If you have a leaking fibreglass roof in Sussex, you are definitely not the only one. I have looked at many of these roofs around Brighton, Hove, Worthing and nearby areas, and the pattern is often very similar: the roof looked clean and solid when it was first installed, but later the leak appeared around a wall, edge trim, outlet, corner, or a small crack that did not look serious at first.
I do not install GRP trim and edge-detail systems myself, so I am not writing this as an installer trying to defend the material. I usually see these roofs when something has already gone wrong. From that side of the work, my view is simple: this type of covering can be very unforgiving on roofs that move, hold water, or have complicated details. If you are already looking at options for repairing a leaking GRP covering, the first step should always be diagnosis rather than simply adding another coat. I am also cautious when I see standing water around a GRP surface, because ponding can make small defects show up much faster.
You Are Not the Only Homeowner With This Problem
One thing I would say straight away is this: a leaking fibreglass roof does not automatically mean you did something wrong as a homeowner. I often meet people who feel embarrassed because they chose fibreglass after being told it was strong, modern and long-lasting. In many cases, the material looked sensible at the time.
The difficulty is that a roof is not a fixed piece of furniture. It is exposed to rain, wind, cold nights, hot sun, moisture in the building, and normal movement in the structure below. Across Sussex, that movement is made worse by coastal weather, wind-driven rain and older building details. A roof that performs reasonably in a simple situation can struggle badly once parapet walls, poor falls, old timber decking, or several edge details are involved.
Why Fibreglass Roofs Often Leak in Similar Places
When I inspect a leaking fibreglass roof, I rarely find that the whole surface has suddenly failed in one dramatic way. More often, the leak starts at a stress point. The surface may still look hard and clean, but a small defect is allowing water into the roof build-up.
The repeat leak points I see are usually:
- edge trims where wind and water work under weak detailing;
- wall junctions where the fibreglass meets brickwork, render or lead flashing;
- internal corners where movement is concentrated;
- outlets and drainage points where water sits after rain;
- board joints where the deck below has moved;
- old repair patches where another layer has been added over the same problem.
These are not unusual defects. They are the normal places where a hard waterproof surface gets tested on a real roof.
The Problem With a Roof That Cannot Move Enough
Fibreglass feels strong because it is hard. That is also one of the reasons it can fail on certain roofs. A flat or low-pitched roof needs to cope with substrate movement. The boards below can expand and shrink. Timber joists can flex. A wall junction can move differently from the roof deck. If the waterproofing layer cannot tolerate that movement, the stress eventually shows somewhere.
That is why some fibreglass leaks appear as tiny hairline cracks rather than a large hole. Water only needs a very small route in. Once it gets beneath the surface, capillary action can pull moisture sideways through narrow gaps, so the damp patch indoors may appear away from the visible defect outside.
This is one reason I am cautious with fibreglass on larger or more complicated roofs. A small simple entrance roof may have fewer movement problems. A larger roof with several details, upstands and changes of direction is a much harder test.
Sussex Weather Makes Weak Details Show Up
Brighton, Hove and Worthing roofs deal with plenty of wind-driven rain. On exposed properties, rain does not always fall neatly from above. It can be pushed sideways against trims, upstands, parapet walls and flashing details. If the fibreglass finish has a tiny crack or weak edge, water may find it faster than the homeowner expects.
Older Sussex properties also add another layer of difficulty. Victorian and Edwardian buildings often have ageing brickwork, parapet walls, old render, mixed roof levels and timber structures that have moved over many years. A rigid roof covering has to meet all those imperfect details. If the preparation or detailing is not excellent, the weak point usually appears later as a leak.
Why the Leak May Have Been There Before You Saw It
A leaking roof does not always show itself immediately on the ceiling. This is especially true with low-slope roofs. Water may soak into insulation, sit in the deck, run along timber, or track into a wall before it finally appears indoors.
I have seen roofs where the homeowner only noticed the problem after a stain appeared, but the roof had clearly been holding moisture for much longer. Sometimes the ceiling looks fine because the water is travelling into masonry or insulation instead of dripping straight through. That hidden moisture can still damage the roof build-up.
This is why I take damp smells, soft areas, bubbling, stains around the fascia, or repeated mould seriously. They may be telling us the roof has been wet for some time, even if there has not been active dripping inside the room.
Common Misunderstandings About Leaking Fibreglass Roofs
“It only needs another coat.”
Sometimes a coating or local repair can help, but only when the roof is dry, stable and the defect is genuinely local. If the roof is moving, holding water, or wet underneath, another coat may only hide the problem for a short time.
