Metal Cathedral Roof >10°
Primary insulation layer parallel to roof plane (Cathedral)
All VENT Systems technical advice presents BEYOND COMPLIANCE of the National Construction Code 2025 Vol 1: F8D5 & F8D6 / ABCB Housing Provisions Standard 10.8.3 to ensure mitigation of the risks associated with internal moisture in the roof cavity. BEYOND COMPLIANCE solutions go above and beyond the requirements of the NCC 2025, addressing critical areas such as preventing dew point transference, enabling Class 4 vapour permeable membranes to function effectively, and ensuring unimpeded airflow past insulation. These measures are essential for maintaining optimal conditions within the roof space and minimising the potential for moisture-related issues.
VENT Systems offers a range of solutions compliant with AS3959, AS4200 as well as NCC 2025.
Ventilation of a roof space with the primary insulation layer parallel to the roof plane (Cathedral):
For roofs any degree <10m² – 7,000mm²/lm at Low Level and 5,000mm² /lm at High Level.
For roofs any degree >10m² – 20,000mm²/lm at Low Level and 5,000mm² /lm at High Level.
FOR COMPLIANCE:
Application for Roofs any degree <10m²
Low level: Requires 7,000mm² /lm
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- Our G750N Over Fascia Vent 7.5mm guarantees a calculated airflow of 7,500mm²/lm, ensuring compliance effortlessly at Eaves or Box Gutters.
High Level; Application at Abutment, Barge or Parapet
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- Pitches 10-15° – Our RV10AP-HALF Ridge Vent guarantees a calculated airflow >7,000mm²/lm and/or our BV10 High Level BAL Vent guarantees a calculated airflow of >10,000mm²/LM (5,000mm²/lm p/side), both ensuring compliance effortlessly at the high level.
- Pitches >15° – Our BV10 High Level BAL Vent guarantees a calculated airflow of >10,000mm²/LM (5,000mm²/lm p/side), both ensuring compliance effortlessly at the high level.
Application for Roofs any degree >10m²
Low level: Requires 20,000mm² /lm
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- Our G2500N Over Fascia Vent 25mm guarantees a calculated airflow of 25,000mm²/lm, ensuring compliance effortlessly at Eaves or Box Gutters.
High Level; Application at Abutment, Barge or Parapet
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- Pitches 10-15° – Our RV10AP-HALF Ridge Vent guarantees a calculated airflow >7,000mm²/lm and/or our BV10 High Level BAL Vent guarantees a calculated airflow of >10,000mm²/LM (5,000mm²/lm p/side), both ensuring compliance effortlessly at the high level.
- Pitches >15° – Our BV10 High Level BAL Vent guarantees a calculated airflow of >10,000mm²/LM (5,000mm²/lm p/side), both ensuring compliance effortlessly at the high level.
ABOVE COMPLIANCE:
The VB20 Ventilation & Drainage Batten 20mm ensures a continuous air gap & unimpeded airflow through the roof cavity, above the roof battens,
The VB10 Ventilation & Drainage Batten 10mm prevents dew point transference by creating a 10mm ventilation & Drainage cavity between the metal roof and the Class 4 vapor permeable membrane.
For bespoke or complex designs there are numerous alternatives that can be considered. Contact our specialist team for further assistance
DISCLAIMER: Product combinations specified within Vent Systems Pty Ltd (ACN 682 448 997) (Vent Systems) technical documentation are designed to mitigate the risk of moisture accumulation and condensation when installed correctly. Unless otherwise indicated, Vent Systems’ individual products or product combinations generally comply with relevant requirements of the Australian Standards and National Construction Code (NCC). However, compliance with NCC minimum requirements alone may not provide adequate moisture and condensation management per sae. Vent Systems can provide professional and tailored advice as to the suitability, specification and installation of ventilation systems. Except to the extent that we have provided tailored advice, to the fullest extent permitted by law, Vent Systems accepts no liability for losses, damages or defects arising from the specification, installation or performance of its products, and does not guarantee any condensation control, moisture mitigation or overall building performance.
G750N – Over Fascia Vent
The VENT Over Fascia Vent – G750N is the most practical and cost-efficient way to ventilate the eaves on traditional roofs pitched at 15 degrees or more, delivering 7,500mm²/lm of free airflow. Paired with the VB20 Ventilation & Drainage Batten it reaches 22,000mm²/lm, which is enough to meet NCC airflow requirements for pitches under 15 degrees. It is easy to install, sits discreetly hidden behind the spouting, suits both timber and metal fascias, and works with no moving parts or energy use.
VB20 – Ventilated Batten
The VENT Roof Cavity Batten – VB20 is a 20mm polypropylene ventilation and drainage batten that moves 14,500mm²/lm of free airflow through a cathedral roof, between the roofing underlay and the roof battens or purlins. It holds these tight roof cavities open so insulation cannot block them, and works year round with no moving parts or energy use. Fitted behind the fascia and paired with the G750N Over Fascia Vent it reaches 22,000mm²/lm, meeting NCC requirements for pitches under 15 degrees.
G1275 – Eaves Comb Filler
The Eaves Comb Filler G1275 uses flexible fingers that adjust to fill the gaps left by profiled concrete tiles or metal roof cladding, keeping birds and large insects out of the roof while air still flows freely into the cavity. It is a cost-effective replacement for purpose-made fillers that block airflow above the underlay and trap moisture from leaks or dew point. Supplied in 1m lengths, it fits over VENT Systems Over Fascia Vents or directly to timber or metal fascias. For BAL-0 zones only.
G2500N – Over Fascia Vent
The VENT Over Fascia Vent – G2500N is the simplest, most cost-efficient way to ventilate the eaves on cathedral and traditional roofs pitched under 15 degrees. Delivering 25,000mm²/lm of free airflow, it clears hot air from the roof void and manages condensation year round with no moving parts or energy use, while meeting NCC DTS requirements. It is easy to install, sits completely hidden behind the gutter, suits timber and metal fascias, and is the only solution for ventilating a build with no eaves.
G502 – Roll Panel Vent
The VENT Systems Roll Panel Vent G502, also known as an Eaves Baffle or Insulation Guard, holds a 25mm air gap between the insulation and the roofing underlay so air flows freely through the eaves into the roof cavity. Insulation batts can sit full depth above the wall plate with no gaps, cold spots or heel height adjustments, protecting the Energy Star rating that poor eaves insulation erodes. Suitable for concrete and metal roofs, it guarantees compliance with NCC 2022 Vol 1 F8D5 and ABCB Standard 10.8.3.
VB10 – Ventilated Batten
The Ventilation & Drainage Batten 10mm VB10 is a polypropylene batten that creates a 10mm ventilation and drainage cavity between the roofing underlay and the Colorbond cladding, delivering 7,250mm²/lm of free airflow. That separation prevents dew point transferring from the roof sheet to the membrane, and moves hot air into the roof void with no moving parts or energy use. It meets NCC DTS requirements and works well behind lightweight wall claddings or in place of larger over fascia vents.
Ridge Vent
The VENT Ridge Vent – RV10 clears warm, moist air from the highest point of the roof void, using the natural convection of rising warm air and the negative pressure created by wind passing over the roof. Delivering 7,000mm²/lm of free airflow per side, it works year round with no moving parts or energy use. Its adhesive, flexible aluminium flashing forms to the roofing profile to prevent water ingress on any roof pitch, with RV10P suiting cladding profiles under 34mm through depth and RV10DT covering 34mm to 38mm. As a high level vent it performs best paired with low level intake, such as Over Fascia or eaves ventilation.
