Leaks on green roofs’ liner can be identified without installed monitoring system, however, the required conditions usually cannot be met in case of a finished roof. In case of reverse layers, the closed cells insulation boards distort the survey results and the leaks cannot be identified based on surveys performed on the finished the roof. The problem can be avoided if under the waterproofing layer a geoelectrical monitoring system is installed, which occasionally or continuously can monitor the layer’s condition.
On a garage roof we made surveys to test the green roof monitoring system. Our goal was to determine which is the best place of the monitoring system within the roofing layers. 3 different monitoring systems were installed as it can be seen on the figure below. The monitoring system M1 was installed directly on the concrete ceiling, this was covered by a vapour barrier. Above the vapour barrier, the insulation layer was installed, on top of this the monitoring system M2 was installed. Over this the PVC waterproofing layer was set up, on top of that the monitoring system M3 was installed.
Then an artificial leak was cut on the PVC, water was poured on the surface and an automatic measuring device was installed with continuous surveys. After analysing the survey results, it can be stated that the best place of the monitoring system is directly below the waterproofing layer, as the vapour barrier is also an electrically insulating barrier.
On the below pictures an example in practice is shown, where the monitoring system was installed under the PVC waterproofing layer at the green roof of a house under construction.
Copper sensors are installed in a rather symmetrical grid
The location of the sensors is recorded, as during the surveys the sensors with the highest electrical potential indicates the leak
The sensors are connected to a measurement box (installed at the edge of the roof) by insulated copper wire
More sensors are installed at chimneys and other penetrations as these are potential leak sources