Three-ply VHP Roof Underlay by Masons leads to better moisture management

Written by


11 February 2022


3 min read


Even as building technology advances, many roofing contractors and specifiers still rely on traditional bitumen-impregnated paper for their roofing underlay.

The new range of VHP Roof Underlay from Masons offers the superior performance of modern materials and manufacture, outlasting the decades-old technology of black paper.

The main advantage of bituminous paper has always been its low cost. But it can easily tear on installation, may shrink when wet, doesn’t ‘breathe’ very well, and can become dry and brittle with age. It is also flammable.

For as little as $300 extra for an average house, VHP is a more resilient and waterproof product that is simple to install, and building owners get a more breathable and durable underlay.

Three-ply VHP Roof Underlay by Masons leads to better moisture management

Superior moisture management

VHP is a part of Masons’ breathable building wrap system, bringing excellent moisture management to the whole envelope.

Constructed in three layers – a highly vapour-permeable, water-resistant membrane sandwiched between two tough layers of non-woven polyolefin fabric – VHP helps control condensation inside, while channelling water away to the exterior.

Self-supporting, fire-retardant, and with excellent breathability, it is a premium grade roof underlay that combines high performance with competitive pricing.

‘Being micro-porous, VHP underlay transfers water vapour at higher rates than bitumen-impregnated paper,’ notes Masons' Technical Manager Arthur Whitfield. ‘It absorbs condensation, allowing moisture to gradually dry out and pass through the membrane.’

The VHP system complies with and exceeds all the provisions of External Moisture Clause E2 of the New Zealand Building Code.

Three-ply VHP Roof Underlay by Masons leads to better moisture management

Strength and fire protection built in

The VHP range serves to protect buildings and their occupants not just from moisture but also from fire risks. Bituminous paper is a potential fire hazard, whereas VHP acts as a fire-retardant. And, unlike bitumen, its synthetic material will maintain its integrity almost indefinitely, so long as it is kept away from sunlight.

VHP is currently available in three grades – Strong, Ultra and Maxi – each able to support its own weight over 1200mm. It does not always require netting (depending on roof pitch and rafter span), and is rated for up to and including Extra High wind zones. Unlike black paper, it won’t rip or tear during normal handling, making installation quick, easy and more efficient.

The range covers all building types. VHP Strong (140 gsm) is suitable for new residential builds and re-roofs. VHP Maxi (220 gsm) is designed for large commercial premises with longer spans, while VHP Ultra (180 gsm) is ideal for light to medium industrial applications.

Masons is also introducing VHP Value (125 gsm), which is not fire-retardant, and will be available at a price point compatible with traditional black paper.

Three-ply VHP Roof Underlay by Masons leads to better moisture management

Specifying with confidence

All VHP underlays are pH neutral, ensuring they will not react with treated timber, and are compatible with all roofing materials. The range is Codemark-certified and warrantied for up to 50 years.

Masons source their products from the best manufacturers around the globe, specifically for New Zealand conditions. Drawing on this global expertise in flexible wall cladding and roof underlay manufacturing, the VHP range represents one of the best choices for modern construction and optimum performance.

For more information, visit our website, or contact Masons on 0800 522 533.