Window Installation & Flashing by Paarhammer

There may also be specific requirements for the airtightness of the building envelope for energy efficiency. Different construction methods of the building, e.g. solid construction, lightweight construction, timber framing, etc. require different approaches to window and door installation.

One of the most important parts of window installation is flashing to protect against water ingress which can result in water damage, rot and mould. While windows are tested for water ingress and wind load, very little can be done by the window supplier to prepare windows to be installed in any possible building envelope. Flashing requirements need to consider variations in climate, geographic conditions, exposure of the window to the elements, the type of construction and other design requirements.

Performance Requirements 

The Building Code of Australia (BCA) under the National Construction Code (NCC) provides performance requirements which are covered under AS2047 and AS1288. The Australian Glass and Windows Association (AGWA) provides guides to ‘Residential Window Installation’ and to ‘Window and Door Fixing’. The below information is from the AGWA Window Installation Guide:

There are three types of flashing: Sill, Jamb and Head. Flashing must be installed from bottom to top, in the following order, so that each layer overlaps the one below:

1. Sill flashing

2. Jamb Flashing

3. Head Flashing

The sarking above the window overlaps the head flashing. Overlap is vital to ensure that, at each transition, water is directed onto the element below. Drainage must be provided below the window or door, so that any water captured has the ability to escape to the outside of the wall.