The flat roof is everywhere in Belgium: kitchen extensions on Brussels houses, garages, recent extensions, apartment blocks and contemporary villas. Yet it has a bad reputation, because many old flat roofs were laid without insulation, with upstands that were too low or drainage that was inadequate. When it is well designed and well built, however, a flat roof is just as reliable as a pitched roof. For 15 years, Toiture En Ligne has been renovating and waterproofing flat roofs in Brussels, Walloon Brabant, Hainaut and Flanders.
Signs that a flat roof needs renovating
- blisters, cracks or wrinkles in the roofing felt;
- puddles that remain for more than 48 hours after rain;
- open seams along the upstands and edges;
- damp patches on the ceiling of the room below the roof;
- a mineral-surfaced membrane that is losing its granules and exposing the base layer;
- a cold ceiling in winter, a sign of missing or insufficient insulation.
A single leak can often be repaired. But if the membrane is more than twenty or twenty-five years old and the roof is not insulated, a complete renovation is usually more economical in the medium term. Our article on what to do about a roof leak helps you react in an emergency.
The waterproofing materials we install
EPDM membrane
EPDM is a synthetic rubber membrane laid in a single piece or in large bonded sheets. Flexible and resistant to UV light and temperature changes, it is installed without a flame, which reduces risks on site. It is particularly suitable for small and medium-sized roofs, extensions and green roofs.
Bitumen felt
Modified bitumen, laid in two torch-on or cold-bonded layers, is a proven and robust solution. The top layer is often protected by slate granules. It is easy to repair and copes well with occasional foot traffic for maintenance.
Other solutions
For some projects, we also offer synthetic TPO or PVC membranes, or liquid waterproofing for complex details. Our comparison of an EPDM flat roof or bitumen felt sets out the advantages of each material.
Insulating your flat roof: the warm roof
Renovating a flat roof without insulating it is a missed opportunity. We apply the warm roof principle, which is the most reliable in our climate:
- a vapour barrier laid on the deck, to stop indoor moisture from migrating into the insulation;
- rigid insulation boards, usually PIR or high-density rock wool, laid in one or two layers;
- a waterproofing membrane, EPDM or bitumen, bonded or mechanically fixed above the insulation.
The insulation therefore stays warm and dry, and the structure is protected from temperature fluctuations. We aim for a thermal resistance of at least R = 4.5 m²K/W, often achieved with 10 to 12 cm of PIR. See also our roof insulation page.
Falls matter, even on a flat roof
A flat roof is never perfectly flat: a fall of 1 to 2% directs water towards the outlets. When the deck has no fall, we create one using tapered insulation boards.
The details that make a flat roof watertight
Most leaks on a flat roof do not come from the surface of the membrane but from the details. We pay particular attention to them:
- The upstands along the walls, raised to a sufficient height and protected by a flashing;
- the roof edges, finished with aluminium or zinc trims;
- the outlets and overflows, sized for heavy rainfall;
- the penetrations: rooflights, lantern lights, chimneys, vents and solar panel supports;
- the junctions with the pitched roof or the neighbouring facade.
How a flat roof renovation works
- Visit, core sample of the old roof build-up and inspection of the deck.
- Detailed quote: strip-off, insulation, membrane, edges, outlets and rooflights.
- Removal of the old waterproofing, or overlaying if the base is sound and dry.
- Installation of the vapour barrier and insulation, with falls created if necessary.
- Installation of the membrane and completion of all the upstands.
- Edge finishing, zinc junctions and a drainage test.
- Handover, photos and written guarantees.
Most flat roof renovations on an extension or garage are completed in two to five days.
How much does a flat roof cost?
| Work | Indicative price range excluding VAT |
|---|---|
| New EPDM membrane without insulation | €60 to €100 per m² |
| New two-layer bitumen felt | €60 to €95 per m² |
| Complete renovation with PIR insulation | €110 to €180 per m² |
| Replacement of a rooflight | quoted according to size |
On small surfaces, the edges, upstands and drainage account for a large share of the budget, so the price per square metre is higher. For a home that is more than ten years old, reduced VAT at 6% may apply.
Going further: green roofs and roof terraces
A renovated flat roof can become a useful space. A green roof holds back rainwater, protects the membrane from UV light and improves summer comfort. A roof terrace adds an outdoor living space, provided the structure allows it. Discover our roof terrace and green roof page and our article on the green roof.
Flat roofs and solar panels
Many homeowners combine the renovation of their flat roof with the installation of solar panels. We then provide ballasted systems or suitable supports that do not needlessly puncture the waterproofing, together with walkway tiles for maintenance. This keeps your new membrane protected and allows the installer to work safely. We coordinate the schedule with the installer so that the panels are mounted on a properly insulated, watertight roof.
Why entrust your flat roof to us?
Our teams finish every upstand and every junction with the same care as the main surface, and send you photos of every stage. You receive a written guarantee on labour and materials, together with the technical data sheets for the membrane and insulation installed.
Maintaining your flat roof
Once or twice a year, in spring and autumn, it is enough to remove leaves and debris, check that the outlets are clear and take a look at the upstands. This simple maintenance prevents most leaks. We also offer inspection visits, especially after a storm.
Frequently asked questions
How long does a flat roof last?
A quality EPDM membrane or bitumen felt, properly installed and maintained, commonly lasts several decades. The quality of the upstands and drainage matters as much as the material itself.
Can a new membrane be laid over the old one?
Sometimes, if the base is sound, dry and compatible. But if the roof is not insulated or the old build-up is damp, a full strip-off is preferable.
Can solar panels be installed on a flat roof?
Yes, on ballasted or fixed supports, without puncturing the membrane unnecessarily. We coordinate the waterproofing with the installer.
