WINDOW REPAIR Features
Repairing Historic Windows
Julian Davies gives some
practical guidance on window repair in listed blocks
use higher-quality timber in the eighteenth and nineteenth centuries. That's why sash windows from that period often continue to function extremely well. In the post war period, however, it became more common to use plantation-grown timber rather than natural timber, and consequently many timber windows dating from the 1960s and 70s now have to be replaced.
Before and after (top right): repairs to timber sash windows is best done on site
In the last issue of Flat Living, I looked at the issues involved in replacing windows in listed residential blocks. This follow-up
article gives some practical guidance on repairing the types of windows that are commonly found in listed buildings, where replacement may not be an option.
New guidance from Historic England, Traditional Windows: their care, repair and upgrading, is not to replace windows in listed buildings at all, but to repair existing windows instead. Where there are proposals to replace windows, the local planning authority may require robust evidence that the existing windows are beyond repair in practical terms – it is not enough just to say
Issue 21
it would be too expensive. There are many advantages to this approach, most obviously in terms of maintaining a building's character and avoiding the loss of historic fabric. But there are often practical benefits too, since historic windows are often of very high quality and with a little work can be made to serve their purpose for many more decades. The Historic England document is an invaluable resource, which I have drawn on in summarising the issues involved in repair.
Repairing timber windows It's perfectly true that things in the past were built to last, so the first reason for repairing rather than replacing historic timber windows is that builders tended to
In the case of older timber windows, even when they are in need of attention, rather than replacing a whole window frame, it is often possible to replace or reinforce only those parts of the window that are particularly damaged. Despite the perception that such repairs are only a short-term 'band aid' solution, done properly they can extend the lifetime of a window for many years.
Repairs are best done on-site; if sash windows and casements are removed for repair, it is important first to photograph them in position for the record. Rotten wood in the frame should then be cut out and replaced by splicing or scarfing-in timber inserts made from good-quality wood similar to the original timber in order to replicate the original profile. The grain of the timber should also be oriented to match the parent in order to reduce the risk of differential movement leading to splitting.
Of course, if the damage has been caused by moisture penetration, it is vital to deal with the causes before completing the repairs. One common problem is open joints that let moisture in. These can be re-secured by cramping, glueing, re-wedging and pinning,
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