mdm®Ventia Iron Roof & Wall Underlay - Building NZ
mdm®Ventia Iron Roof & Wall Underlay

mdm®Ventia Iron Roof & Wall Underlay

Withstands 90 days UV exposure. High absorbency. Exceptional breathability.

Words by ArchiPro Editorial Team

What is the main purpose of a building underlay ?

Weathertightness, absorbency and breathability.

They are all important, but breathability is paramount.

Humidity in New Zealand is commonly between 70 and 80 per cent in coastal areas and is about 10 per cent lower inland. To that humidity we add the moisture created by common household activities - for example, in a five person home on average 20 litres of moisture is created daily.

If underlays are not breathable enough, water vapour will be trapped in the home and there is a limit to the amount the air can hold for a given temperature. When that limit is reached, the air is said to be saturated. When saturated air comes in contact with a surface that is at a lower temperature than itself, it sheds its surplus water vapour on that surface; condensation takes place. If this happens in the wrong places, it’s not good for you or your home.

For example, in a house with a roof area of 100 sqm, Ventia Iron Roof & Wall Underlay will allow the transfer of 140 litres – 320 litres of water vapour to the exterior plus it has the capacity to absorb 20 litres of water vapour every 24 hours.

Another very convenient property of Ventia Iron Roof & Wall Underlay is its rating for 90 days UV exposure, very handy nowadays with building supply issues and other delays.

Next-generation Ventia Iron Roof & Wall Underlay is manufactured by one of the few companies in the world capable of producing such quality, mdm®NT with its headquarters in Bielsko-Biala, Poland. Meeting and exceeding the strictest European requirements.

For more information, visit us on (

The best possible quality at a very attractive price! BRANZ appraised of course.

Trust the highest quality – enjoy the benefits of our underlays with confidence.

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