Increasing Airflow in Skillion Roofs

Skillion roof design continues to be a popular choice in the New Zealand domestic housing market, however, the limited natural ventilation of these designs is still not receiving the attention needed. There are still new projects that have missed the memo about moisture and ventilation issues in skillion roofs, and most of the time this comes down to not providing sufficient and well-designed ventilation.

When not handled correctly, moisture trapped in the roof space — either from building materials drying out or from living areas below, will undoubtedly result in mould, moisture, structure and insulation issues and consequent problems for the occupants.

In recent years, there has been an increase in new ventilation products such as castellated battens, honeycomb-style PVC battens, ridge and eave vents. These products can help improve the airflow and reduce the moisture problems often seen in small roof spaces.

With skillion roof design, Thermakraft's recommendation is to first prevent moisture from living areas getting into the roof space. Provision must then also be made to ensure that any moisture that does reach the roof space is adequately ventilated out of the roof area. When ventilated type battens are used in skillion roofs, they should be installed below the underlay and above the rafter/purlin. This will increase airflow and reduce trapped air.

Good design along with Thermakraft’s CoverTek range of high strength high-performance synthetic roof underlay’s and Vapor Shield-101 vapour barrier for high moisture control will assist in preventing moisture problems. Thermakraft's technical team works with designers to select the best underlay for each project.

Talk to Thermakraft about upcoming projects to find out which Thermakraft underlay is best for each design.

Thermakraft Vapour Shield

Kingspan Thermakraft

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Vapour Shield is intended for use as a vapour barrier layer ideally for skillion roof construction where condensation and moisture vapour control as required behind internal cladding.

Underlayment for roof construction, where condensation and moisture control is required
Acts to keep sarking dry until roof is fixed
Acts as vapour control layer during serviceable life of roof
Can be laid either side up

Thermakraft Vapour Shield Moisture Control Barrier, if correctly installed, will meet the performance requirements of NZBC:

Clause B2, Durability (B2.3.1[a] 50 years), and B2.3.1 (b) 15 years
Clause E2, External Moisture

Thermakraft CoverTek 405 — Roof & Wall Underlay

Kingspan Thermakraft

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Thermakraft CoverTek 405 is a fire retardant self supporting synthetic roofing underlay for use under all claddings.

Thermakraft CoverTek 405 Fire Retardant Self-Supporting Roof Underlay has been appraised for use as a self-supporting roof underlay on buildings within the following scope:

the scope limitations of NZBC Acceptable Solutions E2/AS1, Paragraph 1.1 with regards to building height and floor plan area; and,
with masonry tile roof cladding; and,
with metal tile and profiled metal roof cladding; and,
situated in NZS 3604 Wind Zones up to, and including Extra High

Clause B2 Durability: Performance B2.3.1 (a), not less than 50 years, B2.3.1 (b), 15 years and B2.3.2. Thermakraft CoverTek 405 meets these requirements.

Clause E2 External Moisture: Performance E2.3.2. When used as part of the cladding system, Thermakraft CoverTek 405 will contribute to meeting this requirement.

Clause F2 Hazardous Building Materials: Performance F2.3.1. Thermakraft CoverTek 405 meets this requirement and will not present a health hazard to people.

Thermakraft CoverTek 405 Roof 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.

BRANZ Appraised

CodeMark

Thermakraft CoverTek 407 — Roof & Wall Underlay

Kingspan Thermakraft

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Thermakraft CoverTek 407 is a fire retardant self supporting synthetic building underlay for the use under all claddings.

Thermakraft CoverTek 407 Fire Retardant Self-Supporting Roof Underlay has been appraised for use as a self-supporting roof underlay on buildings within the following scope:

The scope limitations of NZBC Acceptable Solutions E2/AS1, Paragraph 1.1 with regards to building height and floor plan area; and,
With masonry tile roof cladding; and,
With metal tile and profiled metal roof cladding; and,
Situated in NZS 3604 Wind Zones up to, and including Extra High

Clause B2 Durability: Performance B2.3.1 (a), not less than 50 years, B2.3.1 (b), 15 years and B2.3.2. Thermakraft CoverTek 407 meets these requirements.

Clause E2 External Moisture: Performance E2.3.2. When used as part of the cladding system, Thermakraft CoverTek 407 will contribute to meeting this requirement.

Clause F2 Hazardous Building Materials: Performance F2.3.1. Thermakraft CoverTek 407 meets this requirement and will not present a health hazard to people.

Thermakraft CoverTek 407 Roof 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.

BRANZ Appraised

CodeMark

Thermakraft CoverTek 403 — Roof and Wall Underlay

Kingspan Thermakraft

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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.

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

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

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.

BRANZ Appraised

CodeMark

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