Why Preserve historic windows?

windows of interest in southampton

There is pressure to replace wooden windows with PVC-u this has come about partly by plastic window industry which has heavily invested in marketing, with the often optimistic claim made to fit replacements  in one day to a whole property, and the promise of a seamless experience with out the need too bring in other trades, may seem an attractive one.

The term ‘worn out’ is often used by the salesman to describe the condition of original windows rather than an actual assessment being made and the whole idea of replacement is driven by a culture of fashion  and upgrades. This can result in inappropriate adaptations particularly in a conservation area as PVC-u cannot match traditional wooden windows.

Sections and proportions of historic joinery. Historic joinery would be represented in most  pre 1970s dwellings.

Windows are the eyes of a building and profoundly effect its appearance and in addition represent the artistic social and economic development of an area and also reflected in many cases the status of a dwelling and its occupants.

Due to the high quality of timber used in the original, old windows can have long lives, often I come across windows that are 100,150 or even 200 years old and are usually economically repairable. It would take many years if ever that you would get back savings on heating having PVC-u fitted, and energy offsets making PVC-u windows in the first place are enormous. Estate agents often refer to the fact that replacement of historic windows and doors to PVC-u threaten the value of your property particularly in conversation areas.

Types of glass found in historic windows

Broad Glass.

A method used widely in the 12 and 13th century found mainly in churches and cathedrals made by blowing a bubble of molten glass swung to create a tube this was then laid and flattened with  the ends cut. Once cool the tube was cut into small rectangular lengths of sheet glass.

Crown glass.

Molten glass was spun producing a disc examples exist from the 14th and 15th century but when the tax on glass by weight ended cylinder glass became popular. Crown glass was made up to the 20th century.

Cylinder glass.

A type of Broad glass but with advanced methods employed it became possible to make larger tubes, this method became popular up to the beginning of the 20th century and many examples exist in private dwellings of that period.

Polished plate glass.

Developed in France glass was laid on a polish table and ground and polished to produce a clear sheet as mechanisation was being introduced glass for the first time was becoming less expensive this method was employed between the 18th and 19th century.

Drawn glass.

Often referred to as flat sheet. Molten glass was drawn between a die a bit like the old fashioned mangle used to wring clothes producing a flat continuous sheet.

This became the industry standard many examples still exist. It can be identified by the mottled effect and bubbles unless your property was bomb damaged during the war years or through some other breakage  you probably have this type.  


Invented in 1950 molten glass is allowed to flow over molten tin it results in a completely flat and featureless product of exact thickness and characteristics throughout.  


Development in glass production from around the 16th century  was reflected in the appearance of windows. Pieces of broad glass were laid in lead quarries but buildings still had often only one window that opened whilst servant quarters and low status rooms were not glazed, a waxed cloth was used along with shutters to keep the night out.

It was not until the 17th century that casement windows with sliding sashes became fashionable and with the onset of larger sheets of glass it became possible to fit these into rebates within the frame and glazing bars with metal sprigs were employed to keep the glass in place and finished in putty to keep the weather out.

The earliest sliding sashes had the top sash fixed. The lower one slid upwards and was held in place with pegs.

Not commonly known is that  the double hung sash window that you see today was a British invention although the French like to think it was theirs! As they were the ones who came up with the bottom sliding sash.  Using counter weights both sashes could be opened enabling a system of ventilation to be employed. The earliest example dates from 1701 and by 1750 most new development employed this system.

Many variations of this theme were employed and being British ridden by class the better off had swept heads (curved) , bowed, and elaborate decorative glazing bars. This can often be seen in fan lights above main entrance doors which also were becoming popular and stamped on the world a message of status.

Both Crown and cylinder glass was used during this period.

Glazing bars also were going through a development from large chunky Oak members to slender ovolo and quarter circle mouldings this in part was due to the import for the first time of cheaper softwood mainly Scandinavian pine. By the 19th century glazing bars were down to 12mm wide with pointed gothic mouldings.

With the introduction of cheaper plate glass from about 1830 which was stronger and available in larger pieces the need for glazing bars was reduced allowing for larger areas of uninterrupted views to the outside.

Thermal upgrading windows

Energy efficiency for reasons of economy, comfort and, reducing carbon emissions are a major priority. Economy because we all want to save money and there is only one direction that fuel bills go. Comfort – who would want to live in a cold home with draughts which adds not only to the economy argument but also the emission part of the trilogy.

