Product Description

Covertek 407 is our strongest synthetic underlay, designed as a means of managing condensation, water vapour transfer and water ingress in the most trying conditions. including applications where the roof pitch is 3° and above. 

Covertek 407 is fire retardant.

Scope of use

Roof Application

• Suitable with masonry tile, metal tile and profiled metal roof cladding.
• Suitable for timber or steel framed buildings.
• Can be used on roofs up to and including NZS 3604 Extra High wind zones.
• Self-supporting - Refer to installation guide regarding underlay support requirements.
• Not suitable for roof pitch less than 3 degrees.
• Will provide some temporary weather protection during construction (maximum 7 days), same day coverage recommended.

Wall Application

• Can be used with timber and steel framing, either direct or in conjunction with an 18mm minimum drained cavity.
• Suitable with absorbent (e.g. timber, brick or fibre cement) or non-absorbent wall claddings (e.g. metal or plastic).
• Suitable with masonry veneer in accordance with NZBC Acceptable Solution E2/AS1 or NASH Building Envelope Solutions.
• 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 60 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.

Flammability Index

Thermakraft Covertek 407 Underlay has an AS 1530 Park 2 Flammability Index of not greater than 5 and therefore meets the requirements of the NZBC Acceptable Solutions C/AS2, Paragraph 4.17.8b, 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), 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 7 days (roof) same day coverage recommended.
• Is not left exposed for more than 60 days (wall)
• Is installed by or under guidance of Licensed Building Practitioners.
• Is compatible with cladding system used.*

* Note: specifiers and product user must confirm roof and 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.