The EPDM flat roof has gained a lot of ground in Belgium in recent years, alongside traditional bitumen roofing. When renovating a flat roof, whether on an extension, a garage or a house, the question often comes up: which membrane should you choose? Both solutions are reliable when properly installed, but they do not have the same strengths. Here is our comparison, without bias.
EPDM in a nutshell
EPDM, short for ethylene propylene diene monomer, is a synthetic rubber. It comes in large membranes, often in a single piece for a small roof, which are bonded to the deck or the insulation. Joints are made with special tapes and adhesives, without a flame.
The strengths of an EPDM flat roof
- Flexibility: the membrane copes with building movement and temperature swings without cracking.
- Resistance to UV and ageing, with no additional protection.
- Few joints on small areas, since the membrane can be laid in one piece.
- Flame-free installation, safer on timber decks and near sensitive materials.
- Light weight, an advantage on existing structures.
- Suitable for green roofs, thanks to the good root resistance of many products.
Its limitations
- The quality of installation, particularly the bonding and joints, is decisive.
- The black membrane can be vulnerable to sharp impacts, for example during work on the roof.
- Not all EPDM membranes are equal: thickness and brand matter.
Bitumen roofing in a nutshell
Roofing felt, or modified bitumen, is the traditional technique for Belgian flat roofs. It is generally laid in two layers: an underlayer and a cap sheet, often protected by slate granules. The sheets are torch-welded or cold-bonded depending on the product.
Its strengths
- Robustness: the double layer provides good mechanical resistance and extra security.
- Proven technique, known to every professional.
- Easy repairs, simply by adding bitumen.
- Good tolerance of occasional foot traffic for maintenance.
Its limitations
- Torch-on installation requires precautions on combustible decks.
- Bitumen ages faster under UV if it is not protected.
- The many overlaps multiply the points to watch.
EPDM flat roof or bitumen: the comparison table
| Criterion | EPDM | Bitumen roofing |
|---|---|---|
| Number of layers | One membrane | Generally two layers |
| Installation | Bonded, flame-free | Torch-welded or cold-bonded |
| Flexibility | Very high | Good |
| Impact resistance | Average | Good |
| Repair | With specific kits | Simple |
| Green roof | Very suitable | Possible with a root barrier |
| Indicative price excluding VAT, without insulation | €60 to €100/m² | €60 to €95/m² |
Which choice for which project?
Small extension, annex or garage
EPDM is often the wisest choice: a single membrane, no joint in the middle of the roof and flame-free installation. It is the solution we install most often on Brussels extensions.
A roof with heavy foot traffic or exposed to impacts
On a roof that carries technical installations or is walked on regularly, two-layer bitumen, which is mechanically stronger, remains an excellent choice.
Green roof
EPDM, with the good root resistance of many products, is particularly well suited. Our article on the green roof describes these projects in detail.
What matters most: insulation and detailing
Whatever the membrane, the lifespan of a flat roof depends mainly on three things. First, insulation: in a warm roof, the insulation laid under the membrane protects the structure and improves comfort. Next, the fall: a gradient of 1 to 2% prevents ponding. Finally, the details: upstands that are high enough, well-finished edges, properly sized outlets and overflows. A premium membrane that is badly detailed will leak sooner than an ordinary membrane that is perfectly installed.
Our advice
Never renew the waterproofing of an uninsulated flat roof without insulating it. It is the ideal moment, and insulation under the membrane also extends its lifespan.
How long does a flat roof last?
A quality EPDM flat roof or bitumen roofing, installed properly and maintained, commonly lasts several decades. Manufacturers often quote long lifespans, but in reality it depends on exposure, foot traffic on the roof and the upkeep of the outlets.
Maintaining your flat roof
- Remove leaves and debris twice a year.
- Check that outlets and overflows are clear.
- Visually inspect the upstands and edges.
- Avoid walking on the membrane in hard-soled shoes, and do not leave sharp objects on it.
- Have the roof inspected after a storm.
Solar panels on an EPDM flat roof
Many owners take advantage of a flat roof renovation to install solar panels. On EPDM as on bitumen, ballasted mounting systems avoid piercing the membrane. Where penetrating fixings are needed, they must be made with sealing pieces compatible with the membrane. Also plan walkway tiles for panel maintenance so that the waterproofing is not damaged. We coordinate these details with your installer.
Colour and summer comfort
EPDM is usually black, which absorbs a lot of heat in summer. On a well-insulated warm roof, this has little effect on the room below, but on a poorly insulated extension the difference can be noticeable. Lighter membranes and reflective coatings are also available, and a green roof or a layer of gravel keeps the membrane cooler. We discuss these options with you when comfort under the roof is a priority.
Frequently asked questions
Can EPDM be laid over old roofing felt?
It is sometimes possible if the substrate is sound, dry and compatible, with a separation layer. But if the roof is not insulated or the old build-up is damp, it is better to strip everything.
Is an EPDM flat roof noisy in the rain?
No. Noise depends mainly on the structure and the insulation. A well-insulated warm roof greatly reduces the sound of rain.
Can you walk on an EPDM roof?
For maintenance, yes, with care. For regular use, such as a terrace, suitable protection is needed: paving slabs or boards on pedestals.
In summary
The EPDM flat roof is ideal for small areas, extensions and green roofs; bitumen roofing remains unbeatable for robustness. In both cases, insulation and detailing matter more than the membrane. Our roofers install both solutions in Brussels, Walloon Brabant, Hainaut and Flanders: discover our flat roof service and request a free quote.
