Maintaining Timber Windows
A well-maintained wooden window is an essential element of a building that is historic. It is a representation of the different materials and technologies, craftsmanship and architectural taste of the time period that it was built in.
When possible, repairs should be made on-site. Repairing the most severe areas of decay is possible using proprietary resin-based systems.
Durability
The windows made of wood in many historic buildings were made to last for hundreds of years. They do require maintenance to keep them looking great. Maintenance tasks include repairs to sash cords and retightening pulleys for sash and painting. The need to upgrade windows made of timber to improve energy efficiency is also growing. This could mean replacing old glass units, fixing existing window rebates, or installing new cills that allow for better air sealing.
The corrosion of paintwork is a major problem with traditional windows. This is especially important in the case of sash windows because the gaps between sashes can be very large. In these cases water can get into paint film and cause rotting to the wood or putty underneath. The rotting can be exacerbated due to weather conditions that are poor. 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 remains. It is important to minimize the number of holes that are drilled in the frame to allow cable access, because they could let in moisture and cause decay.
Another issue with older windows is structural movement in the wall that can lead to deformation of the frame and the sash. This could result in sash no longer fitting correctly or sticking or jamming into the opening and broken glazing. This can be corrected often by fitting new sash frames constructed of slow-grown deal (pine), or oak. The cill must be constructed from a sturdy hardwood such as oak to avoid any movement between the existing and new work.
There are now several companies that make Boston pattern wooden sash that fit most existing openings. They are available in a range of sizes and finishes that meet the needs of the modern homeowner. Together with quadruple draught strips and better thermal insulation these new sash options can make a substantial difference to the energy efficiency of a house.
Aesthetics
Many old timber frames possess a dazzling aesthetic appeal, as they show, in some form, the quality of the wood technology, design, and taste from the time period they were made. They could also have significant historical value in their in their own right. This is especially true of early unglazed windows in timber-framed buildings, in which the majority were series of openings within structural frames subdivided horizontally by mullions and vertical wood or iron bars in order to keep out intrusions.
It is essential to preserve the appearance of traditional wooden window joinery. It is crucial that any decay caused by moisture penetration should be immediately stopped once it is discovered. This can be done by painting thoroughly, especially in areas where there has already been damage or deterioration. It is recommended to choose paints that are intended to be used in a set (primer undercoat and finish) and to follow the manufacturer's guidelines for preparation and number of coats at each stage.
Wet rot is a typical issue in old timber windows. The best method to stop it from becoming a problem is to take out any damaged or rotten parts as soon as you can to stop the spread of the fungus responsible for it. Replace rotting wood with slow-growing deal (pine) and, if possible, the same kind of timber as the one being removed, to prevent differential movement.
Glass became less expensive and more abundant during the late medieval period and into the 17th century. In the process, the glazed openings in timber-framed homes became more complex with moulded mullions and traceries, made of wood and cills that protruded deep. In the past, more often, the glass was laid within rebated frames and secured with 'glazing sprigs' rather than being inserted into lead cames. This method of glazing is not just less prone to leaking but it can allow for larger clearer, more transparent sheets of glass to be used in windows than would have been possible without the need for lead lights.
Energy efficiency
Traditional timber windows have excellent energy efficiency due to their thickness, multi-layer construction and very meticulous attention to detail. They also have large glass areas as well as deep projecting cills that reduce air infiltration. The windows can be modified to improve their energy efficiency with draught-proofing and secondary glazing. It is essential to remember that these measures need to be considered when it comes to the overall integrity and look of the original windows.
It makes sense to repair or upgrade existing historic windows rather than replace them, especially when the improvements in energy efficiency can be made by simple repairs. Older windows typically have historical significance that demonstrates a range of technological advancement and changes in architectural style. The pressures to replace such windows are usually based on the assumption that windows of the past will require replacement in the near future, however the majority of them are in a position to last for 150, 200 and even 250 years, if properly maintained.
It is important to recognise that the decay problems caused by traditional windows made of timber can be avoided by regular maintenance and timely repairs. In addition it is crucial to spot damp penetration issues and to remedy them quickly to avoid major damage. The early deterioration of paint can be a problem because it allows moisture to get into the wood, leading to wet rot. This damage is often not noticed until the paintwork becomes damaged or wavy but it can cause severe structural damage and can lead to further decay.
A good quality paint will prevent this moisture penetration. To prevent mould and condensation, it is important to keep the paintwork as clean as you can. Modern synthetic paints pose a problem because they are water-resistant and may cause mildew to grow in the window frame.
The majority of windows from the past were constructed of sapwood-rich timber. These timbers deteriorate quickly if exposed to rain, but they can be preserved with a thorough preservation treatment before use. It is also important to ensure that the kind of timber used is well-suited to the climate and site conditions, since these factors affect the durability of the joinery. Local window manufacturers have an array of timber sash which can be made to fit the historic openings. They can be made according to the standard Boston pattern dimensions, or to custom sizes that fit with the architectural style of historic buildings.
Maintenance
The life of timber windows can be extended through regular inspections, careful redecoration and timely repair. The primary cause of decay is the infiltration of moisture through deteriorated putty and paint. This can be prevented by using a good wood preservative and painting the wood thoroughly.
It is essential that repairs to the old sash and casement windows are properly executed and done with minimal disruption. Many of the traditional designs for timber windows are repairable without removing the frame, and this approach should be taken whenever feasible. Paint that is peeling or loose must be removed with care and sanded lightly to increase the "key" of the surface, allowing for an easier adhesion of the new coating. It is important to avoid stripping paint layers that might have historical significance, and where these are present, it is recommended that a study of the paint be conducted.
Where a section of timber has begun to decay, the best way to proceed is to take out the rotten material and replace it with spliced-in inserts that are shaped to match existing profiles. The wood that is being inserted should be treated with a wood preservative and the connection between the cill for timber and the sub-cill of the masonry should be sealed.
Replacement of windows made of traditional PVC-u is a tempting option, especially when the installer provides an "all-in-one" installation that takes care of removal and replacement in one day. It is important that the installers of replacement windows have a deep understanding of the history and design of traditional timber frames. This will allow them to make the right suggestions for improvements to energy efficiency and other technological upgrades that double glazing in cambridge won't harm the character of a historic building. Those providing replacement windows should be registered with a Competent Persons Scheme such as FENSA. This will ensure that the replacements are approved by the Building Regulations as a suitable option. It is certainly possible for a skilled and experienced carpenter to install PVC-u windows that match the style of the original building. This is particularly true when the windows are located within listed buildings or conservation areas.