Carbon emissions in my view is the big one, an extra jumper or thicker curtains will mitigate to a certain extent the issue of comfort but carbon emissions affects us all.

The amount of energy required to manufacture PVC-u windows and doors will take many years before it is off set buy savings in reduced emissions achieved by installing them if ever and there is to my knowledge no recycling of these units which are now becoming a landfill problem.

A whole building approach by that I mean looking at all possible ‘heat sinks’ can help in reducing waste.

The heat loss from windows can vary considerably it depends on the size of the window in ratio to the external wall. Heat can be lost through poor installation and ill-fitting sashes, conduction through the glass and from radiation through surfaces.

Retro fitting draughts excluders and brush seals outlined else where on this site can dramatically reduce draughts, bear in mind draughts can move in two directions into the room and out of the room.  Research has shown that fitting these simple seals can have an 80% impact reduction. Another benefit also is the acoustic proofing that results from these seals.

On the subject of research, thick curtains the sort my mother used to hang at the beginning of every winter- they were made from a second hand stage curtain which once hung at the old Atherly Cinema in Shirley can have the same thermal impact as double glazing. Not that we all have second hand stage curtains but you hopefully get the message.

Incidentally double glazing multi-paned windows will not give you the same thermal efficiency as secondary glazing either as there will be thermal bridging through the numerous glazing beads and frame.

So in conclusion without the need for double glazing to be employed  a combination of the correct seals- that is compression seals for windows that close against the frame and wiper seals for parts that move against each other, sliding sashes come to mind. The closing of any gaps around the exterior of the frame. Curtains or blinds and secondary glazing will keep you warm and snug without compromising the aesthetics.

Balanced or Lifting Shutters

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The cords had broken on these shutters, and I could not locate the pockets to access the weights in order to re-cord them. I had to refer to a publication by George Ellis titled ‘Modern Practical Joinery’, printed in 1902, for the answer. As you can see, the pockets had been cleverly hidden behind the panel which I found surprising as I could just at a push get my arm into the cavity. Perhaps in those days arms were not so big, or this kind of work was undertaken by an apprentice with slender arms.

What I didn’t want to do was to take off the front panel to access these pockets; it’s been fixed in place since the 1850s. The windows are the original, fitted in 1796, but the balance shutters are a later addition. This was established by the presence of the original skirting board inside the shutter case. Also, the building was once owned by the Church and had a reliable record of works carried out over the last  two centuries.

Sometimes the pocket sits near the top of the frame, about 18” down from the pully wheels, which I now understand became the practice during the early part of the 20th Century.

Whilst doing this work it occurred to me what a fantastic way to eliminate drafts, light and noise. Those late Georgian / early Victorian designers really did think of everything, and the skill employed by the carpenters and joiners, with limited rudimentary  machinery, I can only admire and take my hat off to.

I am hoping that one day I will get an enquiry asking how can I eliminate drafts, light and noise with box sash windows fitted, as I would relish the opportunity to manufacture and fit a 21stcentury copy of such a practical solution to an age old problem.

There are modern day solutions that can be employed to reduce considerably the draft and noise problem associated with box sash windows, and these are covered in previous work and articles on this web site. I am happy to undertake such work but the elegance of balance or lifting shutters cannot be matched.

New for old: Replacing Window Frames

The wooden frames to this turn of the 20<sup>th</sup> century property were in a remarkable condition, the owner had records going back to 1930 showing a schedule of maintenance, the house had been in the family since it was built! however the openers to three frames had rotted and required replacement, they were very keen not to have plastic replacements which incidentally two builders whom had been approached had stated was the ‘only way to go with this’. Here you can see the manufacture and fitting of replacement timber openers, I copied the original mouldings in order for the end product to be an exact copy of the original.

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Porch in Southampton

This particular porch is in good condition apart from the corner post and cill. The rotten timber was cut out and a hard wood replacement offered up and glued in place, Merranti was used for the post and the cill, the original being an inferior pine, that however was not the cause of this rot, a leaking gutter above on the corner was to blame.


