COVERTEK 403
Non self-supporting roof and wall underlay.
Covertek 403 is a fire retardant, light weight roof and wall underlay designed as a
means of managing condensation, water vapour transfer and water ingress. Primarily developed as a roof underlay, Covertek 403 can also be used on walls if you are after a one stop solution. It is not self-supporting as a roof underlay and is a more affordable option where a supporting component is to be installed in the building.
Technical Downloads
Product Specifications
Covertek 403 comes in three roll sizes:
| Width | Length | Coverage |
|---|---|---|
| 1350mm wide | 18.6m long | 25m² Coverage* |
| 1350mm wide | 37m long | 50m² Coverage* |
| 1350mm wide | 56m long | 75m² Coverage* |
* Note: m² is the roll size for actual coverage, allow for laps and joins.
Scope of use
Roof Application
- Can be used with lined timber and steel frame buildings.
- Suitable with masonry tile, metal tile and profiled metal roof cladding.
- Can be used on roofs up to and including NZS 3604 ‘Extra High’ wind zones.
- Covertek 403 requires underlay support (not self-supporting).
- Will provide temporary weather protection during construction (maximum 7 days roof application), same day coverage recommended.
Wall Application
- Can be used with lined timber and steel frame buildings, either directly fixed or in conjunction with an 18mm minimum drained cavity.
- With absorbent claddings (e.g. timber, brick or fibre cement) or non-absorbent wall claddings (e.g. metal or plastic).
- Is suitable for use in Wind Zones of NZS 3604 up to and including ‘Very High’ when used as a standalone flexible underlay, and ‘Extra High’ when used as a flexible underlay over a rigid wall underlay.
- Is suitable as an air barrier in unlined wall spaces.
- Will provide some temporary weather protection during construction (maximum 42 days for wall application).
General
- Is fire retardant.
- Unaffected by LOSP or other solvent based treated timber. However, LOSP or other solvent based treated timber must have sufficient time for the solvent to flash off in a well ventilated area. Recommended minimum 7 days.
- Tear resistant and strong.
Limitations
- Cannot be exposed to the weather or UV for more than 7 days as a roof underlay and 42 days as a wall underlay.
- Can only be used as a Roof underlay on roofs of 10° pitch or greater.
- Must be used with underlay support products in roof application.
- Must not be used under translucent roof sheeting.
Compliance
Roof Application
- Covertek 403 can be used as a roof underlay within the scope limitations of NZBC Acceptable Solution E2/AS1, Paragraph 1.1, with regards to building height and floor plan area.
- Refer BRANZ Appraisal No 917 (2020) and CodeMark Certificate GM-CM30030 for full details.
Flammability Index
Thermakraft Covertek 403 Underlay has an AS 1530 Part 2 Flammability Index of not greater than 5 and therefore meets the requirements of NZBC Acceptable Solution C/AS2, 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.
Durability
Meets the Performance Requirements of NZBC Clauses B2, Durability (B2.3.1 (a) 50 years, B2.3.1 (b) 15 years and B2.3.2), and F2.3.1, providing:
- It is not damaged.
- Is installed in accordance with instructions.
- Is not left exposed for more than 7 days (roof), same day coverage recommended.
- Is installed by or under guidance of Licensed Building Practitioners.
- Is compatible with cladding system used.*
* Note: specifiers and product user must test for wall cladding system compatibility with the underlay before installation.
Control of Condensation
In climatic regions where condensation risks are high, such as cold or high humidity areas, care needs to be taken in specifying the correct design and installation to prevent moisture build-up in the roof cavities.
Factors which adversely affect the condensation risk in roofing systems include:
- Humid, and/or cold climatic regions.
- Warm/Skillion roof construction.
- Low roof cavity air volume and restricted air movement.
- Omitting Vapour Control Layers.
- Occupancy activities which have high moisture loading on conditioned spaces.
- Ceiling penetrations and entry of warm air into roof cavities.
- Low pitched roof.
- Bulk insulation.
- Building structures ability to naturally dry construction moisture.
Skillion and Warm Roof Construction are particularly sensitive to moisture accumulation and the design and installation of roof construction needs to take into account the higher condensation risks. Refer to the NZ Metal Roof and Wall Cladding Code of Practice (COP) for details.
For passive ventilation of the roof space, it is recommended that all roof underlays are terminated at the ridge, and if not it should be slit or slotted to allow for passive ventilation. For further information refer to the NZ Metal Roof and Wall Cladding COP.
Product Warranty
Standard Thermakraft warranty applies. Refer to Thermakraft Warranty Statement for further details. This item is available online here or call 0800 806 595.
Product Performance
| NZBC E2/AS1 Table 23 (NZ2295)Wall Underlay Properties | Absorbency | Vapour Resistance | pH of Extract | Shrinkage | Water Resistance | Air Resistance |
|---|---|---|---|---|---|---|
| Property Performance Requirement | ≥ 150gsm | ≤ 7 MN.s/g | ≥ 6 and ≤ 9 | ≤ 0.5% | ≥ 100mm | ≥ 0.1 MN.s/m3 |
| Property Performance | Pass | Pass | Pass | Pass | Pass | Pass* |
* Note: Can be used as an air barrier.
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