A Guide to Period and Modern Windows: Maintenance, Pitfalls, and Replacement Costs

Released On 31st Jan 2026

Unless you are buying a house three or four hundred years old, you are unlikely to have to deal with extremely old, hinged, single-glazed timber casements or the other window dating from that period, namely casements windows incorporating leaded lights where strips of lead provide a framework into which the original glass was set.  Such windows require specialist maintenance if they have significantly deteriorated over time needing to be preserved to retain the historicity of the property and their retention likely being a legal requirement under Listed Building legislation.

Much more likely to be encountered, in terms of period windows, is the standard Victorian window, known generally as a double-hung timber sash window. In this window form, casements run up and down in a box frame, usually set into recesses in the brickwork on either side of the windows.  The top and bottom casements move vertically on flax cords, with the weight of the casements being balanced by metal weights, which are concealed within the box frame.  These original windows, being only single-glazed, have poor thermal insulation qualities but, where original, they form an integral part of the historic appeal of the property and would generally be regarded as worth retaining, despite their thermal limitations.  However, these types of windows can suffer from a number of defects, which have developed over time, some of which can be summarised as follows:

1. Individual glass panes can be cracked and, if there is a desire to replace original glass, which has wavy lines and bubbles within it, known as drawn glass, then this can be extremely expensive to source for a glazier to fit.
2. Often, these windows have been painted shut in the past, often due to their non-functioning and sometimes they may not operate satisfactorily, due to distortions in the timber over time that have caused them to fit too tightly into the frames, therefore needing easing and adjusting.  Such work may require the removal of the middle beads, known as parting beads, or the internal restraining perimeter timbers, known as staff beads, in order to get them moving again.
3. Sometimes, windows do move within the frames, but in a random, haphazard and juddering fashion, again needing easing and adjusting, in order for them to move freely once more.
4. On other occasions, often the weights do not balance the casements correctly and, therefore, the casements simply drop down when opened, being heavier than the weights that should counterbalance them and hold them in position.
5. However, of most concern would generally be the lack of proper maintenance over the last hundred years to many of these windows, resulting in spot areas of timber decay to the frames and the casements themselves.  Sometimes they can be repaired with modern joinery repair compounds, but in some instances the decay will be so severe that the whole window needs to be replaced. 

Many average carpenters no longer have the skills necessary to refurbish these windows so that they function correctly and, therefore, it may be difficult to find someone with the appropriate skills to put them back in first class working order.

This type of window was almost universal during the Victorian period but was largely superseded in the 1960s and 1970s by two further types of window:

1. Single-glazed, metal-framed crittall windows, which have no thermal insulation properties whatsoever, tend to stream with condensation during the winter months, even with adequate internal heating, and also can suffer from corrosion, particularly behind the putty, where water is held and causes the ferrous metal to rust.
2. Also from this period, single-glazed, side-hung timber casements became the window norm

It is becoming rare to find either of these two types of windows still in situ, the majority now having been replaced with modern, purpose-made, double-glazed equivalents.

Since the 1980s, most replacement windows have been double glazed, either in traditional timber or, increasingly, of a UPVC type, which are maintenance-free, given the nature of the material out of which they are formed, but with significant issues now being highlighted in respect of their lack of green credentials.

Many of these original first generation double-glazed windows from the 1960s, 70s and 80s were of inherently poor quality and have now reached the point of needing either significant repair or replacement, due to a lack of quality in the first place and poor maintenance attention since then.

They also tend to have a very thin double-glazing gap, which means that they are nowhere near as thermally efficient as modern double-glazed windows, which have a much wider gap.

Such poor quality units can develop a failure in the double-glazing arrangement, where moisture enters the perimeter of the seals that have failed, resulting in condensing water vapour within the double-glazing gap.  Such windows cannot be repaired and, as a minimum, the glazed units will need to be taken out and replaced.  However, if one unit has failed, it is likely that, over time, further units will fail and it may be seen as an unnecessary aggravation to have to replace the units on a periodic basis, rather than replace them with new windows of better quality, which not only have the wider double-glazing gap but also tends not to have a problem with hermetic seal failure in the same way.

There was a fad some ten to twenty years ago to use what are known as ‘tilt and turn’ windows, which, although no longer widely used, can still be found in some isolated modern constructions.  The tilt and turn mechanisms mean that they can be opened traditionally from the side, when the handle is turned 90° and then from the top when the handle is turned 180°.  Sometimes, these mechanisms fail or don’t function efficiently, with the windows either not opening correctly or catching on the frames in the opening process.

One final area of particular concern in respect of double-glazed windows, be they metal, timber or PVC, is where they have been installed in such a way as to utilise the original window frames from the windows that they are replacing.  To try and set new windows into old frames in the misguided belief that in some way the original frames can be retained, although they would likely have been suffering from as much timber decay as the casements that are being replaced, is fundamentally flawed.  

We have come across numerous occasions where modern windows, which of themselves are still in satisfactory condition, have been completely compromised by the retained frames into which they are set having decayed, often to the point where the rot has passed through the back of the frame, making repair access extremely difficult.  It would be almost impossible to find any carpenter to come to site to take out a replacement window, remove the original frame, build a new timber frame in and then reset the retained window.  The cost would be prohibitive and, whilst windows may not be seen as a high-ticket item in terms of potential repair costs when moving into a new property, suddenly finding that all the frames that were retained are suffering from a degree of timber decay, with all of the windows therefore likely to need full replacement, can easily produce an unexpected cost of repair of, say, between £10,000 - 20,000.00, depending on the size of the property and the quality of the windows, but providing a nasty shock if their poor condition had not been fully appreciated at the time of purchase.