Draught proofing

Proofing Sash Windows
Sash windows can be draughty, particularly older examples. In fact the total amount of escape of heat around a box sash window is equivalent to having a hole about 4” square to the outside world. Fitting double glazing alone, if its possible (and usually its not), will not materially make any difference when it comes to draughts or saving heat escaping. Even if double glazing can be fitted, the units may blow and fill with condensation, thus any financial gain will be lost when you have to replace them. Most new plastic window guarantees do not usually include the double glazed units for that very reason.
The answer is to improve the existing sash windows by replacing the staff and parting beads with new timber beads that have a brush pile fitted into pre cut grooves. There are other benefits beside proofing against draughts: there will be the reduction of outside noise migrating into your home and the elimination of rattle. If you add thick curtains, which really do work, then you can be assured of a snug, warm home without desecrating the appearance of a period-windowed property.
So how do I draught and rattle proof those sash windows, with the added benefit of sound reduction? To begin with, I remove the two sashes and fit replacement cords. It’s good practice to do this at the same time rather than reuse old cords. Often they may look fine and certainly work alright, but UV light will have weakened the section of the cord that is exposed to light. Cords, particularly the unwaxed ones often fitted in older windows, are prone to this weakening. At the same time I check the putty. If this is cracked, or has parted from the glass, it needs to be raked out and replaced. Putty that has failed is the number one cause of rot in wooden windows.
Once these two items have been attended to, the next thing to do is to machine out a 2mm groove on the meeting rail (the bottom rail of the top sash and the top rail of the bottom sash), and also to machine out a 2mm groove on the bottom rail that sits directly onto the cill. Into this groove a flexible seal is inserted. At this point I assess the gap between the edge of the window and the box; if this is slack then further grooves are machined along the edge of the window – the stiles – and a brush seal inserted. Finally, parting beads with pre-machined brush seals are fitted, reversing them at the meeting rail so that the brush sits against the face of each window.  The staff beads with pre-machined brush seals are then fitted. The parting and staff beads are timber; plastic ones are available but they don’t quite look right.
Proofing Casement Windows.
The above mentioned issues with sash windows are common with casement windows as well. Modern (and by that I mean post 1970s) casements are often already fitted with an ‘aqua’ seal or at least the remnants of one. Often I see these windows with the groove machined to accept the seal but no seal. If it is the case that there is either no seal or a degraded one, then a replacement can be fitted without too much effort. If this is not the case, such as for pre 1970s casements, then a replacement window stop will need to be fitted, with the appropriate groove machined and the seal inserted. I can copy most mouldings found on window joinery so there should be no material difference between your old stops and replacement ones, although you will need to paint them. This may be important on period buildings, and insisted upon for listed buildings, or you may wish to simply keep the visual appearance the same.
At the same time as undertaking this work, I check the putty for defects and I also check the throat that should run around the whole casement. Often it is full of paint or missing. I have mentioned throating in another article on this website, but simply put its job is to prevent water sitting between the window and cill, which results in rot, and to prevent water being blown in during wet and windy weather. It’s simply a groove around 5mm wide and 3mm deep. The seal itself is available in white or brown and closes any gaps between 1 and 5mm.
Often I am asked to fit a replacement exterior door, usually the main entrance or back door, but sometimes full sets of French doors, because ‘this one is draughty’. The door itself is often perfectly adequate and in good condition. To reduce and possibly eliminate draughts, and therefore heat loss, one starts with the door frame. A brush seal is fitted to the frame which will close the gap between the door and the frame stops, not only reducing heat loss but also eliminating the daylight that you can often see along the edge of the door when it is closed, particularly on sunny days. A  brush seal along the bottom of the door has the same effect. If the door stops are nailed or screwed onto the frame, these can be removed and replacement stops fitted, with a ‘aqua’ seal inserted into a machined-out groove, much the same as for casement windows as mentioned earlier. If the stops are part of the frame, and this is usually the case, then a groove can be machined around the edges of the door instead and a brush pile inserted – the same method that is employed in weather sealing box sash windows. This brush pile sits proud by about 1.5mm to 3mm. A combination of exterior draught excluder, brush pile or ‘aqua’, and bottom brush will have a massive impact on heat loss and reduce considerably noise from outside. A final weapon in the tool box is a letter plate draught excluder fitted over the letter plate aperture on the inside of the door.
So all in all, if you are fortunate enough to live in a property which has retained its original ‘pre-plastic’ windows and doors, it is not inevitable that you have to suffer draughts and high heating bills.

