Flat Roof Types: Which Roofing System Is Right for Your Property?

Felt roofing

Modern felt roofing is a multi-layer bituminous system, a long way from the single-layer mineral felt many people picture. Layers are bonded together and dressed into upstands and outlets to form a continuous covering.

It is widely used on extensions, garages and outbuildings, it handles complex shapes and penetrations reasonably well, and localised damage can usually be patched into the existing covering. Quality depends heavily on the standard of installation at laps and details. See felt roofing.

GRP / fibreglass roofing

GRP is a glass-reinforced polyester laminate applied wet over a prepared deck and cured in place, producing a seamless covering with no joints in the field of the roof. Trims are bonded in as part of the laminate and a topcoat finishes it.

It suits regular-shaped roofs with good deck preparation — extensions, garages, porches, balconies and dormers. It needs dry conditions and a proper substrate to be installed correctly, which matters in Irish weather planning. See GRP fibreglass roofing.

EPDM rubber roofing

EPDM is a synthetic rubber membrane, usually bonded to the deck and often installed as a single sheet on domestic-sized roofs, which means very few joints. It is flexible and accommodates movement well.

It suits straightforward rectangular roofs particularly well, and is more awkward where there are many penetrations and complicated upstands, since every one of those has to be detailed individually. See EPDM roofing.

Liquid roofing systems

Liquid systems are applied cold, usually with a reinforcing fleece, and cure to form a seamless membrane that follows whatever shape it is applied over.

Their strength is detailing: awkward upstands, pipe penetrations, plant bases, balconies and refurbishment over existing coverings where conditions allow. They depend heavily on substrate preparation and correct application thickness. See liquid roofing.

What actually decides the right system

Considerations

• Shape and size of the roof, and how regular it is
• Number of penetrations, upstands, kerbs and abutments
• Deck type and condition — this frequently decides everything else
• Drainage: falls, outlet positions and whether water currently ponds
• How the roof is used: purely weatherproofing, foot traffic, a balcony, a terrace
• Whether it is visible from windows above, which makes appearance relevant
• Access for installation and for future maintenance
• Existing build-up and whether it can be overlaid or has to be stripped

Repairability and maintenance

All four systems can be repaired, and none of them are maintenance-free. Outlets and gutters need to be kept clear, debris should not be allowed to sit, and details should be looked at periodically.

Where a flat roof fails early, the cause is usually the same regardless of system: poor falls, an inadequate outlet, a badly formed upstand, or a covering laid over a deck that was already wet.

Choosing without being sold to

There is no universal winner among these systems, and we would be sceptical of anyone who tells you otherwise. What we do is look at the roof, the deck, the drainage and the detailing, then set out which systems are genuinely suitable and why.

Related: flat roofing, felt vs fibreglass and the flat roof cost guide.