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Construction Membranes: ProctorWrap IRMA

ProctorWrap IRMA

ProctorWrap™ IRMA is designed for use as a separating layer in ballasted or paved Inverted Roof Membrane Assembly (IRMA) flat roofs. ProctorWrap™ IRMA acts as a filter layer preventing fines and other debris from passing through, and also as a water flow reducing layer minimising cold rainwater flowing between the insulation and the roof waterproofing thus reducing the consequent rainwater cooling effect.

Rainwater that penetrates IRMA roof systems reaching the waterproof layer can impact on the thermal performance of the construction. To take account of this loss in thermal performance, the initial R-value of the roof should be corrected by subtracting a rainwater correction factor (determined using the method described in BS EN ISO 6946:2007) dependent on local rainfall and the proportion of rainwater reaching the waterproof layer under the insulation.

This can be substantially reduced by incorporating ProctorWrap™ IRMA as a water-flow reducing layer directly above the insulation, to drain rainwater off the roof before it reaches the waterproof layer.

ProctorWrap™ IRMA is impermeable to liquid water and substitutes conventional fleece filter fabrics that do not perform as an effective water draining separation layer.


  • As a vapour permeable separating and water control layer for use in Inverted Roof Membrane Assembly (IRMA) systems.

Technical data

  Resistance to water penetration:   Class WI
  Resistance to water penetration after artificial ageing:   Class WI
  Flexibility at low temperature:   -20°C
  Tensile strength after artificial ageing:
  > 170/100 N/5cm
  Resistance to tearing:
  > 60/70 N
  Resistance to the effects of lime water, sodium 
  chloride solution and sulphurous acid:
  Hydrostatic pressure:   > 2.5m
  Available roll dimensions:   3m x 100m
  Colour:   Dark Grey


  • High vapour permeability
  • Water resistant up to 2.5m head of water
  • UV stable for up to 2 months exposure in Australia and NZ
  • Resistance to the effects of lime water, sodium chloride  solution and sulphurous acid in concentrations required by EN 1847
  • Strong, yet lightweight for ease of application
  • Resistant to mould

Available in 3m wide rolls to reduce overlaps


ProctorWrap IRMA (PDF)

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