Maintaining Timber Windows
A well-maintained timber window is a significant element of the historical fabric of a building. It is a representation of the materials and technologies, craftsmanship and architectural taste of the time from which it originates.
If possible, repairs should be done in-situ. Repairing the most deteriorated areas of decay can be accomplished using proprietary resin-based systems.
Durability
The windows made of wood in many historical structures were designed to last for hundreds of years. However, they do need to be maintained to ensure they look great and working correctly. Maintenance tasks include repairs to sash cords as well as tightening the pulleys on sash, and painting. The demand for upgrading timber windows in order to improve efficiency in energy use is also growing. This may mean replacing old glass units, repairing the window rebates that are in place, or installing new cills that allow the air to seal better.
A key problem with traditional windows is damage caused by the corrosion of the paintwork. This is especially true in the case of sash windows, as the gaps between sashes can often be very large. In these cases, water can penetrate paint film and cause rotting of the putty or wood beneath. The rotting may be further aggravated by weather conditions that are not ideal. To prevent this from happening, windows should be regularly painted with an exterior wood paint.
The areas that are damaged should be repaired using a resin-based product. This will ensure that the highest possible amount of the original fabric is preserved. It is crucial to reduce the number of holes that are created in the frame to allow cable access, since they can let in moisture and cause decay.
The structural movement of the wall could also cause distortions in the frame and the sash. This could result in the sash not fitting properly jamming, sticking or sagging in the opening, and even broken glass. This can be corrected often by putting in new sash frames made of slow-growing deal (pine) or oak. The cill should be constructed of a strong hardwood like oak, to avoid differential movement between new and old work.
There are now several companies that produce Boston pattern wooden sash to fit most existing openings. The sash is available in various sizes and finishes to fit the needs of modern homeowners. The new sash, coupled with quadruple draft strips and a more efficient thermal insulation, could significantly improve the energy-efficiency of a home.
Aesthetics
Many old timber frames have a high aesthetic appeal, as they reflect, in some form, the materials, technology, and architectural aesthetics of the time they were made. They could also have a significant historic value in their own right. This is especially true for early windows that were not glazed in timber-framed buildings, where the great majority were merely a series of openings in the frame, which were divided horizontally into mullions and iron or wood bars to deter intrusions.
Traditional timber window joinery can be a highly decorative feature of a building and it is important to keep it looking good. It is crucial that any decay resulting from the penetration of moisture should be stopped as soon as it is discovered. It is best to do this with thorough painting, especially if there is damage or degradation. It is advisable to use paints specifically designed to be used part of a system (primer as well as undercoat, finish and primer) and to follow the manufacturer's recommendations in terms of preparation and the number of coats needed at each stage.
Wet rot is a typical problem in older timber windows. The best method to stop it from developing is to remove any damaged or rotten parts as soon as possible to stop the spread of the fungus that causes it. Replace rotting wood with slow-growing deal (pine) and, when possible, the exact type of timber as the one being removed to prevent differential movement.
Glass became cheaper and more abundant during the late medieval period and into the 17th century. This led to glazed openings on timber-framed houses became more complicated with moulded mullions and traceries, made of wood and deep cills projecting into the air. Increasingly, the glazing was placed within frames with rebates and then pinned with 'glazing sprigs', rather than being inserted into lead cames. This method of glazing not only makes the windows less likely to leak and also allows more clear glass sheets to be used than would have been possible without the use of leaded lights.
Energy efficiency
Traditional timber windows provide excellent energy efficiency due to their thickness, multi-layer construction and very careful attention to detailing. They also feature large glass areas as well as deep projecting cills that reduce air infiltration. The windows can be modified to improve their energy efficiency by draught-proofing and secondary glazing. However it is crucial to keep in mind that these measures must be considered in relation to the overall integrity and appearance of the window in its original form.
So, retaining existing historic windows that require repair rather than replacing them is sensible particularly when thermal enhancements can be achieved economically through simple repairs and improvements. Historic windows often have an historic value that demonstrates a range of technological advancement and changes in architectural style. Most people think that these windows will need to be replaced in the near future. However, they can still provide service for 150, 200, or even 250 years with proper maintenance.
It is essential to understand that the decay problems caused by traditional timber windows can be avoided through regular maintenance and swift repairs. In addition, it is essential to recognize damp penetration issues and fix them promptly to avoid major damage. Early paint deterioration is a major issue, as it allows moisture to penetrate the wood and cause wet rot. It is not uncommon for this type of damage to go undetected until the paintwork starts to crack or turn wavier. However, it could cause structural damage and lead to further decay.
A good paint will block moisture penetration. To prevent mould and condensation it is essential to keep the paintwork as clean as you can. Modern synthetic paints pose a problem since they are usually water-resistant and may cause mildew growth within the window frame.
Most older windows were made from sapwood-rich timber. The timbers will deteriorate quickly when exposed to moist weather, however they can be protected by an extensive preservative treatment prior to when they are put to use. It is also important to ensure that the type of timber used is well-suited to the location and climate conditions, as these elements affect the durability of the joinery. Local window manufacturers provide various types of sash made from timber that can be customized to fit historic openings. They can be constructed according to the standard Boston pattern dimensions or to double glazing repair cambridge specific sizes that fit with the architectural style of historic buildings.
Maintenance
The life span of windows made from timber can be extended by regular inspection carefully redecoration, and prompt repair. The main cause of decay is the infiltration of moisture through deteriorated paint and putty. This can be prevented by using a good wood preservative and thoroughly painting the wood.
It is crucial that repairs to the old sash and casement windows are done correctly, and carried out without causing any disturbance. Many of the traditional designs for timber windows can be repaired without removing the frame, and this approach should be taken whenever feasible. Remove any peeling or loose paint and lightly sand the area to improve the 'key" of the surface. This will allow the new coating to adhere better. It is important to avoid removing old paint layers, which may have historical value.
If a portion of wood has rotted the best way to deal with it is to remove it and replace it with timber inserts designed to match the existing profiles. The inserted timber should also be treated with a wood preservative, and the joint between the masonry sub-cill and the timber cill should be sealed.
Replacement of traditional windows using PVC-u is an appealing option, particularly when the installer provides a "one-stop shop" installation that takes care of removal and replacement in one day. It is vital that the installer of replacement windows has a complete knowledge of the construction and history of traditional timber frames. This will enable them to make appropriate recommendations for energy efficiency improvements and other technological upgrades that won't harm the historical character of a building. Those providing replacement windows should be registered with a Competent Persons Scheme like FENSA. This will ensure that the replacement windows are approved as a suitable solution under Building Regulations. It is, of course, possible for an experienced and skilled carpenter to install PVC-u windows that are sympathetic to the character of the building originally. This is especially true where the windows are located in listed buildings or conservation areas.