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Fitting a window frame can be quite a task especially if you are unexperienced. Why learn from your mistakes? Follow these step by step instructions and get it right first time
Replacing most window frame is straight forward, while others can be challenging. Much depends on the window type, and how it was originally fitted.
Before proceeding with any work, you must first satisfy yourself that there is a lintel in place, so that when the old frame is removed the brickwork above is safely supported.
In older properties the window was usually fitted from the inside, behind and up to the outer wall of the cavity wall brickwork sitting onto a decorative shaped stone sill, so that most of the window frame was hidden. The outer brickwork would have a decorative lintel, or arched brickwork for support.
The inner wall of the cavity usually have a timber lintel, and the internal finish would be timber lined, finished with architraves. The Sliding Sash Window is a good example of this type of installation, and is shown in cross section plan view (above right).
When replacing a Sliding Sash Window with a modern frame, thought must be given as to where the new frame is to be located in relation to the brickwork. This will either be as the original set behind the outer wall, or fitted between the outer wall of the cavity wall, set back about 25mm from the face. No matter which option taken, the work can get quite extensive, even if the new frame is fitted as the original.This is due to the extra width of the box section of the sash window for carrying the weights. The modern replacement frame requires less space because it doesn't have to accommodate weights in its design, and this results in a dramatic difference in frame width when compared. In addition to this, the depth of the new frame is also smaller as the openers in a casement frame are all fitted to a single rebate, where the sashes of the Box Sash window fit into two channels one in front of the other. Despite this, fitting as the original is the easiest option to take, as fitting the frame to the outer wall will mean removing the stone sill, and making good the opening with matching brickwork. Internally too, extensive making-good can also be required with both options.
The drawing (above left) shows a typical arrangment of the brickwork when the old Box Sash window has been removed.
In this case the cavity has been closed, and has a vertical DPC to stop the moisture from travelling across the brickwork closer.