“The crack is tiny, so it cannot be serious.”
A tiny crack can still be enough for water ingress. On a low-slope roof, water can sit over the same small crack repeatedly. The size of the visible crack does not always match the amount of moisture travelling below the surface.
“There is no ceiling stain, so the roof is not leaking.”
Water can move into insulation, timber or walls before showing indoors. A roof can be leaking without an obvious internal stain straight away.
“Fibreglass is strong, so it should not fail.”
Strength is not the only issue. A roof covering also needs flexibility, proper detailing and a sound deck below it. A hard material can still crack if the structure below moves.
When the Roof May Still Be Repairable
I would not automatically say every leaking fibreglass roof needs replacing. That would not be fair. Some roofs can be repaired if the problem is small, local and caught early enough.
A repair may be realistic if:
- there is one clear defect rather than cracks in several places;
- the surrounding fibreglass is still firmly bonded;
- the deck below feels solid and dry;
- there is no serious ponding water over the defect;
- the leak is not coming from a complicated wall or parapet detail;
- there are no repeated failed patches in the same area.
Even then, the preparation has to be right. A repair over damp, dirty, loose or unstable material is unlikely to last. The roof must be assessed properly before money is spent on the surface.
When I Become More Concerned
I become more cautious when the roof shows signs of a wider failure. These are the situations where a small patch may not be honest advice:
- cracking around several edges or corners;
- ponding water sitting after rain;
- bubbling or hollow areas in the fibreglass;
- soft or springy roof decking;
- stains near parapet walls or upstands;
- water marks around fascia or soffit areas;
- several old repairs that have failed again;
- leaks that return after every spell of heavy rain.
In those cases, the roof may need more than a surface repair. The deck, falls, drainage, trims and wall details all need checking. If the structure underneath has been wet for a long time, the covering is only one part of the problem.
Why I Often Compare Fibreglass With SBS Felt
When a fibreglass roof is badly failed, I often discuss replacement with a more practical low-slope roofing system, especially SBS torch-on felt. I frequently use Tecnatorch SBS Torch-On Mineral Felt Charcoal because it is a repairable, flexible and proven material when installed over a sound deck.
The main difference from my point of view is long-term maintainability. Fibreglass can become awkward once it has cracked, lifted, trapped moisture or been patched several times. A properly installed SBS torch-on felt build-up is usually easier to detail, repair and renew later, provided the deck below remains structurally sound.
That does not mean felt is magic. Poor workmanship can ruin any roofing system. But on many domestic roofs with awkward details, I prefer a material that gives the homeowner more realistic repair options years later.
Do Not Ignore Walls and Flashing
Not every leaking fibreglass roof is leaking only through the fibreglass. Around Sussex, I often have to check brickwork, render, lead flashing, parapet walls and coping stones. Water can come through a wall and appear to be a roof leak. It can also get behind a weak upstand and travel under the roof surface.
If your roof meets a parapet or party wall, the wall detail deserves proper attention. In some cases, waterproofing for parapet walls is just as important as the roof covering itself.
If you want a more detailed breakdown of the causes, I have also written about common causes of GRP leaks on low-slope roofs.
What I Would Do Before Agreeing to a Repair
Before choosing any repair method, I would want to know what the roof is actually asking for. That means checking more than the visible crack.
My usual approach is:
- look at the internal damp pattern and when it appears;
- inspect the roof surface for cracks, bubbles and old repairs;
- check whether water is ponding after rain;
- inspect trims, edges, outlets and upstands;
- look carefully at brickwork, render and lead flashing;
- assess whether the deck may be soft or moisture damaged;
- decide whether repair, temporary weatherproofing or replacement is the fair recommendation.
That order matters. A repair should follow the diagnosis, not replace it.
My Honest View
If your fibreglass roof is leaking, you are not alone. I have seen this problem many times across Sussex, and it does not always mean the homeowner was careless or unlucky. Often, the roof has simply reached the point where movement, water and weak details have exposed the limits of the system.
A small local repair may be fair when the roof is mostly sound. But if the fibreglass has cracked in several places, the deck is wet, the trims are failing, or water keeps sitting on the surface, I would be careful about spending money on another short-term patch.
The best next step is to find the real route of moisture ingress before deciding what to do. Sometimes that leads to a sensible repair. Sometimes it shows that replacement is the more honest answer. Either way, the roof should be judged by its actual condition, not by what the material looked like when it was first installed.