Bitumen is a waterproof roofing material consisting of sheets impregnated with bitumen (a petroleum product) that are applied in overlapping layers onto a flat roof. It is one of the oldest and most widely used materials for flat roofs. Bitumen is applied by heating the underside with a gas torch, causing it to melt and bond to the substrate.
Types of bitumen roofing
APP bitumen (plastomer)
- Applied with a torch (torched on)
- Good resistance to UV and high temperatures
- Less flexible at low temperatures
- Most common in Southern Europe
SBS bitumen (elastomer)
- More flexible, even at low temperatures
- Better resistance to structural movement
- Standard in the Netherlands and Northern Europe
- Available as torch-on and self-adhesive
Self-adhesive bitumen
- No torch needed — remove protective film and press down
- Safer and more DIY-friendly
- Weaker bond than torched bitumen
- Suitable for small surfaces (garden building, small shed)
Build-up
A bitumen roof is usually applied in two layers:
1. Base layer — First bitumen sheet, fastened to the roof deck (mechanically or torched)
2. Top layer — Second bitumen sheet with slate chippings or mineral finish (UV protection)
The sheets overlap at least 10 cm, ensuring no seam is left open.
Bitumen in DIY projects
When to choose bitumen?
- Budget — Bitumen is cheaper than EPDM per m2
- Small surfaces — Shed, garden building, lean-to
- Renovation — Torch over existing bitumen (provided the old layer is still in good condition)
Laying it yourself
Torching bitumen requires experience and a gas torch. This carries a fire risk. For DIYers, self-adhesive bitumen is the safest alternative:
1. Clean the roof deck and optionally apply primer
2. Roll out the base layer and secure it
3. Roll out the top layer with 10 cm overlap
4. Press down firmly with a roller
5. Finish and seal the edges
> Note: Torching bitumen is specialist work. Incorrect use of the torch creates a risk of fire and personal injury. Consider EPDM as a DIY alternative.
Bitumen vs. EPDM
| Bitumen | EPDM | |
|---|---|---|
| Price per m2 | EUR 5-10 | EUR 10-15 |
| Lifespan | 20-30 years | 40-50 years |
| Installation | Torch or self-adhesive | Contact adhesive |
| DIY | More difficult (torching) | Easier |
| Seams | Yes (overlapping sheets) | No (single sheet) |
| Flexibility | Moderate | Very good |
| Repair | Simple (torch a patch over it) | More difficult (gluing) |
Related terms
- EPDM
- Flat roof
- Slope (fall)
- Fascia board
- Gutter