Testing Through Overburden
Low Voltage Electronic Testing
Low Voltage testing through overburden allows flexibility when a roof or membrane is a green or ballast roof. Even though you may sacrifice pin-point accuracy due to the 3-dimensional testing field, there is no need to rip up sections of the assembly, saving you time and money.
Primarily used as a response to on-going leaks below the membrane, testing through overburden can help identify and narrow the area of discovery for potential breaches in the membrane below.
If leak detection was performed when the membrane was initially installed, a wire loop may have been permanently installed under the overburden to facilitate testing at a later date. If not, a wire loop is placed on either the surface of the overburden or intermittently buried at a shallow depth within the overburden.
The overburden is thoroughly saturated with water in order to ensure that the entire overburden assembly becomes conductive and can support the flow of an electrical current to the membrane below.
One of the two leads from a power supply is connected to this wire loop conductor. The other lead is connected to the structural deck.
As a result, an electrical potential difference is created between the membrane surface, which is wet, and the structural deck, which is “earthed” or grounded – essentially producing two opposing electric plates.
A 16-probe receiver is placed on the saturated surface of the overburden in an approximately 3’ x 3’ pattern.
If readings indicative of a breach are found, additional adjacent readings are taken until an area of concern can be mapped out on the overburden’s surface.
This area of concern is marked on the overburden’s surface, providing a frame of reference for the area of overburden to be removed. Because testing is not occurring directly on the membrane, these areas can range from 10-100 SF in size.
Once the membrane is exposed, standard ELD can be completed directly on the membrane, pinpointing any potential breaches.
Once the breach is located, it is marked on the membrane, photographed, and cataloged for reporting purposes.
We generate and submit a detailed report of our findings, that includes general project information, noted site conditions (with photographs), breach photographs and measured locations. A digital drawing is submitted with the report that highlights the area(s) tested, with all breach locations plotted.
Overburden - Grounded
In figure 1, you will see a traditional low voltage ELD testing process where the electricity is grounded allowing to ELD unit to provide accurate breach detection.
Overburden - Extra Layer
In figure 2, notice the extra layer of insulation that the electricity needs to go through in order to be grounded. Otherwise, this masks breaches.
While testing through overburden provides insight into breaches and leak locations, accuracy may be impacted.
Overburden Spotlight Project
No you aren't looking at the ground -- but actually an overburden roof top.