Why The System Matters
A flat roof is not truly flat. It needs a slight fall so that water drains away, and the covering must be fully watertight with careful detailing at edges, upstands and penetrations. Most flat roof failures start at the details, not in the middle of the roof, which is why the installation matters as much as the system.
All three of the common systems can perform well when fitted properly. The differences are in how they are installed, how they cope with awkward shapes, and how they suit your budget.
The Three Main Systems
A quick guide to each:
Torch-on felt
Layers of reinforced bitumen felt are heat-bonded to the roof. A proven, cost-effective and widely used system, particularly for straightforward roof shapes.
Cold applied liquid
A liquid membrane is applied to the roof and cures into a seamless, fully bonded covering. Well suited to awkward shapes, detailing and repairs, with no joins to open up.
EPDM rubber
A single-ply rubber membrane known for its flexibility, weather resistance and long service life. Often chosen where a clean, large, uninterrupted surface is wanted.
Side By Side
General guidance only. Your roof, access and budget will shape the best choice.
| Torch-on felt | Cold applied liquid | EPDM rubber | |
|---|---|---|---|
| Type | Multi-layer bitumen felt, heat-bonded | Seamless liquid-applied membrane | Single-ply rubber sheet |
| Good for | Simple roof shapes where value matters | Awkward shapes, many details, and repairs over existing roofs | Larger, cleaner roof areas and long service life |
| Joins | Overlaps sealed by heat | None, it is seamless | Few, with large sheets and bonded seams |
| Installation | Uses a flame, so careful site safety is essential | Applied by roller or brush, no flame needed | Bonded to the deck in large sheets |
| Consider | Edge and upstand detailing | Weather during application and curing | Correct bonding and edge trim detail |
Repair Or Replace?
A small leak does not always mean replacing the whole roof. Localised damage, a failed joint or a worn flashing can often be repaired, and some liquid systems can be applied over a sound existing roof. A roof with widespread blistering, repeated leaks, ponding water or a soft deck is more likely to need replacing.
The deck underneath matters too. If it has been wet for a long time, it may need repairing before any new covering goes on.
What To Look For In A Flat Roof Quote
To compare quotes fairly, check that each one makes clear:
- Which system is being used and why
- What happens to the existing covering and deck
- How edges, upstands and outlets will be dealt with
- What the fall and drainage arrangements are
- What guarantee comes with the work
Free “Is My Roof Failing?” Checklist
A one-page checklist you can use from the ground and the loft to spot the early warning signs. Free to download.
Get The Free ChecklistThe Bottom Line
Felt, liquid and EPDM can all make a good flat roof. The best choice depends on the shape of the roof, access, the condition of the deck and your budget, and the quality of the installation counts for as much as the material.
Frequently Asked Questions
Which flat roof system is best?
There is no single best system. Torch-on felt is a proven, cost-effective choice, liquid suits awkward shapes and details, and EPDM is known for flexibility and a long service life. An inspection is the best way to pick the right one for your roof.
How long does a flat roof last?
It depends on the system, the quality of installation and how well the roof is maintained. See our guide on how long roofs last for more detail. A proper inspection will tell you where your own roof stands.
Can a flat roof be repaired rather than replaced?
Often, yes. Localised damage, failed joints or worn flashings can frequently be repaired. Widespread blistering, repeated leaks or a damaged deck is more likely to need replacement.
Why does my flat roof keep ponding water?
Standing water usually means the fall is poor or the deck has dipped. Over time it can shorten the life of the covering, so it is worth having it checked.
Is torch-on felt safe?
Torch-on felt is installed using a flame, so it should only be carried out by an experienced, insured installer who follows proper safety practice. We are fully insured and take site safety seriously.
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