheet
- Reinforcement
- Mineral or smooth finishes
- Torch-applied, self-adhesive or other installation methods
Felt remains widely used on domestic and commercial flat roofs.
Homer Roofing supplies and installs modern felt alongside EPDM, GRP and other roofing systems.
Benefits of Modern Felt
Potential advantages include:
- Familiar and established system
- Suitability for many roof shapes
- Strong multi-layer construction
- Straightforward local repairs in suitable areas
- Range of finishes
- Competitive installation cost
- Compatibility with many traditional flat-roof details
A mineral-finished cap sheet can provide a recognisable traditional appearance.
The multi-layer approach can create a robust waterproof covering when installed correctly.
Points to Consider With Felt
Felt quality varies significantly.
A professional reinforced system should not be compared directly with a basic single layer sold for a small garden shed.
The installation method also matters. Torch-applied systems involve heat and should be installed by trained professionals using suitable safety procedures.
Potential defects on ageing felt roofs include:
- Blistering
- Cracking
- Open laps
- Surface wear
- Splits
- Failed edge details
Regular inspection can identify local issues before they develop into larger leaks.
Which System Looks Best?
Appearance is subjective.
EPDM usually provides a smooth, dark membrane finish. GRP can create a hard, uniform surface with defined trims. Felt often has a mineral-textured finish.
Consider how much of the roof can be seen from:
- Upper-floor windows
- Neighbouring properties
- The garden
- The street
- Adjacent rooms
Edge trims, wall junctions and outlet details can influence the finished appearance as much as the main material.
Ask to see examples of previous installations where possible.
Which System Is Best for a Large Roof?
The best material for a large roof depends on more than area.
The roofer should consider:
- Number of penetrations
- Building movement
- Roof shape
- Drainage
- Access
- Substrate
- Expansion requirements
- Commercial activity
- Installation programme
EPDM and single-ply systems may suit large simple areas, while felt remains widely used on many commercial roofs. GRP may be particularly useful on selected smaller or more detailed areas.
The final recommendation should be made after inspecting the actual property.
Which Is Best for a Garage or Extension?
All three systems can be suitable for garages and extensions.
EPDM may suit a straightforward roof requiring a flexible membrane. GRP may provide a neat, hard finish on a smaller roof with formed trims. Felt may provide a dependable and cost-effective multi-layer solution.
The decision should also account for:
- Whether the garage is heated
- Insulation requirements
- Rooflights
- Parapet walls
- Nearby trees
- Expected access
- Existing deck condition
- Budget
A well-installed suitable system is more important than choosing a material because it is currently fashionable.
Repairability
Accidental damage can happen to any roofing system.
EPDM may be repaired using compatible membrane and accessories. GRP can often be prepared and laminated locally. Felt may be repaired with compatible felt or another approved system.
The success of a repair depends on:
- Condition of the surrounding material
- Moisture
- Surface preparation
- Compatibility
- Extent of the damage
- Age of the covering
General-purpose sealant should not be assumed to provide a permanent repair on every material.
Insulation and Warm-Roof Construction
The waterproof covering is only one part of the roof.
When a flat roof is replaced, it may also be appropriate to review:
- Insulation
- Condensation control
- Ventilation
- Deck condition
- Vapour-control layers
- Roof falls
- Drainage
A warm-roof arrangement commonly places insulation above the structural deck, helping keep the deck warmer and reducing certain condensation risks when correctly designed.
The complete build-up should suit the property rather than simply placing a new membrane over an unknown existing construction.
Consider Future Access and Equipment
Tell the roofer whether the roof will support or provide access to:
- Solar panels
- Air-conditioning units
- Aerials
- Satellite equipment
- Rooflights
- Maintenance routes
- Plant equipment
Suitable supports and protective measures can be incorporated into the design.
Later contractors should not drill directly through a finished roof or leave heavy equipment resting on the covering without agreement.
Ask About Installation Conditions
Different systems have different weather and temperature requirements.
Roof work may need to pause during rain, strong winds, excessive moisture or unsuitable temperatures.
A responsible contractor will protect the property and avoid installing materials in conditions that could affect performance.
This is one reason why planning flat-roof work during August can be beneficial, although British weather can never be guaranteed.
Is Single-Ply Another Option?
Homer Roofing also works with single-ply membranes.
These are flexible sheet systems commonly used on various commercial and larger flat-roof applications.
A roofer may recommend single ply where the roof size, design or project requirements make it more suitable than EPDM, GRP or felt.
The available options should be compared rather than limiting the decision before the property has been inspected.
Choose the System That Suits the Roof
EPDM, GRP and felt all have valid applications.
The right choice depends on the building, not a simple ranking of materials.
Homer Roofing provides a tailor-made supply-and-fit service and works with modern flat-roof systems throughout South London and Surrey.
Explore Homer Roofing’s new flat roof services or contact the team on 020 8641 1234 for a free, no-obligation quotation.