Signs Your Flat Roof Needs Replacing (Not Just Repairing) 12th November 2025
Published by the team at Avant Garde Roofing Solutions
Over 20 years of flat roof installations across the Midlands
Let's start with the simplest factor – how old is your roof?
If your flat roof is made from traditional felt and it's over 15 years old, you're living on borrowed time. We've seen felt roofs last 20+ years when they've been exceptionally well maintained, but that's the exception rather than the rule. Most felt roofs start showing serious problems after about 12-15 years.
Other materials have different lifespans:
- Traditional felt: 10-15 years (sometimes up to 20 with excellent maintenance)
- Modified bitumen: 15-20 years
- EPDM rubber: 25-30 years
- Fibreglass (GRP): 30+ years
- Single ply membrane: 25-35 years
We replaced a felt roof in Bedford last month that was original to the 1995 extension. The owner had been patching it every couple of years for the last decade. When we finally stripped it off, the decking underneath was so water-damaged that we had to replace half of it. If they'd replaced the roof five years earlier, they'd have saved the cost of all those repairs plus the decking replacement.
Widespread Cracking and Splitting
One visible crack or split section could easily be repaired, particularly if it is addressed early on, however, if you can see cracks scattered all over the roof surface, that is an entirely different issue.
This scenario is mostly because the roofing material has aged and the continuous exposure to the UV rays and the fluctuating temperatures weather conditions has over time deteriorated the roofing material. Once this deteriorating process has started, it just turns to an avalanche—one crack becomes two, two becomes five, and in no time you are looking at a roof that looks like a dried up riverbed.
This is especially the case with older felt roofs. The felt becomes inflexible, and struggles to cope with the changes in temperatures. For this reason, one new crack becomes a continuous chain and if you are trying to cover it with a ‘patch’, it is pointless.
Check For:
- Multiple cracks across different areas of the roof
- Widening cracks over time
- Brittle or crispy material upon touch
- Splits along seams or joins
Visible Deterioration of the Roof Surface
Sometimes you can literally see that a roof has had it. Get a ladder up (safely, or better yet, get a professional to look) and check the roof surface.
Blisters and bubbles: There is the ability to repair small blisters, however, if the entire roof is covered in bubble wrap, then moisture has breached the membrane, and is the worst case scenario. This is an indication of an adhesive bond failure, or water penetrating the layers. Once this occurs over an expansive surface area, effective repair becomes impossible.
Visible yet exposed: If the mineral surface is completely missing, or if the base layer is visible, then ultra violet rays are causing damage and destruction to the roof. This is extremely detrimental, and in some cases, terminal to the felt roof.
Slits and gaps: One or two gaps can be repaired, however, if more than two, then the material is in a state of weakness, and extreme brittleness.
Edges: If the roof covering is peeling back or along places like vents, it has lost adhesion. This becomes worse over time and allows water to penetrate the roofing system.
Not too long ago, an owner was sure all their roof required was a little glue. Based on the owners statement, we gathered that the material was completely lost, and it was in the worse state of devastation, where no more physical support was possible. This was evident in the Luton garage where the roof was able to, with almost no energy, all the felt was able to be lifted with little to no energy.
Excessive moss and vegetation growth
It’s normal to find moss in gutters occasionally. However, if moss is sprawling across the vast surface area of your roof, it’s rather alarming.
Moss growth suggests stagnant water, roof surface deterioration, and moisture being trapped within roofing materials. We’ve even observed tiny plants sprouting in debris-filled crevices.
If the roof is partially covered in moss and the roofing material is in good condition, it’s possible to extend the roof’s lifespan by cleaning and treating it. Otherwise, if the roof retains water, porous and water-retentive, the situation is purely cosmetic and the underlying problem persists.
Water Between the Layers (Interstitial Moisture)
This is harder to spot without taking samples, but it's a common problem with older felt roofs and poorly installed systems.
If water gets between the layers of a built-up felt roof, it can travel around underneath the top layer. This means you might get leaks appearing in places far from where the water is actually getting in. It also means the layers are delaminating, and the roof is failing from the inside out.
Signs of interstitial moisture include:
- Leaks that move around or appear in unexpected places
- Soft or spongy areas when you walk on the roof
- Bubbling that covers large areas
- A squelching sound when you put pressure on certain spots
There's no effective repair for this. Once water is travelling between the layers, you need to strip it all off and start again.
Your Insulation Needs Upgrading Anyway
Building regulations have changed significantly over the years, and if your flat roof is more than 15-20 years old, its insulation probably doesn't meet current standards.
If you're going to be doing major work on your flat roof, Building Control will likely require you to upgrade the insulation to meet current U-values. This often means you can't just patch or overlay the existing roof – you need to strip it back to the structure and rebuild it with proper insulation.
This is particularly relevant if you're planning to sell your property or if you've had a survey that's flagged poor insulation. Rather than doing a temporary repair now and then having to upgrade later, it makes sense to do a complete replacement with modern insulation standards.
The "Overlay" Has Already Been Done
Some roofing companies offer to install a new roof covering over the existing one rather than stripping it off. This can work as a medium-term solution, but it has limitations.
If your roof has already been overlaid once, you generally can't do it again. The structure isn't designed to support multiple layers of roofing material, and each layer traps moisture and problems underneath. If you've already got two layers and you're having problems, stripping back to the deck is your only option.
We see this quite often with garages and extensions where someone has tried to avoid the cost of a full replacement. It buys you 5-10 years at best, but when problems start appearing, you've run out of shortcuts.
