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Fiberglass roofs are popular options for flat roofs on both residential and commercial properties for many reasons. We created this guide to give property owners a better idea of what glass reinforced polyester (GRP) roofs and why a GRP roof might be your best option for your property. 

What is a Fiberglass Roof?

A fiberglass roof is a composite material formed by combining polyester and fine strands of fiberglass to form a laminate. Layers of fiberglass mats are wetted out and then once cured, coated with a topcoat. Fiberglass roofs have no seams, joints, or welds so water will not pool or leak, making them almost completely waterproof. 

Fiberglass roofs are designed to last 25 to 30 years without any signs of deterioration if installed correctly. 

How is a Fiberglass Roof Installed?

Weather is very important when installing a fiberglass roof since it is laid as a liquid. Dry, mild weather conditions are needed. Fiberglass roof installations require lots of preparation and experience. It’s recommended to have a professional roofer come to install your new fiberglass roof, but here’s a basic idea of how the installation of a fiberglass roof goes:

  1. Removal of existing roofing felt or substance to expose joints
  2. 3/4in plywood is laid on the roof to provide a base for the resin to adhere to
  3. Fiberglass roof drip trims are installed on all of the edges of the roof to direct water runoff to gutters
  4. Seams are covered with a waterproof matting
  5. GRP is laid out
  6. Topcoat is installed to secure the fiberglass and give the tack-free layer

Advantages of a Fiberglass Roof

Fiberglass Roof Maintenance

To keep that new look for your roof, then a little cleaning will have to be done every once in a while with a mop or brush to clean off dirt and debris. Avoid using a pressure washer with hot steam because that can damage the topcoat of the roof. 

Over time you may start to see small cracks or GRP pinholes where the top layer has started to wear away. This is often due to poor installation, if the temperature is not right, or if the resin mixture was not the correct ratio. Another sign of wear is if water is pooling on the roof. A new coat will smooth the roof out and weatherproof it again. 

There are two options for coating a deteriorating fiberglass roof. Those are a gel coating or acrylic paint. The gel coat is sprayed on and sanded down once cured. Acrylic paint is applied with a rolling brush over a latex primer. Both options will make the roof look as good as new but should be installed by a professional to ensure it is installed correctly. 


A fiberglass roof is a durable, waterproof roofing option for both residential and commercial properties. Fiberglass roofs are made out of glass-reinforced polyester that is installed by combining fiberglass sheets and a polyester resin. Fiberglass roofs need minimal maintenance aside from the occasional brush or mop with water.

If a fiberglass roof is showing signs of wear with cracks and pinholes, then a coating of acrylic or a gel coating can be applied to get the roof back to new. If you are thinking about having a fiberglass roof installed or need a gel or acrylic coating, then you should contact the roofing experts at Philly’s Phinest Roofing for a free estimate.