Redway has designed a top and bottom Cavity Closer from extruded uPVC to be used in either a Drained Cavity wall or Ventilated Cavity wall situation.

  • A drained cavity wall is vented at the bottom only. Water is able to drain and limited (but often sufficient) air is able to enter the cavity to dry remaining moisture between wetting cycles.
    Products required: Redway Weatherboard Starter/Cavity Closer.

  • A ventilated cavity wall is vented at the top and bottom. As per the drained cavity, the bottom vent allows drainage and air entry. This method should be considered when drying is inhibited due to rapid wetting cycles or where walls are permanently shaded as they pose a higher risk of moisture build up and mould formation. An example detail of the ventilated cavity is illustrated on the right.
    Products required: Redway Weatherboard Starter/Cavity Closer and Redway Top Vent Closer

• All Weatherboard Starters/Cavity Closers and the Top Vent Closer are manufactured from rigid uPVC and are supplied in 2.7m lengths.
• All products are biologically and chemically resistant to treated materials such as treated timber. They will not rust nor react if in a salt zone.
• The uPVC compound is stabilised for UV protection as required by the NZBC.
• It is lightweight allowing for easy transportation and installation.



The New Zealand Building Code section E2/AS1 ( requires the use of a Cavity Closer as part of the proper construction of a drained cavity wall. The function of the Weatherboard Starter / Cavity Closer is to provide support and the correct starter angle for the first course of weatherboard, prevent vermin intrusion, and to promote weather-tightness by allowing drainage and air ventilation to dry the cavity should moisture breach the external cladding. The Redway range of uPVC Weatherboard Starters have been designed to provide the ideal solution for architects, builders and installers to meet these requirements. Redway Weatherboard Starters / Cavity Closers are available at all leading building merchants nationwide.



• A preformed sloped edge to provide the correct angle for the first course of weatherboard.

• The angled edge creates a tight and consistent seal with the weatherboard to prevent water from wicking up from the ground or from a sprinkler head. The tight seal also prevents vermin intrusion into the cavity. *Designers/builders must use the correct size weatherboard starter / cavity closer to achieve this seal and comply with the NZ Building Code.

• Ventilation holes to allow moisture drainage from the cavity. Bottom ventilation permits a minimum of 1000mm2 per metre length of air into the cavity as specified by E2/AS1. For enhanced drying capacity, use with the Top Vent Closer.

• Strong product thickness to provide weatherboard support.

• Available in 4 sizes - 25mm, 30mm, 33mm and 35mm.




  • Extruded uPVC strip
  • Fits weatherboard or flat panel up to 20mm thick
  • Front ventilation holes that promote air flow and allow air and moisture to exit the cavity
  • Raised back edge to prevent wind-blown rain or hose water from saturating the cavity
  • A positive slope to direct any water towards the building exterior
  • Flat top edge to butt against the soffit for a tight seal


* Creates an air path from the bottom cavity closer that will increase the rate of drying
* Allows air and moisture to escape reducing the risk of deterioration
* Easy to install
* uPVC material is biologically and chemically resistant to treated materials, nor will it rust or react if in a salt zone
* Cut to the exact size on the building site
* Lightweight for easy transportaion and installation


Material Rigid uPVC
Length 2.7m
Colour White
UV stabalised Yes
Nail holes No


When installing weatherboards without a cavity, fix the Redway Cant Strip (Weatherboard Starter) before the first course of weatherboard to achieve the correct angle and provide support for the weatherboard. This method saves time, money and materials when compared to ripping a piece of weatherboard as a starter.

The Cant Strip is manufactured from the same durable uPVC compound as other Redway flashings.


The 40mm Weatherboard Jamb provides weathertightness protection to the vertical junction between brick and weatherboards - a common detail on many new builds.