Common GRP Fibreglass Roofing Problems and How to Fix Them

GRP fibreglass is one of the most durable flat roofing systems available, but it's not completely problem-free. Understanding what can go wrong helps you spot issues early and avoid expensive repairs.

Crazing and Surface Cracking

The most common issue with GRP roofs is crazing — fine surface cracks in the topcoat. This is usually a surface cosmetic issue caused by UV exposure and doesn't necessarily indicate water ingress. However, deep cracks that penetrate into the laminate need attention.

Star Cracking

Star or stress cracks radiate from a central point and are usually caused by impact (someone dropping something heavy) or by structural movement in the decking below. These should be investigated and repaired promptly.

Delamination

Delamination — where the GRP laminate separates from the deck — can occur if the roof was installed over a damp deck, or if water has penetrated through a crack and then frozen. Delaminated areas feel soft or springy underfoot.

Failed Joints at Trims

The junction between the GRP membrane and the drip trim or upstand trim is a common failure point if the original detailing wasn't done correctly. Water can run behind the trim and cause leaks at the fascia line.

Getting Repairs Right

GRP repairs must use compatible materials — the same resin system as the original installation. Applying incompatible products (especially bitumen-based products) can prevent future repairs and may delaminate the existing laminate. Always use a specialist GRP roofer.