Renovations of a double bow window

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This particularly fine example of a double bow window manufactured and installed in the early 1950s was made by Crittal, who have been trading since 1849 originally in Braintree Essex. The steel windows are almost as good as the day they were made a testament to their quality, the cills were also surprisingly in a reasonable condition although each meeting joint had to be scarfed. The customer who was very pleased with the results was originally quoted over £25,000 for replacement! I came in at a fraction of that price,  There was absolutely no good reason to have these replaced, all they required was a’ birthday’ which will see them through for another 60yrs

Plastic out – wooden in

I was asked to replace a french bay, the original timber bay was replaced 17yrs ago with this plastic substitute.
i was given a photograph taken before the old bay was replaced.
Using only this as a guide, i was able to reproduce a copy of the original french bay, the only difference between the old and the new being a different door.
Fourtunately the customer had the foresight to save the old stained glass windows after rumaging around in a very dusty loft, they were found along with the photo shown.
This though did present a bit of a challange, normally the glass is the last thing to size when making something like this, having the original glass meant that not only must the whole bay fit the brickwork, but it had to fit the glass as well  
I was keen to reproduce something that was as close to the original as possible, so i researched joinery books from the 1930’s to establish the mouldings that would have been used .
So after about 120hours the end result. I have now been asked to replace to original specification, all the exterior windows and doors, bringing this 1930’s house back to its former glory.
The customer who has lived in the property many years said that when she dies ‘ she wishes to pass the house on as it should be’  

Double glazed units fitted into existing windows:

This is something I am asked about frequently. It depends on the style of window you have and the thickness of the openers or sashes. Unless I am taking out double glazed units and replacing them, the rebates will need to be altered to accommodate the extra thicknesses of the double glazed units. The thinnest units available are 11mm, which have 3mm glass, a 5 mm spacer, and 3mm glass. These are known as a 3-5-3.  The next size up, which incidentally is cheaper, is a 4-6-4: 4mm glass, a 6mm spacer, and 4mm glass, giving a total thickness of 14mm.


This extra thickness needs to be accommodated in the rebate which has been manufactured to accommodate 4mm glass or on older box sash windows 3mm glass. This alteration to the rebate can come with problems, to begin with it may weaken the actual frame that the glass sits in i.e.: the opener or sash. Timber beading as opposed to putty has to be used to keep them secure, extra width may be required to cover up the edging around the double glazed unit. This can throw your eye towards this and can take away the originality of your period windows, also if you have original glass it may well be  drawn glass as opposed to float which has a regular flat appearance this again can throw your eye towards this change of glass, and to be frank it doesn’t look right. Another consideration is the extra weight particularly with box sash windows this has to be counteracted with new sash weights which can be costly particularly if the pocket that the weights go into are too small to take the extra length of a bigger steel/iron weight and a lead weight has to be used instead.

You may have gathered at this point that I am no fan of double glazed units, single pieces of glass have an approximate life span of 800 years, double glazed units 15 perhaps 20 years before they ‘blow’ and condensation then becomes a problem in the space between the glass.  Replacement really does mean replacement every 15/20 yrs! Indeed with modern plastic windows the guarantee more often than not does not cover the glass units, only the plastic and window furniture.

So what’s the solution? There are ways to overcome the inherent issues that you may be experiencing with draughts and maybe sound from outside, the first one is to perhaps consider investing in some thick curtains, they really do make a difference, or perhaps the fitting of acoustic and thermal seals, rubber strips that are fitted after a suitable groove has been machined on the edges of your openers or if you have box sash windows, brush seals fitted to parting and sash beads. Another viable option is secondary glazing, either fixed to the inside of the window frame, or  sliding or the manufacture and fitting of a second window within the revel that opens inwards this option is common in many parts of Europe and was also employed in this country in the late 1800s in the centre of towns and cities.




An annual visual check and action on potential weak spots, coupled with a 5-7 year cycle of re-painting, will be sufficient to protect your timber windows for many years. The oldest windows I worked on were installed in the 1700s. They were ‘tired’ but because they had been included in a maintenance programme over the centuries (the windows were part of a church estate), they were in remarkably good condition.

Moisture readings:

As a matter of course I measure the moisture content of your windows, starting at the cill and moving up every 6” until I get a reading of between 12 and 18 percent. This will give me the information I need to asses the extent of potential wet rot areas. On average no more than 10% of any given window will be rotten, including the cill.  Repair rather than replacement will be economically viable in all but the most exceptional cases of damaged of frames and openers.  Of all the windows in a year that I assess, I see perhaps five percent that are beyond economical repair. In these few cases, it is cheaper for me to manufacture and fit like-for-like wooden replacements.

