How to Install an EPDM Flat Roof

Tools and Materials

Before You Start

• Check the deck is sound — replace any rotten timbers and fix loose boards
• Ensure the roof has adequate falls (minimum 1:60, ideally 1:40) for drainage
• Install drip edges and gutter before laying the membrane
• Unroll the membrane and allow it to relax flat for at least 30 minutes
• Check the weather — adhesive requires dry conditions and temperatures above 5°C
• Remove all protruding nails and screws from the deck surface

Step-by-Step Installation

1. Step 1 — Prepare the deck. Sweep the deck clean. Remove any dust, debris, or loose material. Check all boards are secure and flat. Fill any gaps or holes with exterior filler. The surface must be smooth — any imperfection will show through the membrane.
2. Step 2 — Dry-lay the membrane. Unroll the EPDM membrane across the roof, allowing it to overlap the edges and upstands by at least 150 mm. Allow the membrane to relax and flatten for 30 minutes. Do not cut to size yet.
3. Step 3 — Fold back half the membrane. Fold the membrane back on itself to expose half the deck. Take care not to crease the membrane.
4. Step 4 — Apply adhesive to the deck. Using a medium-pile roller, apply water-based bonding adhesive evenly to the exposed deck surface. Apply at the manufacturer's coverage rate (typically 1 litre per 2-3 m²). Allow to become touch-dry (20-40 minutes depending on temperature).
5. Step 5 — Apply adhesive to the membrane. Apply the same adhesive to the back of the folded membrane section. Allow to become touch-dry. Both surfaces must be touch-dry before bonding — test with a clean finger.
6. Step 6 — Bond the first half. Carefully roll the membrane back onto the deck, pressing firmly from the centre outward to expel air. Use a soft broom or hand roller to ensure full contact. Avoid trapping air bubbles.
7. Step 7 — Repeat for the second half. Fold back the unbonded half, apply adhesive to both surfaces, allow to dry, and roll back into position. Press firmly for full contact.
8. Step 8 — Detail the edges. Using contact adhesive, bond the membrane into the edge trim channels. Trim excess membrane with a hooked blade. Seal with EPDM-compatible sealant. At upstands, dress the membrane up the wall, fix with a termination bar, and seal the top edge.
9. Step 9 — Seal penetrations. For pipe penetrations, fit purpose-made EPDM pipe boots. Bond them to the membrane with contact adhesive, ensuring a watertight seal around the full circumference.

Common Mistakes

• Bonding before the adhesive is touch-dry — creates bubbles and poor adhesion
• Trapping air bubbles — work from centre outward; bubbles are very difficult to fix afterwards
• Cutting the membrane too short at upstands — allow 150 mm minimum, more is better
• Using non-EPDM-compatible sealants or adhesives — some solvents attack EPDM rubber
• Installing on a wet or dusty deck — adhesive will not bond properly
• Insufficient roof falls — standing water accelerates degradation even on EPDM

Cost Estimate (2026)

Related Calculators

Use the EPDM Roof Calculator for membrane and adhesive quantities, or the Flat Roof Membrane Calculator for alternative membrane options.