In the past few months numerous window problems are being brought to the attention of the Association. The problems can be generalised as follows:

• Building in of the window
• Waterproofing around the window frame
• Window sills

A badly installed window will always have inherent problems

Building In
Steel and wooden unglazed windows can be built into the wall as the brickwork or blockwork progresses. The window must be plumbed and wedges inserted under the frame to set the frame at the correct height (level). If the wall has a cavity the wall must be built solid for at least 114 mm at the window reveals. All fixing brackets must be built into the wall coursing as the walling progresses.
If the window is a pre-glazed unit an opening must be left by the bricklayer in the wall to the correct size. The easiest way to achieve this is to make up a frame template to the correct size for the bricklayer to build into the wall. The template should be a few millimetres bigger than the window frame to allow the frame to be fixed in the opening.

Waterproofing
The external and internal finishes specified will determine the manner in which the window is waterproofed. Plaster internally and externally must be applied to the reveals and window in a manner that meets the window frame at the designed intersection point. Sealant should be applied to the external and internal interface between plaster and window frame.

Window Sills
This is the most critical area in the window installation and the most neglected leading to water ingress as per the photo above. The damp proof course must be attached to the internal bottom transom of the window frame. The damp proof course must then be stepped down a course to the external wall face. When building a brick, tiled or plastered external sill there must always be a fall away from the window frame. The window sill must not cover or block any internal drainage channels or holes in the window frame or this could lead to rainwater draining internally.

By following the above good practices, the majority of window problems will not occur. Please remember a cheap and badly manufactured window will always have inherent problems and it does not matter how much time and effort is expended in the building in process, the window will fail.

R.H. Stembridge
Building Services Manager