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Thermakraft CoverTek 403 — Roof and Wall Underlay

CoverTek 403 Roof and Wall underlay is a fire retardant, absorbent and breathable synthetic roof and wall underlay, constructed using a microporous water-resistant film sandwiched between two layers of shrink-resistant spun-bonded polyolefin. Designed as a means of managing condensation, water vapour transfer and water ingress in roof and wall applications.

Key Features
  • Fire retardant
  • Unaffected by LOSP treated timber
  • Recyclable with no VOCs
  • Tear resistant, lightweight and strong
  • Suitable as an air barrier in unlined walls
Categories / Ranges
Wraps, Underlays and DPCs Roof Wall
Scope of Use

Suitable for use as a roof underlay:

  • NZS 3604: when used as a roof underlay is suitable for use all wind zones, up to, and including, Very High
  • Suitable with masonry tile roof cladding
  • With metal tile and profiled metal roof cladding
  • Can be used as a roof underlay on roofs of 10 degrees pitch or greater. Requires support
  • Will provide temporary weather protection during construction (roofs 7 days) same day coverage recommended
  • May be installed in adverse conditions
  • May be run to any length, including under dark coloured roofs
  • Has a 150mm lap line printed on each edge

Suitable for use as a wall underlay: 

  • NZS 3604: when used as standalone flexible underlay — up to, and including, Very High
  • NZS 3604: when used as a flexible underlay over a rigid wall underlay — up to, and including Extra High
  • Can be used as a wall underlay on timber and steel framed buildings with absorbent and non-absorbent wall cladding direct fixed to framing
  • Can be used as a wall underlay on timber and steel framed buildings with absorbent and nonabsorbent wall cladding installed over an 18mm minimum drained cavity
  • Will provide temporary weather protection during construction (walls maximum 42 days)
  • Can be used as a non-rigid backing material for stucco plaster
  • May be used as a slip layer over rigid backing for stucco
  • Is suitable as an air barrier in unlined walls
Limitations on Use
  • Requires support when used as a roof underlay at all pitches
  • Not suitable for use below 10°

Contributes to meeting the Performance Requirements of NZBC Clauses B2, Durability (B2.3.1 (a) 50 years, B2.3.1 (b) 15 years and B2.3.2), E2 External Moisture E2.3.2), and F2 Hazardous Building Materials F2.3.1, providing:

  • It is not damaged
  • Is installed in accordance with instructions
  • Is not left exposed for more than 42 days (wall), 7 days (roof), same day coverage recommended
  • Is installed by or under guidance of Licensed Building Practitioners
  • Is compatible with cladding system used
NZS 3604 Wind Zone Very High suitable
Very High WInd Zone
Statement of Building Code Compliance

Clause B2 Durability: Performance B2.3.1 (a), not less than 50 years, B2.3.1 (b), 15 years and B2.3.2

Clause C3 Fire Affecting Areas Beyond The Fire Source: Performance C3.4 (c). Thermakraft CoverTek 403 Plus meets this requirement

Clause E2 External Moisture: Performance E2.3.2. When used as part of the cladding system, Thermakraft CoverTek 403 Plus will contribute to meeting this requirement

Clause F2 Hazardous Building Materials: Performance F2.3.1. Thermakraft CoverTek 403 Plus meets this requirement and will not present a health hazard to people

Flammability Index

Thermakraft CoverTek 403 Roof and Wall Underlay has an AS 1530 Part 2 flammability Index of not greater than 5 and therefore meets the requirements of NZBC Acceptable Solutions C/AS2 to C/AS6, Paragraph 4.17.8 b), for the surface finish requirements of suspended flexible fabric used as an underlay to exterior cladding that is exposed to view in occupied spaces. It may therefore be used with no restrictions in all buildings.

Other Performance Attributes
  • BRANZ appraisal # 917 (Roof)
  • BRANZ appraisal # 918 (Wall)
  • CodeMark Certificate 30069
B2 Durability compliant
C Protection from Fire compliant
Protection from Fire
E2 External Moisture compliant
External Moisture
F2 Hazardous Building Materials compliant
Hazardous Building Materials
BRANZ Appraised
BRANZ Appraised
Data Sheet

Issue 4, Nov 2019

Quick Reference Guide

Issue 2, Nov 2019

CodeMark Certificate


Data Sheet: Thermakraft One Wrap System

Issue 4, Nov 2019

Independent Appraisal (BRANZ) - Roof

No.917 [2016] 13 Feb 2020

Independent Appraisal (BRANZ) - Thermakraft One Wrap System

No.962 [2017] 28 Aug 2019

Independent Appraisal (BRANZ) - Wall

No.918 [2016] 13 Feb 2020

Thermakraft Warranty Statement

Issue 2, Nov 2019

Installation and Operation

Issue 1, Nov 2019

Thermakraft Ltd are a leading New Zealand manufacturer of Synthetic and Bituminous underlays for the roof and wall with over 30 years experience

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