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HYDRA Roof Underlay

HYDRA is a heavy duty, spun-bonded, self-supporting, fire retardant, non woven fabric, laminated with a breathable coating for use under roof claddings. HYDRA is a synthetic, tri-laminate underlay suitable for use with timber and steel framing. Also suitable with most roof cladding types including pressed metal, concrete and clay tiles, profile metal roofing. HYDRA is coloured blue and is branded with HYDRA logo, for easily identification on-site.

Key Features
  • Self-supporting
  • Fire retardant
  • Breathable
  • Absorbent
  • Synthetic tri-laminate
  • High tear strength
  • Flammability Index: <5
Scope of Use

HYDRA Roof Underlay has been appraised for use as a roof underlay on buildings within the following scope:

  • the scope limitations of NZBC Acceptable Solution E2/AS1 Para 1.1 with regards to building height and floor plan area; and
  •  with masonry tile roof cladding; or,
  •  with metal tile and profile metal roof cladding; and
  •  situated within NZS3604 Wind Zones up to and including Extra High.

HYDRA Roof Underlay has also been approved for use on buildings subject to specific weathertightness design.  Building designers are responsible for building design and for the incorporation of HYDRA roof underlay into their design in accordance with the declared properties and the instructions of Marshall Innovations Ltd.

Limitations on Use
  • Suitable for residential and commercial buildings with min. roof pitch 3 degrees
  • HYDRA must not span unsupported more than 1200mm in one direction
  • At roof pitches 10° or more HYDRA Roof Underlay may be vertically or horizontally
  • At roof pitches less than 10° (min 3°) HYDRA Roof Underlay may be run horizontally, or vertically if installed over a roof underlay support (refer BRANZ Appraisal Table 2 for support requirements)
NZS 3604 Wind Zone Extra High suitable
Extra High Wind Zone
Statement of Building Code Compliance

In the opinion of BRANZ, HYDRA Roof Underlay, if designed, used, installed and maintained in accordance with the statements and conditions of Appraisal 1071 [2019], will meet, or contribute to meeting the following provisions of the NZBC:

  • Clause B2 DURABILITY: Performance B2.3.1 (a), not less than 50 years, B2.3.1 (b) 15 years and B2 .3.2 HYDRA Roof Underlay will contribute to meeting this requirement
  • Clause E2 EXTERNAL MOISTURE: Performance E2.3.2. When used as part of the roof cladding system, HYDRA Roof Underlay will contribute to meeting this requirement
  • Clause F2 HAZARDOUS BUILDING MATERIALS: Performance F2.3.1. HYDRA Roof Underlay meets this requirement and will not present a health hazard to people

See Appraisal for full information

In-Service History

This product is to New Zealand — installations began early 2020.

B2 Durability compliant
E2 External Moisture compliant
External Moisture
F2 Hazardous Building Materials compliant
Hazardous Building Materials
BRANZ Appraisal: HYDRA Roof Underlay

1071 [2019]

BRANZ Appraisal: Weatherization System

621 [2020]

HYDRA Roof Underlay Installation
Additional Information

Marshall Innovations provide weathertight solutions from below ground to pre-cladding.

Product Enquiries

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