Moisture mapping flat roofs

Moisture mapping gauges the thermalisation (slowing down) of emitted neutrons to detect hydrogen and therefore moisture content to a depth of 300mm and diameter of 250mm from the gauge base. Roofing materials also contain hydrogen, and so a background reading is established by analysing core samples taken from varying gauge reading locations (low-high) to determine how much of the thermalisation is due to trapped moisture.

Testing Method Key Features 


  • Decisions for roof repair are based on accurate, scientific information rather than assumptions and opinions
  • Ideal for testing multiple roof systems on a roof area, such as those having already been overlaid
  • Multiple layers of insulation
  • Analysis penetration up to 300mm
  • Daytime readings taken
  • All waterproofing systems and ballasted roofs

Moisture mapping survey

Measurements are generally performed in a two metre grid pattern that is plotted on a scaled drawing of the roof. Once readings to all grid points have been taken, a histogram is created to help determine which values represent dry and wet areas.

Moisture mapping is suited for all roof structures, particularly those with multiple layers of insulation and previous waterproofing systems. The gauge will also detect moisture within certain decks or supporting structure in uninsulated roof situations.

Moisture map histogram

Moisture Mapping Plot

Our diagnostic report plots precisely the roof’s condition confirming the suitability of the existing build up to receive a waterproofing membrane overlay and identifying areas that need the insulation to be replaced beforehand.

The red zones indicate high levels of moisture, reducing in concentration through the yellow then blue; these zones will need to be stripped off and insulation replaced before having the new waterproofing installed over the top.  The grey areas are dry and can be easily overlaid.

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