What is wet rot?

Essentially, it’s a fungal attack on timber that has high moisture content for an extended period of time. There are two main types: white and brown, with several less common types also in existence.  You can easily identify both white wet rot and brown wet rot. The former has the appearance of fine threads and often a soft white tissue structure. This type is usually found between openers and cills or transoms. Brown rot appears as cracked cube structures, often brown and brittle, found on exposed timber and joints. Of the two, white rot is probably more destructive as sometimes the fine hairs can travel onto masonry.

Treatment is the same for both: cut it out and replace the affected area with new timber. If the spores from white rot have penetrated the brick this will need to be treated with an appropriate chemical solution.


Window glossary: Here you can see the common terms used when describing windows.

Rot in openers and sliding sashes:

The number one cause of rot, it cracks over time, usually starting in the corners, water gets in, and the damage starts.  Water sits in the rebate where it has no means of drying out sufficiently, until next winter arrives, bringing more rain and, for good measure, a frost, which freezes the water between the glass and putty. This then expands, letting in more water, and the cycle repeats.  These events will set in motion wet rot behind the putty in the rebate. If the damage is in the corner of the window, the joints between the bottom rail and stiles, mullions, and glazing bars start to suffer as well. It would be wise to check the putty on your windows once a year; it only takes five minutes, and if it is showing signs of degrading then get it raked out and a fresh bead put back in. You can tell if new putty is needed by seeing if there are any cracks in the putty or if it has come away from the glass, in which case you often see moss or dirt between the glass and putty.

Other causes of wet rot in openers can be as described above for window frames: poor quality paints, problems regarding the throat, shrubs, and leaking gutters.

Below highlighted in red are the most common areas vulnerable to wet rot.


Rot in window frames:

There are very few instances where a window frame has become damaged by rot any significant distance above the cill.  Such rare instances have four main causes: when water gets into the drip bar or the transom; when a closed opener sits tight on the transom leading to capillary action; when the opener loses the throating, usually the result of swelling, so someone shaves off the bottom rail so that the opener fits again and doesn’t put in a new throat; or finally when the throat has become filled with layers of paint over the years. There is a reason why the throating should be present all around the opener: it is to stop capillary action taking place.

image for new window site image shows just how bad a double glazed unit can leak note the level of the water this particular unit was 20yrs old

The most common area where you will see rot is in the corners of the cill and in the first 6” on the frame jamb.  It can be caused by the above mentioned faults, or by the pooling of water in the corners coupled with a poor paint surface.  If the paint cracks at this crucial joint and water seeps in, the water has no where to go and no means of drying out, perfect conditions to allow wet rot to take hold.

Other causes of wet rot can be: poor quality paints allowing moisture penetration; painting timber with a high moisture content; timber of inferior quality (usually not applicable to pre 1970s frames); shrubs growing too close or against the timber; and gutters that leak.

Replacement of rotten cills to a former Victorian school in Southampton

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Replacement of rotten cills to a former Victorian school, the grooves in the brickwork were made by pupils in the 1800s that used the bricks as a sharpening stone for their pencils, a marine primer was used to protect the new cills until a painter can finish in the desired gloss.

Secondary glazing

Secondary glazing manufactured and fitted to a timber bay window. This format of secondary glazing is common in Europe. Essentially, a second window is fitted into the reveal. The secondary windows open inwards so the original bay window remains intact with its windows opening outwards. This type of secondary glazing is less conspicuous than aluminium sliding secondary glazing and it works well in keeping out draughts as well as traffic noise, which is particularly useful if you live on a main road.

secondary window repairs Southampton2 secondary window repairs Southampton secondary window repairs Southampton4 secondary window repairs Southampton3

Repairing a rotted window

These images show the process of repairing a rotted corner in an otherwise sound hardwood window frame. This rot occurred almost certainly due to the failure of the rubber draught seal that is fitted to this type of window. Over time, the rubbers can become compressed and tired, which weakens the seal, allowing water to ingress and resulting in the rot. You can replace this seal relatively cheaply. It can be purchased in rolls of 50m and you simply cut it to length, then fit it after removing the old seal. Be sure though to get the correct profile (the shape of the cross section). Most suppliers will send a sample on request so that you can make sure. Catch this problem before it starts and you can save a lot of money and effort in having to replace or repair window frames and cills.

rotten window

old windowwindow in southampton