How We Make the Call: Repair or Replace?
When we survey a flat roof, we're looking at all these factors together, not just one or two issues in isolation. We've developed what we call the "one-third rule" over the years:
If repairs would cost more than one-third of a replacement, replacement makes better financial sense.
Why? Because repairs on a deteriorating roof rarely last as long as repairs on a relatively new roof. You might get two years from a repair that cost £800, but a £4,000 replacement would last 25+ years. The maths isn't even close.
We also consider what's happening underneath. If the decking is sound and dry, repairs are more viable. If there's water damage to the structure, you're going to need major work anyway, so you might as well do it properly.
The Cost Question Everyone Asks
"How much does a flat roof replacement cost?" is usually the first question after "do I really need to replace it?"
The honest answer is: it depends on size, access, what we find when we strip the old roof off, and what system you choose. But here are ballpark figures for the Midlands area:
- Small domestic garage (3m x 6m): £2,500-£4,000
- Large garage or medium extension: £4,000-£6,500
- Large extension or small commercial unit: £6,500-£12,000
- Substantial commercial roof: £12,000+
These prices assume:
- Standard access with scaffolding if needed
- Sound decking that doesn't need replacing
- Modern system (EPDM or fibreglass) with proper insulation
- Replacement of flashings and trim work
Yes, it's a chunk of money. But compare that to spending £500-£800 every year or two on repairs that don't last. Over a 10-year period, repeated repairs can cost more than a replacement, and you'll still need the replacement at the end.
What About Insurance?
This comes up a lot. Will insurance cover your flat roof replacement?
Generally, no – insurance covers sudden damage from things like storms or fires, not gradual deterioration or wear and tear. If a tree falls on your roof, insurance might pay for the damage. If your roof has simply reached the end of its natural life, that's maintenance, not an insured event.
However, if a failing roof has caused water damage to your property, your insurance might cover the internal damage even if they won't pay for the roof itself. It varies by policy, so check your documents or speak to your insurer.
Making the Decision
Look, we're not here to oversell you on a replacement if repairs will genuinely do the job. We've turned down work before when a customer was convinced they needed a new roof but actually just needed some flashing repairs and a good clean.
But we're also not going to take your money for repairs that we know won't last. If we tell you your roof needs replacing, it's because we've seen enough of them to know when one's reached the end of the road.
Here's our advice process:
If your roof is showing one or two of the issues from this list, and it's not particularly old, repairs might be a sensible option. Get a proper survey done, get the repairs specified clearly, and ask for realistic expectations about how long they'll last.
If your roof is showing multiple issues, especially if it's over 15 years old for felt or 25 years for other materials, replacement is probably the smart money. Factor in the cost of repairs you've already done, the cost of ongoing maintenance, and the hassle of dealing with leaks, and suddenly the replacement doesn't look quite so expensive.
Get multiple opinions, but make sure they're qualified opinions. A proper roofer will give you options and honest advice about what makes financial sense. Anyone who immediately jumps to "you need a complete replacement" without explaining why, or conversely, anyone who promises repairs will solve deep-seated structural problems, should ring alarm bells.
What Happens If You Ignore It?
We've had customers who've delayed replacing an obviously failing roof for years, hoping it'll somehow last just a bit longer. It never does, and the bill when they finally have to do something about it is always higher than it would have been earlier.
Here's what we've seen happen:
- Water damage spreads to the ceiling joists and internal walls
- Mould growth creates health issues
- Electrical fittings get water-damaged (expensive and dangerous)
- Insulation becomes waterlogged and useless
- The timber structure rots and needs replacing
- Insurance companies refuse to cover water damage if they think the roof hasn't been maintained
Delaying an inevitable replacement doesn't save money – it just means you're paying for water damage on top of the roofing work.
Our Replacement Process
When you do commit to a replacement, here's what you can expect from us:
- Proper survey: We'll look at the whole roof, check the structure underneath, and give you a written quote with a breakdown of what's included.
- Clear timeline: We'll tell you how long it'll take and when we can start. Most domestic roofs take 2-5 days depending on size and complexity.
- Our own team: We don't use subcontractors. The same team that surveys your roof will be the ones installing it.
- Weather protection: Your roof won't be left open overnight. We'll make sure you're watertight at the end of each day.
- Proper guarantees: 20, 25, or 30-year guarantees depending on which system you choose, insurance-backed where applicable.
The Bottom Line
After 20+ years of working on flat roofs, we can usually tell within five minutes whether a roof is repairable or needs replacing. The signs are pretty clear once you know what to look for.
A survey might confirm your worst fears that replacement is needed, but at least you'll know for certain and can plan accordingly. Or it might reveal that targeted repairs will give you several more years of service. Either way, you'll have the information you need to make the right decision.
What you shouldn't do is keep throwing money at temporary fixes while hoping the problem will go away. Flat roofs don't heal themselves, and hoping for the best is an expensive strategy.
Concerned about your flat roof? We offer free, no-obligation surveys across Northamptonshire, Bedfordshire, Buckinghamshire, Leicestershire, Oxfordshire and Warwickshire. Give us a call on 0800 456 1104 and we'll give you honest advice about what your roof actually needs – not what makes us the most profit.
About Avant Garde Roofing Solutions: We've been installing and repairing flat roofs across the Midlands since 2003. After more than 2,000 installations, we've learned to spot the difference between a roof that needs repairing and one that needs replacing. We're Which? Trusted Traders and part of the Buy with Confidence scheme, which means we're committed to honest advice and quality work.