EPDM (Ethylene Propylene Diene Monomer) is a synthetic rubber used as waterproof roofing on flat and low-pitch roofs. The material is laid as a single large sheet over the roof and bonded with adhesive, creating a seamless, watertight seal. EPDM is the most popular roofing material for flat roofs in DIY projects.
Why EPDM?
| Advantage | Explanation |
|---|---|
| DIY-friendly | One sheet, bonded with contact adhesive — no torch needed |
| Long lifespan | 40-50 years with proper installation |
| Flexible | Moves with the structure, does not tear |
| UV-resistant | Does not degrade from sunlight |
| Temperature-resistant | -40°C to +120°C |
| Low maintenance | Virtually no maintenance required |
Where is EPDM used?
- Flat roofs — The main application: garages, garden sheds, outbuildings, extensions
- Low-pitch mono-pitch roofs — At less than 15° pitch
- Dormer windows — Flat top and cheeks
- Ponds — EPDM is also used as pond liner (different grade)
Structure of an EPDM roof
From bottom to top:
1. Supporting structure — Timber joists
2. Roof decking — 18 mm plywood or OSB (smooth, no irregularities)
3. Vapour barrier — Membrane on the underside of the insulation
4. Insulation — PIR boards (with a slope for drainage)
5. EPDM membrane — The waterproof sheet
6. Edge finishing — Drip edge or fascia board with EPDM folded over
Laying EPDM yourself
Preparation
- Substrate must be clean, smooth, and dry
- No screw heads or splinters that could puncture the rubber
- Lay the EPDM out in the sun for an hour to make it supple
Steps
1. Unroll the EPDM — Lay the sheet over the roof with 10-15 cm excess on all sides
2. Fold back half — Fold one half back
3. Apply contact adhesive — On both the roof and the EPDM membrane
4. Flash-off time — Wait until the adhesive “dries” (no longer sticks to your finger, but still tacky)
5. Press down — Roll the EPDM from the centre to the edge, push out air bubbles with a roller
6. Other half — Repeat for the second half
7. Finish edges — Fold over the fascia board, secure with EPDM sealant or clamping strip
8. Penetrations — Rainwater outlets, ventilation pipes: seal with EPDM collars
Tools
- Wide roller (wallpaper roller or EPDM roller)
- Brush or roller for adhesive
- Stanley knife
- EPDM contact adhesive (specifically for EPDM — not regular contact adhesive)
EPDM vs. bitumen
| EPDM | Bitumen | |
|---|---|---|
| Installation | Bonding (cold) | Torching (hot) or self-adhesive |
| DIY | Very doable | Torching = risky for amateurs |
| Seams | None (single sheet) or bonded | Overlapping strips |
| Lifespan | 40-50 years | 20-30 years |
| Flexibility | Very flexible | Less flexible (can crack in cold) |
| Price per m2 | EUR 10-15 | EUR 5-10 |
Common mistakes
- Insufficient flash-off time — If you press down too soon, the adhesive does not bond properly
- Air bubbles — Always work from the centre to the edge, not from the edge to the centre
- Wrong adhesive — Use EPDM-specific contact adhesive. General-purpose adhesive will fail.
- Sharp edges — A screw head or splinter in the roof decking will puncture the EPDM over time
Related terms
- Flat roof
- Bitumen
- Slope (drainage gradient)
- Fascia board
- Gutter
- PIR insulation