A Three Step Solution for Ventilating Skillion Roo

TCL Hunt Building Products offer a system solution to minimise condensation in the roof cavity and keep the building breathing. For skillion roofs with limited space in the roof cavity, DriStud recognises there is a much higher risk of moisture accumulation within the roof space. Applying Vent systems and high vapour-permeable underlays will improve durability and mitigate the risk of internal moisture build-up and associated issues caused by internal moisture. Based on international best practice, using the right passive ventilation system ensures the roof space and insulation remains dry, preventing the occurrence of dampness, mould and rot.

Roof underlays

DriStud Roof Underlays are designed to manage and minimise the risk of condensation with their high vapour permeability (average 0.2MNs/g of vapour resistance, ASTM E96 Procedure B) which allows moist air to pass through the underlay.

DriStud Roof Underlays have been tested to meet the following requirements:

Property	Test Method	Requirement	Results
Water Vapour Resistance	ASTM E96 Procedure B	≤ 7MN s/g	Pass
Absorbency	AS/NZS 4201: Part 6	≥ 150 g/m²	Pass: 225 g/m²
Air Resistance	BS ISO 5636-5:2003	≥ 0.1 MN s/m3	23.3 MN s/m³
Water Resistance	AS/NZS 4201.4:1994	≥ 100mm H2O	Pass
Flammability	AS 1530.2:1993	FR Index ≤ 5	FR Index 3
Resistance to UV Exposure	ASTM G154		20 days
Mechanical	ASTM D882	Tensile Strength	MD: 6.88 KN/m CD: 5.84 KN/m
Edge Tear Resistance	TAPPI T470	Edge tear strength	MD: 351 N CD: 302 N

Passive Ventilation:

Vent NZ has developed two passive ventilation systems specifically tailored to the different requirements of pitched skillion roofs and mono-pitched skillion roofs.

For a pitched skillion roof of any degree pitch, Vent recommends installing a three product combination.  Firstly, the Vent Over Fascia Vent – G2500N is fitted to the top of the fascia to allow calculated airflow of 25,000mm² per linear metre into the roof cavity. Then VB20, ventilated battens are applied to each purlin, ensuring unimpeded airflow through the centre of the roof cavity. Then Ridge Vents are installed to create negative pressure to draw consistent and constant airflow through the roof and allow warm, moist air to escape the roof cavity.

 Vapour check layer:

Where there is a higher risk of condensation, DriStud recommends installing ProctorPassive SmartVap 100 — a barrier and variable vapour diffusion resistance retarder.

ProctorPassive SmartVap 100 will form an airtight layer, improving the efficacy of ventilation systems and thermal efficiency of the building enclosure. The effective management of air and vapour passage through wall, ceiling and floor assemblies can help protect the building fabric and insulation from condensation and related problems such as mould, timber rot, corrosion and loss of thermal resistance.

Please visit the DriStud website or call on 021 935 555 if you would like a copy of the DriStud Roof Ventilation Design Guide.

ProctorPassive SmartVap

DriSpace

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ProctorPassive SmartVap is a two layer AS/NZS 4200.1 compliant light duty air barrier and variable vapour diffusion resistance retarder.

Designed for effective management of air and vapour passage through wall, ceiling and floor assemblies
Can help protect the building fabric and insulation from condensation and related problems such as mould, timber rot, corrosion and loss of thermal resistance
When installed as a continuous layer, SmartVap will form an air tight layer, improving the efficacy of ventilation systems and thermal efficiency of the building enclosure

Two layer AS/NZS 4200.1 compliant

DriStud FRU38 — Fire Retardant Synthetic Self-Support Roof Underlay

DriSpace

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DriStud FRU38 is a white synthetic tri-laminate roofing underlay that is water resistant, vapour permeable and fire retardant.

DriStud FRU38 is intended for use on buildings designed in accordance with NZS 3604:2011 paragraph 1.1 and in wind zones up to and including 'Extra High'.
DriStud FRU38 is designed to be used as a replacement for standard kraft paper roof underlay.
It can be installed over both timber and steel framing to ensure a dry roof cavity.
DriStud FRU38 can be used under: masonry tiles, metal tiles, profiled metal roof claddings.

Where CodeMark is to be relied upon, then all conditions of that certificate must be met. These are:

Must be installed in accordance with the DriStud FRU38 Installation Guide Rev 1.
DriStud FRU 38 may be installed over timber and steel roof framing.
The certificate covers the use of DriStud FRU 38 under: masonry tiles, terracotta tiles, metal tiles, profiled metal claddings, slate and composite panels.
DriStud FRU38 can span up to 1200mm between adjacent supports. Where the span exceeds 1200mm a corrosion resistant mesh or alternative i.e. plastic strapping must be used.

When specified and installed in accordance with the requirements of the Installation Guide, DriStud FRU 36 roofing underlay will comply with the following provisions of the NZ Building Code:

Clause B1 Structure: B1.3.1, B1.3.2, B1.3.3 (a, h)
Clause B2 Durability: B2.3.1(a), B2.3.2(b) (15 years)
Clause C Protection from Fire: C3.4(c)
Clause F2 Hazardous Building Materials: F2.3.1

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