Monarflex Ventilated roofing underlay

Monarflex Non Breathable Membranes

The Monarflex non breathable membranes are generally comprised of a reinforcing grid of either polyester yarn or polypropylene which is protected by two layers of low density polyethylene (LDPE).

This build–up could also incorporate an additional layer of spun bond that are either hydrophilic (water absorbing) or hydrophobic (water repellent) dependent of the climatic conditions or simply local building tradition.

Non Breathers - construction

Monarflex ventilated roofing membrane portfolio:

  • MONARFLEX® Protect 1F
  • MONARFOL® 100
  • MONARFOL® 145 Plus
  • MONARFOL® Super
  • ICOPAL® Def’x R3T
  • ICOPAL® Def’x Multi

The non breathable membranes can only be used in pitch roof constructions where there are a built-in ventilated gap between the roofing underlay, which is fixed to the roof rafters and the insulation material beneath. The ventilation gap is typically so to avoiding the built-up of moisture.

When constructing the ventilation gap it is crucial that a suitable ventilation opening is made at the eaves level and in the ridge area.

Before choosing the appropriate roofing membrane for your type of construction consider the below points in order to zoom in on the best product to suit your specific needs.

  • What kind of exterior roof material is used? Can UV (sun light) shine in on the roofing underlay or not?
  • The construction type must be considered, is it a ventilated or non-ventilated construction?
  • Is it a boarded or non boarded (only rafters) roof construction?
  • Angle of the roof slope
  • Duration of the construction period where the roofing underlay will be exposed to conditions of the weather e.g. sun light, rain, snow, wind etc.
  • Climate conditions should be considered – condensation build-up during the seasons.
  • Position of the building, e.g. sea site or in land site


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Monarflex contact details

Monarflex s.r.o.
Továrenská 1
943 03 Štúrovo

Slovak Republic

Phone + 421 36 7563865

UK & Ireland

Please visit the dedicated website at

Tel: 0161 8654444 (UK office)

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