How to Waterproof a Garage Roof with EPDM

Waterproofing a garage roof with EPDM (Ethylene Propylene Diene Monomer) is a popular and effective method, particularly for flat or low-pitched roofs. EPDM is durable, flexible, and resistant to UV rays, making it an ideal choice for waterproofing.

Fast and easy to install, a small, skilled DIY team can easily waterproof a garage roof with EPDM. We’re here to help, with a step-by-step guide.

How to install an EPDM membrane on a garage roof

Step 1. Assess and prepare the roof

• Inspect the roof: Check the roof for any damage, such as cracks, holes, or weak spots. Repair these areas before installing the EPDM membrane.
• Clean the roof: Remove dirt, debris, old roofing material, and loose particles from the roof surface. A clean, smooth surface is crucial for proper adhesion.
• Ensure dryness: Make sure the roof is completely dry before applying the membrane, as moisture can affect adhesion and the waterproofing effectiveness.

Step 2. Measure and cut the EPDM membrane

• Measure the roof area: Measure the dimensions of the roof to determine the size of the EPDM membrane you need. Ideally, use a single sheet to cover the entire roof. RubberCover EPDM is best for this, as it can be cut to any size up to 15m x 60m – waterproofing a garage roof with EPDM is faster and more reliable with no seams. Buy a standard garage roof kit or a custom-cut flat roof kit to simplify quantities,
• Cut the EPDM sheet: If using multiple pieces, cut the EPDM membrane slightly larger than the roof dimensions to allow for overlap at the edges and seams (typically 100-300 mm of overhang).

Step 3. Apply the primer (if required)

• Primer application: Some EPDM systems require a primer for better adhesion, especially on certain surfaces like concrete. Apply the primer evenly across the roof surface and let it dry as per the manufacturer’s instructions.

Step 4. Position the EPDM membrane

• Lay out the membrane: Unroll the EPDM membrane and position it over the garage roof. Allow it to relax for 30 minutes to an hour to avoid any tension that could lead to wrinkles.
• Align the membrane: Ensure the membrane is centred and covers the roof fully, with overhangs for trimming and overlap at edges.

Step 5. Apply the adhesive

• Use the correct adhesive: Use a water-based or solvent-based adhesive, depending on the manufacturer’s recommendations and the type of roof substrate.
• Fold back the membrane: Carefully fold back half of the membrane to expose the garage roof surface without moving the other half.
• Spread the adhesive: Using a spray, roller or brush, apply the adhesive evenly to both the roof deck and the underside of the EPDM membrane (unless using peel-and-stick EPDM, which has an adhesive backing). Apply the adhesive in manageable sections to avoid drying out.
• Bond the membrane to the roof: Once the adhesive is tacky (but not wet), roll the membrane back onto the roof and press it down firmly, smoothing out any air bubbles or wrinkles. Use a soft-bristle broom or roller to press the membrane and ensure full adhesion.

Step 6. Repeat for the other half of the garage roof

Once the first half is secured, repeat the process for the other half of the roof. Fold back the unbonded section, apply adhesive, and press the membrane down.

Step 7. Secure the edges

• Trim excess membrane: After the membrane is fully adhered to the roof surface, trim any excess material hanging over the roof edges with a utility knife.
• Install perimeter fixings: Use a termination bar or adhesive to secure the membrane at the roof edges. For a neater finish, you can also use gutter and edge trims to protect the membrane and improve aesthetics.
• Seal the edges: Apply EPDM lap sealant or adhesive around the roof edges and any areas where the membrane may be vulnerable to lifting or water ingress. Press firmly to ensure a watertight seal.

Step 8. Dealing with seams (if applicable)

• Overlap the membranes: If multiple sheets of EPDM are required, overlap them by at least 50–100 mm. This will increase reliability when you waterproof the garage roof.
• Use seam tape: Apply double-sided seam tape to the overlap area to bond the two sheets together. Press the tape firmly, ensuring a tight seal.
• Apply lap sealant: After bonding, apply EPDM lap sealant to the seam edges for extra waterproofing protection.

Step 9. Flashing and roof penetrations

• Install flashing: For roof penetrations like pipes, vents, or skylights, use pre-formed EPDM flashing or cut a custom piece from the membrane. Ensure a snug fit and seal the flashing with adhesive and seam tape as needed.
• Seal penetrations: Use lap sealant around penetrations and flashing to prevent water from seeping in around these vulnerable areas.

Step 10. Inspect the installation

• Check for wrinkles or bubbles: After the installation is complete, check for any bubbles, wrinkles, or air pockets in the membrane. If any are found, press them out with a roller or broom.
• Final inspection: Ensure that all seams, edges, and roof penetrations are properly sealed and that the membrane is securely bonded to the roof surface.

Step 11. Protect the membrane (if necessary)

• If the roof is subject to heavy foot traffic, you may need to install walk pads or protective mats to prevent damage to the EPDM membrane.
• Optional: Consider adding gravel or ballast over an insulating layer if recommended by the manufacturer for your specific type of EPDM membrane.

Key considerations before you waterproof a garage roof with EPDM

• Weather conditions: Install EPDM in dry weather conditions to avoid issues with adhesive bonding or membrane stretching due to temperature fluctuations.
• Use high-quality adhesives: Ensure you use adhesives and sealants compatible with EPDM for a durable and long-lasting installation.
• Roof slope: While EPDM is ideal for flat or low-slope roofs, proper drainage is essential to prevent water pooling. Ensure that your garage roof has sufficient slope and drainage outlets to avoid water accumulation.

By following these steps, you can effectively waterproof a garage roof with EPDM, ensuring long-lasting protection against leaks and moisture damage.

Can we help?

At PermaRoof, we can support how you waterproof a garage roof with EPDM kits, installation guides and an expert team ready to walk you through. Find out more about garage roofing or get in touch today.

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