Are flat roofs really a bad thing to have?

20 August 2026 · 6 min read

Tell someone the house has a flat roof and you can watch them wince. Flat roofs have worried buyers for decades, and some of that worry was earned. But the flat roof you'd get today can be a very different thing from the one that gave the whole category its name, and the covering matters far more than the shape.

Why flat roofs got their reputation

Most of the bad stories trace back to thin, old-style felt roofs laid over weak decks with poor detailing at the edges and upstands. Add standing water and a few winters, and leaks followed. A roof that isn't properly built will fail whatever it's covered with, and that's worth remembering when you read the rest of this.

Torch-on felt: fine, but no longer the best

Modern high-performance torch-on felt, laid in two or three layers with a cap sheet, is a long way from the single-layer felt of the past, and a good one can give 15 to 25 years. It's still a sound, affordable choice. But it's applied with a naked flame, which means fire risk and careful hot-works precautions, and today there are coverings that last considerably longer with no flame on the roof at all.

GRP fibreglass: a note of caution

GRP is popular, and done well it can give 20 to 30 years. My hesitation is that it's a rigid, hard-setting material sitting on a building that moves. Timber decks flex, and UK weather swings from freezing to hot sun. Where the deck isn't perfectly stable, or the laminate is thin, GRP can crack or split, usually at joints and upstands. It also needs a dry deck and suitable temperatures to lay properly. That doesn't make it a bad roof, but it does mean the quality of the deck and the installer matter more than the brochure suggests.

EPDM rubber, including Resitrix

EPDM is a synthetic rubber that stays flexible across a wide temperature range, which is what a flat roof needs. It's now the most popular domestic flat roof covering in the UK, and the long-life end of the market is excellent.

Resitrix is a good example. It's a slim, single-layer membrane with an EPDM surface over a reinforced bitumen backing. The manufacturer says it is UV-resistant without any extra surface protection, and the self-adhesive version is slip-resistant and suitable for foot traffic, so it works for walkways and small terraces. The joints are welded with hot air, so there's no naked flame. Suppliers quote a life expectancy of up to 50 years, with a 20-year guarantee when installed by trained installers. Those are manufacturer figures rather than promises, but they're a long way beyond felt.

I hold a Resitrix installer certification, which is why I can talk about how it should be laid. I don't fit or sell it now, and I'm not tied to any manufacturer, so it's one option in this list rather than a recommendation to buy.

Liquid-applied systems: Elastathane

Liquid systems are brushed or rolled on and cure into a seamless membrane. Elastathane is a cold-applied polyurethane product of this kind. The main advantage is that there are no joints to fail and no flame, so it suits awkward roofs with lots of pipes, upstands and corners, and it can often be applied over an existing roof that's still sound, avoiding a full strip-off. Typical lifespans are around 20 to 25 years. It's worth checking that any specific product is still current and covered by a manufacturer's guarantee before you commit, because product lines change.

What do they cost?

These are typical 2026 supply-and-fit ranges per square metre from UK trade pricing guides. Real quotes vary widely with roof size, access, insulation and location, so treat them as a rough guide only.

• Torch-on felt: roughly £50 to £100 per m², with a 15 to 25 year life.
• GRP fibreglass: roughly £90 to £140 per m², with a 20 to 30 year life.
• EPDM rubber: roughly £80 to £120 per m², with 30 to 50 years quoted. Premium systems sit towards the upper end.
• Liquid systems: roughly £60 to £100 per m², with a 20 to 25 year life.

Insulation, stripping off the old covering, scaffolding and any rotten decking are extras, and deck condition is the biggest source of surprises. A covering that costs a little more but lasts twice as long is often the cheaper option over time.

Preparation matters more than the product

• Felt: a sound, dry deck, proper falls, and fire precautions for the hot works.
• GRP: a rigid, well-fixed, dry deck (usually new boards), correct trims, and dry weather with suitable temperatures.
• EPDM and Resitrix: a clean, dry, smooth, sound deck, a primer for the self-adhesive types, and careful detailing at edges and upstands. Damaged decking is replaced first.
• Liquid: a thoroughly cleaned, repaired and primed surface, with reinforcement at details. Existing felt must be sound enough to go over.

In every case, the roof needs some fall so water runs off. Standing water speeds up wear on any covering.

So, is a flat roof a bad thing to have?

No, not if it's built properly. With the right covering, a sound deck and good detailing, a flat roof can give decades of service and hold its own against the main pitched roof. If you're buying a house with one, the things to find out are what it's covered with, how old it is and how long it's got left. That's exactly what a roof inspection will tell you.