How to install fibreglass flat roofing on a garage

Installing a fibreglass flat roof on your garage can be a durable and cost-effective solution that provides a long-lasting, weather-resistant covering. With the right tools and materials, and by following a detailed guide, you can achieve a professional-quality installation. Here’s a comprehensive step-by-step guide to help you through the process.

Materials and Tools Needed

Before starting, gather all necessary materials and tools:


  • Fibreglass roofing resin
  • Fibreglass matting
  • Top coat resin
  • Trims and edging
  • Roof decking boards
  • Roofing adhesive
  • Fixings (nails, screws)
  • Acetone (for cleaning)
  • Protective clothing and gear


  • Measuring tape
  • Saw
  • Drill
  • Roller brushes
  • Paint brushes
  • Scissors or utility knife
  • Hammer
  • Sanding tools

Step 1: Prepare the Roof Surface

1.1. Remove Old Roofing Material Start by removing any old roofing material from the garage roof. Ensure the surface is clean and free of debris. If there are any damaged areas on the decking, replace them with new boards.

1.2. Inspect and Repair the Decking Inspect the roof decking for any signs of damage or rot. Replace any damaged sections to ensure a solid foundation for the fibreglass. Make sure the decking is dry before proceeding.

Step 2: Install Roof Trims and Edge Details

2.1. Fix Drip Trims Install the drip trims around the edges of the roof to ensure water runs off correctly. Secure them with nails or screws, ensuring they are firmly in place.

2.2. Install Edge Trims Edge trims provide a neat finish and help to secure the fibreglass matting. Attach these along the roof edges, making sure they are flush with the surface of the decking.

Step 3: Apply the Fibreglass Matting

3.1. Cut the Fibreglass Matting Measure and cut the fibreglass matting to fit the roof surface. It’s essential to have pieces that will overlap slightly to ensure complete coverage.

3.2. Mix the Roofing Resin In a clean container, mix the fibreglass roofing resin according to the manufacturer’s instructions. The resin will harden over time, so only mix what you can use within a short period.

3.3. Apply the Resin Using a roller brush, apply a layer of resin onto the roof decking. Work in manageable sections to ensure the resin doesn’t begin to harden before you can lay the matting.

3.4. Lay the Fibreglass Matting Carefully place the fibreglass matting onto the wet resin. Use a roller brush to press the matting into the resin, ensuring there are no air bubbles or wrinkles. Repeat this process, overlapping the edges of each piece of matting.

3.5. Apply Additional Resin Layers Once the matting is in place, apply another layer of resin over the top. Use a paintbrush for detailed areas and a roller brush for larger sections. Allow this layer to cure according to the manufacturer’s recommendations.

Step 4: Apply the Top Coat

4.1. Prepare the Top Coat Resin Mix the top coat resin in a clean container, following the instructions provided. This layer provides UV protection and a smooth finish.

4.2. Apply the Top Coat Using a clean roller brush, apply the top coat evenly over the entire surface of the roof. Make sure to cover all areas thoroughly to protect the fibreglass matting underneath.

4.3. Allow to Cure Allow the top coat to cure completely. This process can take several hours to a full day, depending on the environmental conditions and the specific product used.

Step 5: Finishing Touches

5.1. Clean Up Clean all tools and equipment with acetone before the resin hardens. Dispose of any waste materials according to local regulations.

5.2. Inspect the Roof After the top coat has fully cured, inspect the roof for any missed spots or imperfections. Touch up any areas as needed to ensure a uniform and watertight finish.

5.3. Install Final Trim Pieces If necessary, install any final trim pieces to complete the roof. This may include additional edge trims or flashings to ensure a neat and professional look.

Maintenance Tips

To ensure the longevity of your new fibreglass flat roof, follow these maintenance tips:

Regular Inspections: Perform regular inspections, especially after severe weather. Look for signs of damage or wear, such as cracks or blisters.

Clean the Surface: Keep the roof surface clean and free of debris. Leaves and dirt can trap moisture, leading to potential issues.

Address Repairs Promptly: If you notice any damage, address it promptly to prevent further deterioration. Small cracks or blisters can be repaired with additional resin and matting.

Check for Ponding Water: Ensure the roof has adequate drainage and there are no areas where water can pool. Ponding water can lead to premature deterioration.


Installing a fibreglass flat roof on your garage is a project that requires careful preparation and attention to detail. By following these steps, you can achieve a durable, weather-resistant roof that will protect your garage for years to come. Always refer to the manufacturer’s instructions for specific products and materials used, and don’t hesitate to consult a professional if you encounter any challenges. With the right approach, you can enjoy the benefits of a high-quality fibreglass flat roof.

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