Fletcher Insulation has developed two condensation management solutions using Sisalation® Vapawrap® Vapour Permeable Metal Roof sarking to manage condensation in standard pitched roof spaces for the comfort of occupants in temperate and cold climates. (The solutions are not suitable for buildings in hot and humid climates such as Climate Zone 1).
- Solution 1: Sisalation® Vapawrap® Vapour Permeable Metal Roof sarking installed under batten.
- Solution 2: Sisalation® Vapawrap® Vapour Permeable Metal Roof sarking installed under drainage batten.
Both solutions are based on recommended installation methods described in the Tasmanian Designers’ Guide (referenced in the ABCB’s Condensation in buildings Handbook 2019).
Sisalation® Vapawrap® Vapour Permeable Metal Roof sarking is a synthetic sarking specifically designed for use under metal roof cladding materials. It provides a lightweight, flexible water barrier and water vapour permeable membrane that can be used underneath metal roofing.
By installing Sisalation® Vapawrap® Vapour Permeable Metal Roof sarking under battens or under drainage battens, thermal bridging is minimised. With the presence of ventilation in the sarking zone and the roof space, these conditions combined will minimise condensation in the roof space.
Sisalation® Vapawrap® Vapour Permeable Metal Roof sarking can be installed prior to the battens being installed, an extra counter batten can also be installed on top of the batten for better ventilation or wider air gap if desired. Alternatively, one or two-layer drainage battens can be added before the roof cladding is installed.
In the unlikelihood of condensation occurring beneath the metal roof cladding, these solutions can:
- provide a venting pathway above and below the membrane to allow moisture to escape from the roof system and protect the roof structure
- allow condensates to drain into the gutter
- function as a water barrier, preventing water from dripping through the membrane.
Fletcher Insulation recommends suitably designed natural or mechanical ventilation for the roofing system and an increase in ceiling insulation to compensate for any loss of thermal and acoustic insulation.
Fletcher Insulation Drainage Batten
Fletcher Insulation’s drainage batten is a flame retardant twin wall channel designed to facilitate air and vapour movement and create a pathway for drainage between the Sisalation® Vapawrap® Vapour Permeable Metal Roof sarking and the metal roof cladding. Constructed from high impact copolymer polypropylene for enhanced impact resistance, it is extremely tough and durable.
The drainage batten is recommended for installation over Sisalation® Vapawrap® Vapour Permeable Metal Roof sarking when using on residential metal roofs with a standard pitch roof. It provides an independent separated space between the metal cladding and the Sisalation® Vapawrap® Vapour Permeable Metal Roof sarking, effectively reducing the risk of condensation by allowing an unobstructed drying path for condensate liquid to drain away into the gutter.
Drainage batten benefits
- Provides drainage and a ventilation pathway under metal roofing.
- Reduces the risk of ponding on sarking behind roof battens and at eaves.
- Facilitates sarking to be installed without contacting the roof cladding, consequently, reducing the risk of condensation forming under the roof sarking.
- Can be used where roofing battens have already been laid on a roof permitting quicker install of system and compliance with building standards.
- Reduces conductive heat transfer between the roof and wall cladding and the building structure.
- Will not readily melt or spread flame in the event of a fire.
