Low Pitch Roofing Ventilation

There are plenty of articles published about why roof space ventilation is crucial to minimise moisture related problems. It is especially true with low pitch roofs, where a smaller roof space means there is a higher chance of mould growth and interstitial condensation if no airflow exists.

Venting the roof space is an important step in avoiding excessive moisture and mould growth. Designers, specifiers, builders and roofers have been looking for easy to use guidance on how to effectively ventilate roof spaces.

DriSpace Systems are ventilation guidelines that provide solutions to minimise the risk of condensation. These systems include roof underlays, wall underlays and Vent NZ products. The systems include the specifications to meet various performance requirements.

DriStud roof and wall underlays offer high vapour permeability (vapour resistance less than 0.5MNs/g) and Vent NZ products introduce air flow. DriSpace have specific solutions to ventilate low pitch roofs as detailed in the tables below:

Skillion roof pitch 3° or above — steel longrun roofing

Specification code	DriSpace specification	Underlay	Vent components	Fixing & Accessories
DS-FRU3803-SLV	Steel longrun skillion roof Roof pitch: 3° or above Ventilated with fire retardant underlay	FRU38	G2500N VB20 RV10P or RV10DT	Galvanised or s/s staples, clouts or purlin screws self tapper, DriStud Joining Tape. Wire netting or plastic strapping.
DS-RU2403-SLV	Steel longrun skillion roof Roof pitch: 3 ° or above Ventilated with non-fire retardant underlay	RU24	G2500N VB20 RV10P or RV10DT	Galvanised or s/s staples, clouts or purlin screws self tapper, DriStud Joining Tape. Wire netting or plastic strapping.

*75mm galvanised hexagonal wire netting to AS/NZS 4534, builders tape or other strong durable materials for roof pitch less than 10°.

Trussed roof pitch 3° to <15°

Specification code	DriSpace specification	Underlay	Vent components	Fixing & Accessories
DS-FRU3803-SLV	Steel longrun trussed roof Roof pitch: 3° to <15° Ventilated with fire retardant underlay	FRU38	G2500N G502	Galvanised or s/s staples, clouts or purlin screws or self tapper. Wire netting or plastic strapping.
DS-RU2403-SLV	Steel longrun trussed roof Roof pitch: 3 ° to <15° Ventilated with non-fire retardant underlay	RU24	G2500N G502	Galvanised or s/s staples, clouts or purlin screws or self tapper. Wire netting or plastic strapping.

Roof Ventilation Facts:

The more airtight any space is the more likely that any moisture that reaches it will accumulate.
New Zealand houses have become more airtight and there is evidence that this trend extends to roof spaces as well. Without proper management of indoor moisture in buildings that are more airtight, moisture and pollutants can build up and mould growth can become a significant issue.
In some New Zealand homes, vapour barriers have been used to limit entry of moist air into the ceiling space, but control of air movement into the cavity and removal of damp air by ventilation is a more practical approach.
The roof space is generally inaccessible, with little natural ventilation and a small roof space can further accelerate problems with moisture. Skillion roofs need carefully designed and installed ventilation to reduce the risk of moisture-related problems.

Please visit www.drispace.co.nz to download the latest DriSpace Systems literature.

DriStud RU24 — Synthetic Self Support Roof Underlay

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DriStud RU24 is non-fire retardant self-supporting black faced synthetic roofing underlay.

Intended for use on new and existing buildings in wind zones up to and including ‘Extra High’, as defined in NZS 3604:2011.
DriStud RU24 is designed to be used as a replacement for self-supporting kraft paper roof underlay. It can be installed over both timber and steel framing to ensure a dry roof cavity.
DriStud roofing underlays must be installed with all writing and imagery facing out and with as minimal a number of overlaps as possible.
Where overlaps are unavoidable a lap of 150mm minimum must be used.
DriStud RU24 must not span more than 1.2 m between adjacent supports.
DriStud roofing underlays must be installed as described in paragraph 8.1.5, E2/AS1.

If designed, installed and maintained in accordance with the conditions of the CodeMark Certificate, DriStud RU 24 roofing underlay will comply with the following clauses of the New Zealand Building Code:

B1 Structure: B1.3.1, B1.3.2. With respect to B1.3.3, (a), (h).
B2 Durability: B2.3.1 (a), B2.3.2 (b).
F2 Hazardous Building Materials: F2.3.1

Will contribute to compliance with;

E2 External Moisture: E2.3.1, E2.3.2, E2.3.7 (a), (b), (c).

CodeMark

DriStud FRU38 — Fire Retardant Synthetic Self-Support Roof Underlay

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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

CodeMark

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