Mold source detection with theGerman Flag
gO Measurement System

Mold growth is determined by the surface water activity, the relative air humidity, and the duration of wetting. According to SIA 180 and DIN EN 1804, to avoid the risk of mold the surface moisture (relative humidity) should not exceed the value of 80% more than two consecutive weeks per year.

The relevant values for these parameters can easily be measured with greenTEG’s gO Measurement System. The gO Measurement Systems is a cloud-based multichannel tool for wireless temperature and humidity measurements. The system provides you with the accurate RH, aw, and temperature values you will need to detect sources of mold. All measurements can be monitored remotely in real-time.

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Aw-value measurements for mold detection


The water activity measures the amount of free water available for mold growth at the nutrient surface. The surface humidity is the humidity directly at the surface of a wall and cannot be measured. However, by measuring room temperature, room humidity and surface temperature, the aw-value can be determined and considered as the humidity at the surface. The Aw values range from 0 to 1.0 and are unitless. If the aw-value is 0.8, the surface humidity will be at 80%.

According to the norms for new buildings, the surface humidity on an outside facing wall should not succeed 80% relative humidity. Therefore, a water activity measurement is the most appropriate test to determine if the wall is damp enough to support the growth of mold.

But how to measure water activity? With the gO Measurement System, it is possible to calculate the water activity at the surface of a wall. Our measurement approach uses a humidity sensor and two temperature sensors. The data is sent to the cloud with a secure 3G connection. This allows for continuous real-time remote monitoring of reliable in-situ information about a given building envelope.

For a holistic inspection of your building envelope condition, we also offer a  U-value, R-value and heat flux measurements solutions to assess insulation quality and detect thermal bridges. 

More about the gO Measurement System

Detect mold-prone spots

Mold detection

The growth and proliferation of microorganisms is controlled by water activity and the critical aw-value for mold is 0.8. With the gO Measurement System you can provide hard data as evidence for mold-prone spots to suggest counter measures.

Surface humidity (aw-value) can be determined by measuring:

  • Room humidity
  • Room temperature
  • Surface temperature 

Live observation of the aw-value:

  • Share the live view with customers for demonstration
  • Detect and record any attempts for manipulation of the measurement 

Humidity control

Controlling humiditiy is an important factor for mold free storage. With the gO Measurement System you can measure humidity even in difficult to reach spots and monitor it continuously in real-time.


  • Continuous monitoring is often not possible due to the location of the storage (basement, attics)
  • Standard control on a dehumidifier is not accurate due to humidity distribution in the room  


  • Up to 16 humidity sensors can be placed anywhere in the building
  • Due to the special signal tuning of the gO Measurement-System, live data are anywhere and anytime accessible via the web cloud

Resources: mold detection case studies

Download our case studies where we show what kind of insights you will get when making measurements with the gO Measurement System.

Mold on the outer wall: structural defect or insufficient ventilation by the tenants?

This study shows how a heat flux and humidity measurement with the gO Measurement System can be used to identify the reason for mold growth.

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U-value and dewpoint assessment with the gO Measurement System

The purpose of this study is to measure the U-value, the temperature and the humidity levels (RH) of the interior of a single-family apartment to examine the influence of these factors to the formation of mold.

View PDF 


Wall humidity and U-value measurements for mold detection

The purpose of this study is to show how the gO Measurement-System (gOMS) can be used to measure the humidity of the wall and the U-value as well as how the combination of this data can help to analyze and prevent mold growth.

View PDF


More about the gO Measurement System

Video: how to set-up a measurement


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