Flat roofs, terraces and balconies depend on a single functioning layer. If the waterproofing is defective, water will find its way through, and rarely where the stain appears on the ceiling. Waterproofing contractors install and refurbish this layer, locate leaks and build up the system with falls, insulation, waterproofing and a protective layer.
They install bitumen membranes or synthetic membranes, build up the roof system with a vapour control layer, insulation, falls and a protective layer, connect to upstands, outlets and door thresholds, and create green or gravelled finishes. In refurbishments, leak detection is added before anything is opened up at all.
A flat roof has water lying on it as soon as it rains and is exposed to UV radiation without protection. As a rule of thumb, flat roof waterproofing in bitumen or synthetic membrane lasts around twenty-five to thirty-five years, noticeably less than a tiled roof covering. Blocked drains, standing water and mechanical damage from foot traffic shorten this period even further.
The water stain on the ceiling is almost never directly below the leak, because water travels across the vapour control layer or within the insulation. Specialist contractors locate leaks using moisture measurement, smoke methods or electric pulse methods instead of opening up the roof on suspicion. This assessment costs a fraction of a full-area refurbishment and prevents the wrong spot from being opened up.
For a flat roof with bitumen or synthetic membrane, the guide price is around CHF 120 to 200 per square metre, according to our renovation costs guide. Not included are the formation of falls, additional insulation, flashing work on upstands and disposal of the old roof build-up, which in older buildings may be contaminated with hazardous substances.
Have the complete layer build-up described, not just the waterproofing material. Check whether falls, the vapour control layer, insulation, threshold heights at doors and the outlets are included. Threshold heights are the most common weak point on terraces: if the threshold is too low, water runs into the building during heavy rain, regardless of the quality of the surface.
A flat roof needs inspection. Blocked drains are the most common cause of damage because standing water adds load and finds every weak point. Remove leaves and vegetation growth twice a year, inspect the waterproofing at the upstands and check it after hail: this effort noticeably extends the lifespan and is cheaper than any refurbishment.